Elecsys Syphilis
Device Facts
| Record ID | K160910 |
|---|---|
| Device Name | Elecsys Syphilis |
| Applicant | Roche Diagnostics |
| Product Code | LIP · Microbiology |
| Decision Date | Jul 28, 2016 |
| Decision | SESE |
| Submission Type | Traditional |
| Regulation | 21 CFR 866.3830 |
| Device Class | Class 2 |
Intended Use
Immunoassay for the in vitro qualitative determination of total antibodies (IgG and IgM) to Treponema pallidum in human serum and plasma. The test is intended as an aid in the diagnosis of syphilis infection in conjunction with clinical signs and symptoms. The Elecsys Syphilis immunoassay is not intended for use in screening blood or tissue donors. The effectiveness of this assay in testing blood or tissue donors has not been established. The electrochemiluminescence immunoassay "ECLIA" is intended for use on the cobas e 411 analyzer. PreciControl Syphilis is intended for the quality control of the Elecsys Syphilis immunoassay on the cobas e 411 analyzer.
Device Story
Fully automated, qualitative electrochemiluminescence immunoassay (ECLIA) for detection of total anti-T. pallidum antibodies (IgG/IgM) in human serum/plasma. Uses double antigen sandwich format: recombinant T. pallidum antigens labeled with biotin or ruthenium complex bind to patient antibodies; complex binds to streptavidin-coated microparticles immobilized magnetically on electrode. Voltage application induces chemiluminescent emission measured by photomultiplier. Performed on cobas e 411 analyzer by laboratory personnel. Output is cutoff index (COI) value; COI ≥ 1.0 is reactive, < 1.0 is non-reactive. Results aid clinical diagnosis of syphilis when interpreted with clinical signs, symptoms, and other serologic tests. Benefits include automated, high-throughput screening for syphilis infection.
Clinical Evidence
Clinical study of 2,660 specimens (2,282 prospective, 169 retrospective, 209 healthy). Performance evaluated against a composite comparator (treponemal chemiluminescent immunoassay, RPR, and TP-PA). Prospective cohort: 100% PPA (228/228; 95% CI: 98.4-100.0%) and 99.2% NPA (2038/2054; 95% CI: 98.7-99.6%). Retrospective cohort: 98.7% PPA (155/157; 95% CI: 95.5-99.9%) and 100% NPA (12/12). No invalid results reported.
Technological Characteristics
Double antigen sandwich electrochemiluminescence immunoassay (ECLIA). Uses biotinylated and ruthenium-labeled recombinant T. pallidum antigens (TpN15, TpN17, TpN47). Solid phase: streptavidin-coated microparticles. Detection: chemiluminescence via photomultiplier. Instrument: cobas e 411 analyzer. Sample types: serum, K2/K3 EDTA, Li-Heparin, Na Citrate, CPDA plasma. Qualitative output based on 1.0 COI cut-off.
Indications for Use
Indicated for the qualitative detection of total antibodies (IgG and IgM) to Treponema pallidum in human serum and plasma as an aid in the diagnosis of syphilis infection. Not for use in screening blood or tissue donors.
Regulatory Classification
Identification
Treponema pallidum treponemal test reagents are devices that consist of the antigens, antisera and all control reagents (standardized reagents with which test results are compared) which are derived from treponemal sources and that are used in the fluorescent treponemal antibody absorption test (FTA-ABS), the Treponema pallidum immobilization test (T.P.I.), and other treponemal tests used to identify antibodies to Treponema pallidum directly from infecting treponemal organisms in serum. The identification aids in the diagnosis of syphilis caused by bacteria belonging to the genus Treponema and provides epidemiological information on syphilis.
Predicate Devices
- Immulite 2000 Syphilis Screen test system (K091361)
Related Devices
- K211302 — Elecsys Syphilis · Roche Diagnostics · Jul 20, 2021
- K241427 — Access Syphilis · Beckman Coulter, Inc. · Sep 6, 2024
Submission Summary (Full Text)
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# 510(k) SUBSTANTIAL EQUIVALENCE DETERMINATION DECISION SUMMARY
A. 510(k) Number:
K160910
B. Purpose for Submission:
To establish substantial equivalence to a predicate device and to obtain market clearance for a new assay designed to detect antibodies to *T. pallidum* in human serum and plasma.
C. Measurand:
Antibodies to *T. pallidum* (IgM and IgG)
D. Type of Test:
A qualitative double antigen sandwich electrochemiluminescence immunoassay for use on the cobas e 411 analyzer.
E. Applicant:
Roche Diagnostics
F. Proprietary and Established Names:
Elecsys Syphilis
G. Regulatory Information:
1. Regulation section:
866.3830
*Treponema pallidum* treponemal test reagents
2. Classification:
Class II
3. Product code:
LIP, enzyme linked immunoabsorption assay, *Treponema pallidum*
4. Panel:
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Microbiology (83)
## H. Intended Use:
1. Intended use(s):
**Assay:**
Immunoassay for the *in vitro* qualitative detection of total antibodies (IgG and IgM) to *Treponema pallidum* in human serum and plasma. The test is intended as an aid in the diagnosis of syphilis infection in conjunction with clinical signs and symptoms.
The Elecsys Syphilis immunoassay is not intended for use in screening blood or tissue donors. The effectiveness of this assay in testing blood or tissue donors has not been established.
The electrochemiluminescence immunoassay “ECLIA” is intended for use on cobas e 411 analyzer.
**Control:**
PreciControl Syphilis is intended for the quality control of the Elecsys Syphilis immunoassay on cobas e 411 analyzer.
2. Indication(s) for use:
Same as Intended Use.
