Elecsys FT4 III

K181233 · Roche Diagnostics · CEC · Sep 18, 2018 · Clinical Chemistry

Device Facts

• Record ID: K181233
• Device Name: Elecsys FT4 III
• Applicant: Roche Diagnostics
• Product Code: CEC · Clinical Chemistry
• Decision Date: Sep 18, 2018
• Decision: SESE
• Submission Type: Traditional
• Regulation: 21 CFR 862.1695
• Device Class: Class 2

Indications for Use

Assay for the in vitro quantitative determination of free thyroxine in human serum and plasma. Measurements obtained by this device are used in the diagnosis and treatment of thyroid diseases. The electrochemiluminescence immunoassay "ECLIA" is intended for use on the cobas e 411 immunoassay analyzer.

Device Story

Elecsys FT4 III is an in vitro diagnostic immunoassay for quantitative measurement of free thyroxine (fT4) in human serum and plasma. It utilizes electrochemiluminescence immunoassay (ECLIA) technology on the cobas e 411 analyzer. The assay uses streptavidin-coated microparticles, biotinylated T4, and ruthenium-labeled anti-T4 antibodies. The device measures light signals generated during the electrochemical reaction to determine fT4 concentration. It is operated by laboratory professionals in clinical settings. Results assist physicians in diagnosing and managing thyroid disorders. The device is a modification of the predicate Elecsys FT4 II, specifically optimized with reduced D-biotin concentration in the R2 reagent buffer to improve biotin interference resistance. It provides clinicians with quantitative data to assess thyroid function.

Clinical Evidence

Bench testing only. Precision evaluated per CLSI EP05-A2 (n=84 per sample, CVs 1.7-10.7%). Linearity assessed per CLSI EP06-A (R²=0.9988). LoB (0.03 ng/dL), LoD (0.05 ng/dL), and LoQ (0.101 ng/dL) determined per CLSI EP17-A2. Method comparison with predicate (n=141) showed high correlation (r=0.999). Interference testing confirmed robustness against endogenous substances and common drugs, with specific limitations noted for biotin, thyroid drugs, and autoantibodies.

Technological Characteristics

Quantitative electrochemiluminescent immunoassay (ECLIA). Components: Streptavidin-coated microparticles, ruthenium-labeled polyclonal anti-T4 antibody, biotinylated T4. Instrument: Roche cobas e 411. Measuring range: 0.101–7.7 ng/dL. Traceable to Enzymun Test (standardized via equilibrium dialysis).

Indications for Use

Indicated for in vitro quantitative determination of free thyroxine in human serum and plasma to aid in the diagnosis and treatment of thyroid disease. Intended for use on the cobas e 411 immunoassay analyzer.

Regulatory Classification

Identification

A free thyroxine test system is a device intended to measure free (not protein bound) thyroxine (thyroid hormone) in serum or plasma. Levels of free thyroxine in plasma are thought to reflect the amount of thyroxine hormone available to the cells and may therefore determine the clinical metabolic status of thyroxine. Measurements obtained by this device are used in the diagnosis and treatment of thyroid diseases.

Predicate Devices

• Elecsys FT4 II Assay (k131244)

Submission Summary (Full Text)

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# 510(k) SUBSTANTIAL EQUIVALENCE DETERMINATION DECISION SUMMARY ASSAY ONLY TEMPLATE

A. 510(k) Number:
k181233

B. Purpose for Submission:
Modification of a previously cleared assay (k131244)

C. Measurand:
Free thyroxine (Free T4)

D. Type of Test:
Quantitative, electrochemiluminescent immunoassay

E. Applicant:
Roche Diagnostics

F. Proprietary and Established Names:
Elecsys FT4 III

G. Regulatory Information:
1. Regulation section:
21 CFR 862.1695
2. Classification:
Class II
3. Product code:
CEC
4. Panel:
Chemistry (75)

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H. Intended Use:

1. Intended use(s):

Refer to Indications for Use below

2. Indication(s) for use:

Assay for the in vitro quantitative determination of free thyroxine in human serum and plasma. Measurements obtained by this device are used in the diagnosis and treatment of thyroid diseases.

The electrochemiluminescence immunoassay "ECLIA" is intended for use on the cobas e 411 immunoassay analyzer.

3. Special conditions for use statement(s):

For in vitro diagnostic use only
For prescription use only

4. Special instrument requirements:

Roche cobas e411 Analyzer

I. Device Description:

The Elecsys FT4 III assay contains the following components:

M: Streptavidin-coated microparticles (transparent cap), 1 bottle, 12 mL: Streptavidin-coated microparticles 0.72 mg/mL; preservative.

R1: Anti T4-Ab~Ru(bpy) (gray cap), 1 bottle, 18 mL: Polyclonal anti T4 antibody (sheep) labeled with ruthenium complex 75 ng/mL; phosphate buffer 100 mmol/L, pH 7.0; preservative.

R2: T4~biotin (black cap), 1 bottle, 18 mL: Biotinylated T4 2.5 ng/mL; free D-biotin 8 ng/mL; phosphate buffer 100 mmol/L, pH 7.0; preservative.