3. Special conditions for use statement(s):
For Prescription Use
4. Special instrument requirements:
cobas e 411 analyzer
## I. Device Description:
**Assay**
The Elecsys Syphilis immunoassay is a fully automated, qualitative assay that uses a double antigen sandwich format for the detection of IgM and IgG antibodies to *T. pallidum*. Recombinant *T. pallidum* antigens labeled with either biotin or a ruthenium complex bind to *T. pallidum*-specific IgG or IgM to form a double antigen sandwich complex. The sandwich complex binds to streptavidin-coated microparticles which can be immobilized magnetically to the surface of an electrode. Unbound substances are removed during a wash step using ProCell. A chemiluminescent substrate is then added to the reaction tube. Application of a
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voltage to the electrode induces a chemiluminescent emission which is measured by a photomultiplier.
The presence or absence of anti-TP antibodies in the specimen is determined by comparing the chemiluminescent signal in the reaction to the cutoff index (COI) determined from an active calibration. The strength of the signal generated is proportional to the amount of bound enzyme and thus the amount of anti- $T$ . pallidum antibodies present in the specimen. If the chemiluminescent signal in the reaction is greater than or equal to the cutoff signal, the specimen is considered reactive for anti-TP antibodies. If the chemiluminescent signal is below the cutoff signal, the specimen is considered nonreactive for the anti-TP antibodies.
The results are printed out as follows:
COI $\geq 1.00$ Reactive
COI $< 1.00$ Nonreactive
## Interpretation of results:
Reactive Reactive for treponemal antibodies
Nonreactive Nonreactive for treponemal antibodies
Test results are intended to aid in diagnosis only. As with all serological tests for syphilis, results should always be interpreted in conjunction with additional treponemal or non-treponemal serologic test results (as appropriate), the patient's clinical symptoms, medical history, and other clinical and/or laboratory findings to produce a diagnosis of syphilis by disease stage.
All initially reactive samples should be retested in duplicate with the Elecsys Syphilis assay. If cutoff index values $< 1.00$ are found in both cases, the samples are considered negative for anti-Treponema pallidum antibodies.
Initially reactive samples with cutoff index values of $\geq 1.00$ in either of the retests are considered repeatedly reactive. Repeatedly reactive samples must be confirmed according to recommended confirmatory algorithms.
The PreciControl Syphilis 1 and 2 controls and Syphilis Cal1 and Cal2 calibrators are for use with the Elecsys Syphilis Assay.
## Syphilis Cal1 and Cal2 Calibrators
Provided with the assay; intended for the calibration of the Elecsys Syphilis immunoassay. The calibrators are provided as two $1.0\mathrm{mL}$ bottles of lyophilized human serum each. Cal1 contains human serum which is non-reactive for anti-TP antibodies. Cal2 contains human serum which is reactive for anti-TP antibodies.
## Elecsys Syphilis Assay Controls
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The PreciControl Syphilis 1 and 2 controls are intended for the monitoring of accuracy for the Elecsys Syphilis assay and are sold as an accessory. The controls consist of two bottles of human serum positive or negative for anti-Treponema pallidum antibodies plus a preservative. Target values for the cutoff index are available electronically or provided in the control reagent kit.
## J. Substantial Equivalence Information:
1. Predicate device name(s):
Immulite 2000 Syphilis Screen Test
2. Predicate 510(k) number(s):
K091361
3. Comparison with predicate:
| Characteristics | Elecsys Syphilis | Immulite 2000 Syphilis Screen Test System (K091361) |
| --- | --- | --- |
| Similarities | | |
| Intended Use | Immunoassay for the in vitro qualitative detection of total antibodies (IgG and IgM) to Treponema pallidum in human serum and plasma. The test is intended as an aid in the diagnosis of syphilis infection in conjunction with clinical signs and symptoms.
The Elecsys Syphilis immunoassay is not intended for use in screening blood or tissue donors. The effectiveness of this assay in testing blood or tissue donors has not been established.
The electrochemiluminescence immunoassay “ECLIA” is intended for use on cobas e 411 analyzer. | The IMMULITE 2000 Syphilis Screen test is a treponemal testing procedure for the qualitative detection of antibodies to Treponema pallidum in human serum or heparinized plasma on the IMMULITE 2000 analyzer as an aid I the diagnosis of syphilis.
The IMMULITE 2000 Syphilis Screen test is not intended for use in screening blood or plasma donors. |
| Analytes | Antibodies to Treponema pallidum | Same |
| Specimen Types | Serum and plasma | Same |
| Controls | 2 (Negative and Positive) | Same |
| Differences | | |
| Cut-off Index | <1.00 Non-reactive | <0.9 Non-reactive |
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| | ≥1.00 Reactive | ≥0.9 to <1.1 Indeterminate
≥1.1 Reactive |
| --- | --- | --- |
| Instrument | Cobas e 411 | Immulite 2000 System |
| Antigens used | Recombinant antigens TpN17, TpN15, and TpN47 | Recombinant antigen Tp17 |
| Sample types | Serum, K_{2} EDTA, K_{3} EDTA, CPDA, NaCitrate and Li Heparin | Serum, heparinized plasma |
| Assay methodology | Double antigen sandwich, electrochemiluminescence immunoassay | Enzyme labeled, single step chemiluminescent immunoassay |
## K. Standard/Guidance Document Referenced (if applicable):
Not applicable.
## L. Test Principle:
Electrochemiluminescence Immunoassay
## M. Performance Characteristics (if/when applicable):
### 1. Analytical performance:
#### a. Precision/Reproducibility:
**Internal Precision**
The precision of the Elecsys Syphilis assay was evaluated in an internal study using six human serum samples (spiked), the PreciControl 1 and PreciControl 2 controls, and one lot of reagents. Two replicates of each serum sample and control were tested two times per day for 21 days. Samples were run in randomized order on the analyzer. Human serum samples were prepared to create a panel of two negative samples (COI < 1.0), two low positive samples (COI approximately = 1.0), and two positive samples (COI > 1.0). The mean COI value, within-run Standard Deviation (SD) and percent coefficient of variation (%CV) as well as between-run SD and %CV were calculated for each group of samples and a summary of the results is shown below.
| | | | Repeatability | | Between Run | |
| --- | --- | --- | --- | --- | --- | --- |
| Sample | N | Mean COI | SD COI | %CV | SD COI | %CV |
| HS^{1}, negative 1 | 84 | 0.103 | 0.002 | 1.6 | 0.003 | 3.2 |
| HS, negative 2 | 84 | 0.821 | 0.0174 | 2.1 | 0.019 | 2.3 |
| HS, low positive 1 | 84 | 1.01 | 0.028 | 2.8 | 0.033 | 3.2 |
| HS, low positive 2 | 84 | 1.12 | 0.018 | 1.6 | 0.022 | 1.9 |
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| | | | Repeatability | | Between Run | |
| --- | --- | --- | --- | --- | --- | --- |
| Sample | N | Mean COI | SD COI | %CV | SD COI | %CV |
| HS, positive 3 | 84 | 9.99 | 0.171 | 1.7 | 0.262 | 2.6 |
| HS, positive 4 | 84 | 50.2 | 0.986 | 2.0 | 1.24 | 2.5 |
| PreciControl Syphilis1 | 84 | 0.106 | 0.003 | 2.4 | 0.004 | 4.1 |
| PreciControl Syphilis2 | 84 | 4.95 | 0.101 | 2.1 | 0.161 | 3.2 |
1) $\mathrm{HS} =$ human serum
# Multi-site Reproducibility
A reproducibility study was conducted following CLSI EP5-A2 at three sites incorporating a seven member panel consisting of five serum pools: high negative (COI $< 1.0$ ; HSP 08 and HSP09), low positive (COI close to 1.0; HSP 06 and HSP 07) and moderate positive $(\mathrm{COI} > 1.0$ ; HSP 10). The five serum pools and two controls were assayed for five days, two runs per day, and three replicates per sample. Data from all three sites were combined to examine the standard deviation and percent coefficient of variance for repeatability within-run, between run, between-day, between site, and overall reproducibility. Data are summarized in the tables below.
| | | Mean | Within Run Repeatability | | | Between Run | |
| --- | --- | --- | --- | --- | --- | --- | --- |
| Sample | N | COI1 | SD2 | 95% CI | %CV | SD | %CV |
| HSP306 | 90 | 1.02 | 0.01 | (0.01, 0.01) | 1.16 | 0.02 | 2.28 |
| HSP 07 | 90 | 1.13 | 0.02 | (0.02, 0.03) | 1.90 | 0.03 | 2.57 |
| HSP 08 | 90 | 0.94 | 0.01 | (0.01, 0.02) | 1.58 | 0.02 | 2.55 |
| HSP 09 | 90 | 0.85 | 0.02 | (0.01, 0.02) | 1.88 | 0.02 | 2.49 |
| HSP 10 | 90 | 3.24 | 0.09 | (0.08, 0.11) | 2.78 | 0.08 | 2.61 |
| SYPH PC14 | 90 | 0.12 | 0.00 | (0.00, 0.00) | 2.41 | 0.00 | 2.39 |
| SYPH PC2 | 90 | 4.76 | 0.08 | (0.07, 0.10) | 1.65 | 0.14 | 2.89 |
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| | | Mean | Between Day | | Between Site | | Overall Reproducibility | | |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Sample | N | COI | SD | %CV | SD | %CV | SD | 95% CI | %CV |
| HSP 06 | 90 | 1.02 | 0.00 | 0.00 | 0.01 | 1.29 | 0.03 | (0.02, 0.04) | 2.86 |
| HSP 07 | 90 | 1.13 | 0.00 | 0.00 | 0.01 | 0.79 | 0.04 | (0.03, 0.05) | 3.29 |
| HSP 08 | 90 | 0.94 | 0.00 | 0.00 | 0.01 | 0.75 | 0.03 | (0.02, 0.04) | 3.09 |
| HSP 09 | 90 | 0.85 | 0.00 | 0.00 | 0.01 | 1.23 | 0.03 | (0.02, 0.04) | 3.36 |
| HSP 10 | 90 | 3.24 | 0.00 | 0.00 | 0.00 | 0.00 | 0.12 | (0.11, 0.15) | 3.82 |
| SYPH PC1 | 90 | 0.12 | 0.00 | 1.15 | 0.01 | 4.47 | 0.01 | (0.00, 0.02) | 5.73 |
| SYPH PC2 | 90 | 4.76 | 0.00 | 0.00 | 0.03 | 0.70 | 0.16 | (0.13, 0.21) | 3.40 |
$^{1}\mathrm{COI} =$ cutoff index
$^{2}\mathrm{SD} =$ standard deviation
$^{3}\mathrm{HSP} =$ Human serum pool
$^{4}\mathrm{PC1 / PC2} = \mathrm{PreciControl1 / PreciControl2}$
# b. Linearity/assay reportable range:
Not applicable; this is a qualitative assay.
# c. Traceability, Stability, Expected values (controls, calibrators, or methods):
# Calibrator
Calibrators are provided with the assay and are intended for the calibration of the Elecsys Syphilis immunoassay. The calibrator is referenced to a Roche internal reference standard. This internal reference standard is manufactured by dilution of high titer positive serum with nonreactive human serum.
# External Controls
The Elecsys Syphilis immunoassay controls are sold as an accessory to the test. The Negative Control is made from human serum shown to be non-reactive for antibodies to TP. The Positive Control is made from TP-non-reactive human serum spiked with high titer anti-TP reactive human serum. During the clinical study, the positive control was analyzed 270 times; the mean COI was 4.63 with a SD of 0.207.
# Sample Stability Studies
The stability of TP antibodies in serum, $\mathrm{K}_2$ -EDTA, $\mathrm{K}_3$ -EDTA, Li-Heparin, and CPDA plasma/Sodium-Citrate plasma was evaluated using eight different spiked samples (negative human serum spiked with varying levels of anti-TP antibodies). Reference samples, in their respective matrix, were stored at $-80^{\circ}\mathrm{C}$ for the duration of the experiment and then thawed and tested along with paired test samples for each storage condition. Recovery for samples stored under the test condition was determined by
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comparing the COI of the reference samples to the test samples. Acceptance criteria for recovery were:
- For reference COI < 1.0 deviation ± 0.2 COI
- For reference COI > 1.0 deviation ± 20% COI
Of the eight samples tested for each condition, three samples were prepared just below the cutoff for reactivity (COI < 1.0), three samples near the cutoff (COI = 1.0) and two samples were tested above the cutoff (COI > 1.0). All samples were tested in triplicate for a total of 24 tests per storage condition.
The stability of TP antibodies in various storage matrices was evaluated for:
- Refrigerated stability (at 2 to 8°C) for 21 days
- Room temperature stability (at 15 to 25°C) for 8 days
- Frozen stability (at -15 to -25°C) for 12 months
- Freeze/thaw stability after 5 cycles (a freeze/thaw cycle was defined as frozen at ≤ -10°C for > 12 hours)
All tests met the acceptance criteria for all the anti-coagulants and storage conditions tested. Roche is claiming the following storage conditions for specimens:
Serum, K₂-EDTA, K₃-EDTA, Li-Heparin, CPDA plasma, Sodium-Citrate plasma at:
- 2 to 8°C for 14 days
- 15 to 25°C for 5 days
- -15 to -25°C for 12 months
- Samples may be frozen and thawed up to 5 times
## Reagent Stability
To test reagent stability, a fresh reagent Rack-Pack was placed on the analyzer and calibrated. Reference values were determined and the kit was removed from the analyzer and stored at 2 to 8°C for 56 days. On days 28 and 56 the kit was placed on the analyzer, calibrated and samples were tested again. Eight spiked samples plus a positive and negative control were tested in duplicate both for the reference point and days 28 and 56. Of the eight samples tested, three samples were prepared just below the cutoff for reactivity (COI < 1.0), three samples near the cutoff (COI = 1.0) and two samples were tested above the cutoff (COI > 1.0). Acceptance criteria for recovery were:
- For reference COI < 1.0 deviation ± 0.2 COI
- For reference COI > 1.0 deviation ± 20% COI
All samples tested met the acceptance criteria. Roche has claimed reagent stability up to day 56 after opening a reagent Rack-Pack when the pack is kept at 2 to 8°C.
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# On-board Reagent Stability
The stability of Elecsys Syphilis reagent Rack-Pack left on the instrument was evaluated on days 0, 1, 8, 15, 22, and 30. Day 0 was used as the reference point to determine COI deviation. Eleven human serum samples plus two controls were evaluated on each day using the same reagents kept at 20 °C on-board the instrument. Calibration curves established for the previous time-point were used for days 8, 15, 22, and 30.
Acceptance criteria for recovery were:
- For reference COI < 1.0 deviation ± 0.2 COI
- For reference COI > 1.0 deviation ± 20% COI
All samples tested met the acceptance criteria. Roche has claimed 28 days in the package insert for on-board reagent stability.
# Shelf Life
The control reagent was measured after 7, 9, 13, 16, and 19 months storage at 2 to 8°C. Studies were performed with three lots of stored reagents and tested in duplicate for each lot. Percent recovery was calculated based on the target value of the Control Reagent. Acceptance criteria for recovery were:
- For reference COI < 1.0 deviation ± 0.2 COI
- For reference COI > 1.0 deviation ± 20% COI
The data demonstrated reagent stability for at least 18 months when stored at 2 to 8°C. Roche has indicated a 15 month shelf life for the control reagents.
# Calibrator Stability
Roche performed a calibration study using spiked human serum samples and fresh reagent kits on a single analyzer calibrated with a single lot of reagents. Recovery (% COI) was determined on days 28 and 56 and compared to the results obtained on day 0. Eight human serum samples plus controls were tested in duplicate. Acceptance criteria for recovery were:
- For reference COI < 1.0 deviation ± 0.2 COI
- For reference COI > 1.0 deviation ± 20% COI
All samples met the acceptance criteria on days 28 and 56. Roche is claiming a Calibrator stability of 28 days in the package insert.
# On-Board Calibrator Stability
The stability of Elecsys Syphilis calibrator left on the instrument was evaluated on days 0 and 8. Day 0 was used as the reference point to determine COI deviation. Eleven human
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serum samples plus two controls were evaluated in duplicate using the same reagents kept at 20 °C on-board the instrument. The calibration curve established on day 0 was used for the day 8 testing.
Acceptance criteria for recovery were:
- For reference COI < 1.0 deviation ± 0.2 COI
- For reference COI > 1.0 deviation ± 20% COI
All samples tested met the acceptance criteria. Roche has claimed seven days in the package insert for on-board calibrator stability.
## Hook Effect
The sponsor conducted a study to demonstrate that the Elecsys Syphilis immunoassay does not produce false non-reactive results when testing samples with high levels of anti-TP antibody. The study utilized six samples with medium to high levels of TP-antibody which were diluted with negative (TP-Ab non-reactive) serum. Each of the diluted samples was tested with the Elecsys Syphilis assay. Total RFU counts were plotted for each sample as a function of dilution level. Acceptance criterion set by Roche described the data as acceptable if there were no samples which resulted in a COI less than 3 due to high antibody concentration. The COI of undiluted serum samples ranged from 276 to 345.
The acceptance criteria were met in all samples tested. Plots of each sample dilution series supported the conclusion that there was no high dose hook effect. These data demonstrate that the Elecsys Syphilis assay is not susceptible to interference from specimens with high levels of anti-syphilis TP.
## Carryover
Previous carryover studies performed on the same instrument demonstrated the absence of carry-over on the cobas e 411 analyzer for other Elecsys assays. In addition, cobas e 411 analyzer utilizes disposable materials to reduce the probability of contamination due to carryover.
d. Detection limit:
Not applicable.
e. Analytical specificity:
### Interference by Endogenous Substances
Interference by endogenous substances was evaluated by testing three anti-T. pallidum antibody concentrations (negative, near cut-off and positive). Negative sample pools were prepared with an expected COI value between 0 and 1. Near cut-
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off sample pools were prepared such that the expected COI value was between 1.0 and 2.0. Positive sample pools were prepared with an expected COI of greater than 5.0. Each serum pool was spiked with the interferent at varying concentrations up to the maximum concentrations indicated in the table below. A total of 10 samples (ten 10-fold dilutions) were tested for each serum pool for each potential interferent. Recovery was calculated for the COI of each sample as the percent of the expected result (sample with no interferent present). Acceptance criteria for recovery were:
For reference $\mathrm{COI} < 1.0$ deviation $\pm 0.2$ COI
For reference $\mathrm{COI} > 1.0$ deviation $\pm 15\%$ COI
| Potential Interferent | Substance Measured up to | No Interference Seen up to | Label Claim |
| --- | --- | --- | --- |
| Intralipid (Lipemia) | 2000 mg/dL | 2000 mg/dL | 2000 mg/dL |
| Biotin | 70 ng/mL | 70 ng/mL | 60 ng/mL |
| Bilirubin | 66 mg/dL | 66 mg/dL | 66 mg/dL |
| Hemoglobin | 1000 mg/dL | 1000 mg/dL | 500 mg/dL |
| Rheumatoid Factor | 1500 IU/mL | 1500 IU/mL | 1500 IU/mL |
| Human Serum Albumin | 10 g/dL | 10 g/dL | 10 g/dL |
| Human IgG | 7.0 g/dL | 6.3 g/dL | 32 g/L |
| Human IgM | 1.0 g/dL | 1.0 g/dL | 10 g/L |
| Human IgA | 7.0 g/dL | 2.8 g/dL | 2.8 g/dL |
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# Drug Interference
Potential interference due to the presence of common pharmaceutical compounds was tested in a drug interference study. Human serum samples were spiked with anti-TP antibodies at high negative (COI < 1.0) or at low positive levels (COI < 2.0). These serum samples were tested in the presence or absence of sixteen commonly used pharmaceuticals. Absolute COI (for high negative samples) and % COI (for low positive samples) were compared to the reference COI to determine whether interference occurred. A list of the drugs and concentrations tested are shown in the table below. No interference was observed at the levels tested.
| Drug Tested | Concentrations Tested |
| --- | --- |
| Acetylcystein | 150 mg/L |
| Ampicillin-Na | 1000 mg/L |
| Ascorbic Acid | 300 mg/L |
| Cyclosporine | 5 mg/L |
| Cefoxitin | 2500 mg/L |
| Heparin | 5000 U/L |
| Levodopa | 20 mg/L |
| Methyldopa + 1.5 | 20 mg/L |
| Metronidazole | 200 mg/L |
| Phenylbutazone | 400 mg/L |
| Doxycyclin | 50 mg/L |
| Acetylsalicylic Acid | 1000 mg/L |
| Rifampicin | 60 mg/L |
| Acetaminophen | 200 mg/L |
| Ibuprofen | 500 mg/L |
| Theophylline | 100 mg/L |
# Cross-reactivity in Specimens with Medical Conditions not Related to Syphilis
Specimens from individuals diagnosed with other diseases were obtained from commercial vendors or were sourced from leftover clinical specimens. The presence of the given analyte (microorganism or antibody) was confirmed with an FDA-cleared assay. The specimens were tested by the Elecsys Syphilis assay. Positive samples were also tested by the BioRad Syphilis EIA II Total Antibody Assay. The results of the specificity study in samples from individuals with other diseases are shown below.
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| Potential Cross-reactant | Number Tested | Number of Positive Samples |
| --- | --- | --- |
| Borrelia | 50 | 0 |
| EBV IgG | 21 | 1 |
| Rubella IgG | 17 | 1 |
| E.coli antibodies | 18 | 1 |
| Hepatitis A | 25 | 1 |
| Hepatitis B | 10 | 2 |
| Hepatitis C | 13 | 0 |
| ANA^{1} | 15 | 1 |
| RF^{2} | 19 | 0 |
| HSV 1/2 | 12 | 1 |
| CMV IgG | 20 | 0 |
| HIV-1 | 25 | 1 |
| Toxoplasma IgG | 21 | 0 |
| Total | 266 | 9 |
¹ Anti-nuclear antigen
² Rheumatoid factor
The nine samples that were reactive with the Elecsys Syphilis assay were confirmed positive for anti-treponemal antibodies with the BioRad Syphilis EIA II Total Antibody Assay. The Elecsys Syphilis assay does not appear to cross-react with any of the analytes tested above.
f. Assay cut-off:
In order to define the cut-off for the Elecsys Syphilis assay, native human serum samples were measured with a prototype lot of the Elecsys Syphilis assay and a preliminary cut-off was set. Next, the Elecsys syphilis results from patient samples were compared to the results from other commercially available assays. The results of the subsequent multi-center clinical studies conducted in the EU and the US provided final validation for the cut-off value.
Result classification:
Sample result < 1.0 COI
Sample is interpreted as “non-reactive”
Sample result ≥ 1.0 COI
sample is interpreted as “reactive”
2. Comparison studies:
a. Method comparison with predicate device:
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The results of the Elecsys Syphilis assay were compared to a composite comparator based on an algorithm of results obtained from three commercially available syphilis assays: (a) a treponemal chemiluminescent immunoassay (Predicate), a nontreponemal assay (Rapid Plasma Reagin [RPR]), and a second treponemal assay (Treponema Pallidum Particle Agglutination [TP-PA]). Additional details of how the final comparator result was determined are provided below in the "Clinical Studies" section.
# b. Matrix comparison:
The effect of anticoagulants in the samples on the performance of the Elecsys Syphilis Immunoassay was determined by comparing values obtained from native samples spiked with anti- $T$ . pallidum antibodies (single donors) drawn into the following vacutainer tube types:
- Serum (plastic)-Used as the reference
- Serum separator tubes (SST)
- CPDA
- Dipotassium-EDTA plasma
- Tripotassium-EDTA plasma
- Lithium-Heparin plasma
Sodium-Citrate
- Dipotassium-EDTA plasma preparation tube (PPT)
A total of 57 serum/plasma pairs were tested for each anti-coagulant tube. The matrices were spiked with anti- $T$ . pallidum antibodies to produce samples ranging from below the COI cutoff (COI $< 1.0$ ) to high positive (COI $>10$ ). The panel also included many samples near the cutoff (COI close to 1.0). Recovery of the analyte as measured by COI or $\%$ COI in the presence of different anticoagulants was determined. Acceptance criteria for recovery were:
For reference COI $< 1.0$ deviation $\pm 0.2$ COI
For reference COI $>1.0$ deviation $\pm 20\%$ COI
| Matrix | Sample Size | Range | Maximum Deviation from Reference (%) | Maximum Absolute Deviation from Reference (COI) |
| --- | --- | --- | --- | --- |
| Serum | 57 | 0.130-62.8 | N/A | N/A |
| SST | 57 | 0.130-60.9 | 16% | 0.030 |
| K2-EDTA plasma | 57 | 0.130-66 | 9% | 0.040 |
| K3-EDTA plasma | 57 | 0.130-66.3 | 12% | 0.050 |
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| Li-Heparin plasma | 57 | 0.120-51.9 | 15% | 0.070 |
| --- | --- | --- | --- | --- |
| CPDA | 57 | 0.130-55.3 | 7% | 0.120 |
| Na-Citrate | 57 | 0.120-65.8 | 5% | 0.090 |
| K2-EDTA (PPT) | 57 | 0.130-70 | 12% | 0.070 |
The specifications were met for all anticoagulants. The resulting data support the package insert claim that serum, serum separation tubes, Li-Heparin plasma, $\mathrm{K}_2$ -EDTA- and $\mathrm{K}_3$ -EDTA-plasma, Na-citrate, CPDA plasma and $\mathrm{K}_2$ -EDTA (PPT) specimens are acceptable for use with the Elecsys Syphilis Immunoassay.
# 3. Clinical Studies:
A multicenter study was conducted from June 2014 to December 2014 (5 sites) and from August 2015 to November 2015 (4 sites) to evaluate the ability of the Elecsys Syphilis assay to detect antibodies (IgG and IgM) directed against Treponema pallidum (TP). A total of 2697 subjects were involved in the clinical study of which 37 did not meet the inclusion/exclusion criteria. The remaining 2660 specimens were tested in the Elecsys Syphilis Immunoassay clinical study. There were no samples excluded from the study after enrollment. The 2660 specimens consisted of 2282 specimens obtained through routine syphilis testing, 169 pre-selected samples presumed to be positive for antibodies directed against TP based on previous laboratory testing (including 15 pregnant women known to be reactive for syphilis antibodies), and 209 specimens from apparently healthy individuals. An additional 40 specimens from pregnant females negative for $T$ pallidum antibodies and spiked with individual high antibody-positive specimens were also tested in a separate study.
The 2660 specimens analyzed in the Elecsys Syphilis Immunoassay clinical study were collected at clinical sites in the following locations:
Miami, Florida: $6.84\%$
Spartanburg, North Carolina: $26.28\%$
Baltimore, Maryland: $21.95\%$
Minneapolis, Minnesota: $0.98\%$
Whittier, California: $29.14\%$
Miami Beach, Florida: $0.41\%$
Tamarac, Florida: $8.20\%$
Buenos Aires, Argentina: $5.64\%$
Nanikon, Switzerland: $0.56\%$
The clinical performance of the Elecsys Syphilis assay was evaluated by calculating positive percent agreement and negative percent agreement of the assay with the final comparator result based on an algorithm of results from three commercially available syphilis assays: an FDA-cleared treponemal chemiluminescent immunoassay
{15}
("Predicate"), a non-treponemal assay (Rapid Plasma Reagin [RPR]), and a second treponemal assay (Treponema Pallidum Particle Agglutination [TPPA]. Because the clinical diagnosis of syphilis must be supported by two reactive laboratory tests, consisting of a treponemal assay and a non-treponemal assay, or at least two treponemal assays, employing an algorithm of three syphilis tests to determine the comparator result presents information closest to the serological "truth."
The final comparator result was determined using a two out of three rule (Predicate, RPR, and TPPA). The table below shows how the final comparator result was interpreted for the Elecsys Syphilis assay clinical study.
| Treponemal (Predicate) | Non-treponemal (RPR) | 2ndTreponemal (TPPA) | Final Comparator Result |
| --- | --- | --- | --- |
| Negative | Negative | Positive | Negative |
| | | Negative | Negative |
| | | Inconclusive | Negative |
| Negative | Positive | Positive | Positive |
| | | Negative | Negative |
| | | Inconclusive | Negative |
| Positive | Positive | Positive | Positive |
| | | Negative | Positive |
| | | Inconclusive | Positive |
| Positive | Negative | Positive | Positive |
| | | Negative | Negative |
| | | Inconclusive | Negative |
| Indeterminate | Negative | Positive | Positive |
| | | Negative | Negative |
| | | Inconclusive | Indeterminate |
| Indeterminate | Positive | Positive | Positive |
| | | Negative | Negative |
| | | Inconclusive | Indeterminate |
# Clinical Performance in Prospectively Collected Specimens in the Intended Use Population
The 2282 prospectively collected specimens in the intended use population, analyzed in the Elecsys Syphilis assay clinical study consisted of 1524 specimens sent for routine syphilis testing (60% female, 40% male, 18-79 years old), 301 pregnant females (18-45 years old), and 457 HIV positive individuals (40% female, 60% male, 18-70 years old). Each of those specimens was analyzed with the Elecsys Syphilis assay and with the three reference assays.
{16}
A summary of the serological test profile for all prospectively-collected specimens in the intended use population is presented in the following table.
| Predicate Result | RPR | TPPA | Final Comparator Result | Elecsys Syphilis | Number of Subjects |
| --- | --- | --- | --- | --- | --- |
| NR^{1} | NR | N/A^{2} | Negative | NR | 2023 |
| NR | NR | Inconclusive | Negative | NR | 1 |
| NR | NR | NR | Negative | NR | 1 |
| NR | NR | NR | Negative | Reactive | 1 |
| NR | NR | Reactive | Negative | Reactive | 4 |
| NR | Reactive | NR | Negative | NR | 4 |
| Reactive | NR | Inconclusive | Negative | Reactive | 2 |
| Reactive | NR | NR | Negative | NR | 9 |
| Reactive | NR | NR | Negative | Reactive | 9 |
| Reactive | NR | Reactive | Positive | Reactive | 166 |
| Reactive | Reactive | N/A | Positive | Reactive | 62 |
¹ NR = Non-reactive
² N/A = Test not performed
The comparison between the Elecsys Syphilis assay result and the final comparator result for the prospectively-collected specimens in the intended use population is shown in the following table.
Percent Agreement in Prospective Specimens
| | Final Comparator Results | | |
| --- | --- | --- | --- |
| Elecsys Syphilis | Positive for Syphilis | Negative for Syphilis | Total |
| Reactive | 228 | 16 | 244 |
| Non reactive | 0 | 2038 | 2038 |
| Total | 228 | 2054 | 2282 |
Positive percent agreement for the Elecsys Syphilis assay in the prospective cohort was 100% (228/228) with a 95% confidence interval of 98.4% to 100.0%. Negative percent agreement was 99.2% (2038/2054) with a 95% confidence interval of 98.7% to 99.6%.
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Percent Agreement by Category for Prospective Specimens
| Cohort | Positive Percent Agreement | | PPA 95 % CI | Negative Percent Agreement | | NPA 95 % CI |
| --- | --- | --- | --- | --- | --- | --- |
| | % | Ratio | | % | Ratio | |
| Routine Syphilis | 100 | 66/66 | 94.56 to 100.00 | 99.8 | 1455/1458 | 99.40 to 99.96 |
| HIV | 100 | 162/162 | 97.75 to 100.00 | 95.6 | 282/295 | 92.58 to 97.63 |
| Pregnant | N/A | 0/0 | N/A | 100 | 301/301 | 98.78 to 100.00 |
| Total | 100 | 228/228 | 98.40 to 100.00 | 99.2 | 2038/2054 | 98.74 to 99.55 |
## Clinical Performance in Retrospective Samples (Pre-selected)
Clinical performance in the pre-selected retrospective cohort was evaluated by testing a total of 169 specimens, including 15 pregnant positive women and 154 subjects medically diagnosed with syphilis at different stages. The comparison between the Elecsys Syphilis results and the final comparator results is shown in the following table.
| | Final Comparator Results | | |
| --- | --- | --- | --- |
| Elecsys Syphilis | Positive for Syphilis | Negative for Syphilis | Total |
| Reactive | 155 | 0 | 155 |
| Non-reactive | 2 | 12 | 14 |
| Total | 157 | 12 | 169 |
Positive percent agreement for the Elecsys Syphilis assay in the retrospective cohort was 98.7% (155/157) with a 95% confidence interval of 95.5% to 99.85%. Negative percent agreement was 100.0% (12/12) with a 95% confidence interval of 73.5% to 100.0%
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Percent Agreement by Category for Retrospective Specimens
| Category | Positive Percent Agreement | | PPA 95 % CI | Negative Percent Agreement | | NPA 95 % CI |
| --- | --- | --- | --- | --- | --- | --- |
| | % | Ratio | | % | Ratio | |
| Pregnant (Retrospective) | 100 | 15/15 | 78.20 to 100.00 | N/A | 0/0 | N/A |
| Staged | 98.6 | 140/142 | 95.00 to 99.83 | 100 | 12/12 | 73.54 to 100.00 |
| Overall (Retrospective) | 98.7 | 155/157 | 95.47 to 99.85 | 100 | 12/12 | 73.54 to 99.55 |
Clinical Performance in Medically Diagnosed Individuals
Samples were collected from 154 individuals diagnosed with primary, secondary or latent syphilis. They included 10 females and 144 males. Results of the Elecsys Syphilis assay for this cohort are summarized below.
Reactivity of the Elecsys Syphilis Assay in Subjects Medically Diagnosed with Syphilis
| Medically Diagnosed Individuals | | | Elecsys Syphilis Result | |
| --- | --- | --- | --- | --- |
| Syphilis Stage | Treatment Status | N | Reactive | Nonreactive |
| Primary | Treated | 29 | 16 | 13* |
| | Untreated | 25 | 25 | 0 |
| Secondary | Treated | 25 | 24 | 1 |
| | Untreated | 25 | 25 | 0 |
| Latent | Treated | 25 | 25 | 0 |
| | Untreated | 25 | 25 | 0 |
* 12 of these samples also tested negative for Syphilis with the composite testing algorithm
Clinical Performance in Pregnant Females
A total of 316 pregnant female samples were tested in the study. Of these, 301 were prospectively collected and 15 were retrospectively collected. The percent agreement between the Elecsys Syphilis results and the final comparator results is shown below, stratified by pregnancy trimesters compared with the Composite Algorithm for pregnant women.
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Percent Agreement in Pregnant Women
| Category | PPA | | PPA 95% CI | NPA | | NPA 95% CI |
| --- | --- | --- | --- | --- | --- | --- |
| | % | Ratio | | % | Ratio | |
| Pregnant (Prospective) | N/A | 0/0 | N/A | 100 | 301/301 | 98.8-100.0 |
| 1^{st} Trimester | N/A | 0/0 | N/A | 100 | 100/100 | 96.4-100.0 |
| 2^{nd} Trimester | N/A | 0/0 | N/A | 100 | 125/125 | 97.1-100.0 |
| 3^{rd} Trimester | N/A | 0/0 | N/A | 100 | 76/76 | 95.3-100.0 |
| Pregnant (Retrospective) | 100 | 15/15 | 78.2–100.0 | N/A | 0/0 | N/A |
| 1^{st} Trimester | 100 | 7/7 | 59.0-100.0 | N/A | 0/0 | N/A |
| 3^{rd} Trimester | 100 | 8/8 | 63.1-100.0 | N/A | 0/0 | N/A |
In addition, 40 specimens from nonreactive pregnant females, spiked with samples known to be highly reactive for TP antibodies, were analyzed with the Elecsys Syphilis assay. All samples tested reactive.
Clinical Performance in Apparently Healthy Individuals
Specimens were collected from 209 apparently healthy individuals. Of these, 80 were female and 129 male. The results of the Elecsys Syphilis assay for this group are shown below.
| | Elecsys Syphilis Result | | |
| --- | --- | --- | --- |
| | # Reactive | # Non-reactive | |
| Female | 9 (11.3%) | 71 (88.7%) | 80 |
| Male | 11 (8.5%) | 118 (91.5%) | 129 |
| Total | 20 (9.6%) | 189 (90.4%) | 209 |
a. Clinical Sensitivity:
The clinical sensitivity of the assay was expressed as percent agreement of the Elecsys Syphilis assay results with the final comparator result, as explained above.
b. Clinical specificity:
The clinical specificity of the assay was expressed as percent agreement of the Elecsys Syphilis assay results with the final comparator result, as explained above.
c. Other clinical supportive data (when a. and b. are not applicable):
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There were no invalid results recorded by the Elecsys Syphilis Immunoassay during the clinical study.
# 4. Clinical cut-off:
Not applicable.
# 5. Expected values/Reference range:
In this clinical study there were 2282 prospectively collected specimens for the intended use population that were tested with the Elecsys Syphilis assay. There were 244 reactive samples for a $10.7\%$ prevalence of $T.$ pallidum antibodies in the study population. The distribution of the Elecsys Syphilis reactive and non-reactive results is summarized below by age and gender.
| | | Elecsys Syphilis Results | | |
| --- | --- | --- | --- | --- |
| Age Range (years) | Gender | Reactive | Non-reactive | Total |
| 18-21 | Female | 0 (0.00%) | 247 (100%) | 247 |
| | Male | 6 (3.5%) | 165 (96.5%) | 171 |
| 22-29 | Female | 0 (0.00%) | 358 (100%) | 358 |
| | Male | 19 (10.7%) | 159 (89.3%) | 178 |
| 30-39 | Female | 10 (3.7%) | 261 (96.3%) | 271 |
| | Male | 13 (12.3%) | 93 (87.7%) | 106 |
| 40-49 | Female | 29 (12.1%) | 210 (87.9%) | 239 |
| | Male | 29 (20.0%) | 116 (80.0%) | 145 |
| 50-59 | Female | 47 (20.8%) | 179 (79.2%) | 226 |
| | Male | 55 (27.1%) | 148 (72.9%) | 203 |
| 60-69 | Female | 11 (23.9%) | 35 (76.1%) | 46 |
| | Male | 23 (29.5%) | 55 (70.5%) | 78 |
| 70-79 | Female | 0 (0.00%) | 5 (100%) | 5 |
| | Male | 2 (22.2%) | 7 (77.8%) | 9 |
| Combined | Total | 244 (10.7%) | 2038 (89.3%) | 2282 |
# N. Instrument Name:
cobas e 411 Analyzer
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O. System Descriptions:
The Elecsys Syphilis Immunoassay is performed on the cobas e 411 analyzer using previously cleared software. The software version has been updated to include the Elecsys Syphilis test to the test menu.
1. Modes of Operation:
This is a fully automated immunoassay analyzer.
Does the applicant’s device contain the ability to transmit data to a computer, webserver, or mobile device?
Yes ☑ or No ☐
Does the applicant’s device transmit data to a computer, webserver, or mobile device using wireless transmission?
Yes ☐ or No ☑
2. Software:
The latest Elecsys Syphilis Immunoassay is performed on the cobas e 411 analyzer using software version 02-04.
FDA has reviewed applicant’s Hazard Analysis and software development processes for this line of product types:
Yes ☑ or No ☐
3. Specimen Identification:
The specimens are identified by an internal barcode reader.
4. Specimen Sampling and Handling:
The specimen processing is automated. The operator only needs to place the primary sample tube in the instrument sample carrier (disk or rack systems).
5. Calibration:
Assays do not need to be calibrated every time they are run; however, certain variables make recalibration necessary. Calibration must be performed when a new reagent lot is used, when documentation accompanying a new version of an existing assay states that calibration is required, and when the controls are out of range.
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6. Quality Control:
Quality control is performed using the Elecss PreciControl Syphilis Cal1 and Syphilis Cal2. The positive control (inactivated) is reactive for anti-TP. Controls are not barcode labeled and need to be run like external controls.
P. Other Supportive Instrument Performance Characteristics Data Not Covered In The "Performance Characteristics" Section above:
Not applicable.
Q. Proposed Labeling:
The labeling is sufficient and it satisfies the requirements of 21 CFR Part 809.10.
R. Conclusion:
The submitted information in this premarket notification is complete and supports a substantial equivalence decision.
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