J. Substantial Equivalence Information:

1. Predicate device name(s):

Elecsys FT4 II Assay

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2. Predicate 510(k) number:

k131244

3. Comparison with predicate:

Elecsys FT4 II assay

| Similarities | | |
| --- | --- | --- |
| Item | New Device Elecsys FT4 III (k181233) | Predicate Elecsys FT4 II (k131244) |
| Intended Use | Quantitative determination of free thyroxine (FT4) in serum and plasma | Same |
| Methodology | Quantitative electrochemiluminescence immunoassay | Same |
| Sample Volume | 15 μL | Same |
| Calibrators | 2 levels | Same |
| Assay Time | 18 minutes | Same |
| Sample type | Serum and plasma (Li-heparin, K2-EDTA, K3-EDTA) | Same |
| Measuring Range | 0.101-7.77 ng/dL | Same |
| LoB | 0.03 ng/dL | Same |
| LoD | 0.05 ng/dL | Same |
| LoQ | 0.101 ng/dL | Same |
| Differences | | |
| --- | --- | --- |
| Item | New Device Elecsys FT4 III (k181233) | Predicate Elecsys FT4 II (k131244) |
| Biotin | D-Biotin concentration in the R2 reagent buffer: 8 ng/mL | D-Biotin concentration in the R2 reagent buffer: 50 ng/mL |
| Instrument Platform | cobas e 411 | Elecsys and cobas e |

# K. Standard/Guidance Document Referenced (if applicable):

CLSI EP05-A2: Evaluation of Precision Performance of Quantitative Measurement Methods: Approved Guideline, Second Edition

CLSI EP06-A: Evaluation of the Linearity of Quantitative Measurement Procedures: A statistical Approach: Approved Guideline

CLSI EP17-A2, Evaluation of Detection Capability for Clinical Laboratory Measurement Procedures: Approved Guideline, Second Edition

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L. Test Principle:

This is a competitive assay with an assay time of 18 minutes.

First incubation: 15 μL of sample is combined with a T4 specific antibody labeled with a sulfonyl ruthenium complex.

Second incubation: After addition of biotinylated T4 and streptavidin-coated microparticles, the still free binding sites of the labeled antibody become occupied, with formation of an antibody hapten complex. The entire complex becomes bound to the solid phase via interaction of biotin and streptavidin.

The reaction mixture is then aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Unbound substances are then removed with ProCell/ProCell M. Application of a voltage to the electrode then induces chemiluminescent emission which is measured by a photomultiplier.

Results are determined via a calibration curve which is instrument-specifically generated by 2 point calibration and a master curve provided via the reagent barcode.

M. Performance Characteristics (if/when applicable):

1. Analytical performance:

a. Precision/Reproducibility:

The repeatability (within-run) and intermediate precision (total) of the Elecsys FT4 III assay were evaluated on one cobas e 411 Immunoassay Analyzer referencing the CLSI EP05-A2 guideline. Five human serum samples and two levels of control material were analyzed. The protocol consisted of testing 2 replicates of each human serum sample and control per run, 2 runs per day for 21 days.

The results of the precision study were as follows:

| Sample | n | Mean (ng/dL) | Repeatability | | Intermediate precision | |
| --- | --- | --- | --- | --- | --- | --- |
| | | | SD (ng/dL) | CV (%) | SD (ng/dL) | CV (%) |
| Human serum 1 | 84 | 0.120 | 0.007 | 5.7 | 0.013 | 10.7 |
| Human serum 2 | 84 | 1.05 | 0.019 | 1.8 | 0.037 | 3.5 |
| Human serum 3 | 84 | 1.86 | 0.032 | 1.7 | 0.057 | 3.0 |
| Human serum 4 | 84 | 4.49 | 0.086 | 1.9 | 0.176 | 3.9 |
| Human serum 5 | 84 | 7.15 | 0.174 | 2.4 | 0.423 | 5.9 |
| PC Universal 1 | 84 | 1.23 | 0.020 | 1.6 | 0.037 | 3.0 |
| PC Universal 2 | 84 | 3.19 | 0.067 | 2.1 | 0.108 | 3.4 |

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b. Linearity/assay reportable range:

Linearity of the Elecsys FT4 III assay was assessed using human serum samples on the cobas e 411 immunoassay analyzer according to CLSI EP06-A guideline. A high analyte human serum sample was diluted with FT4 analyte free human serum to create 8 levels with FT4 concentrations from 0.068 to 8.623 ng/dL. Each sample was measured in triplicate on 3 lots of reagent. Linearity was evaluated using first, second and third polynomial regression analysis based on CLSI EP06-A. The coefficient of the third order polynomial regression was found to be significant; therefore, calculation of the third order model was used to demonstrate linearity. All three reagent lots generated similar results and one representative lot is presented below.

The linear regression line was y = 0.982x + 0.009, R²=0.9988

Summary of the deviation of the third order polynomial regression against the expected linear regression:

| Sample | Expected (ng/dL) | Linear regression (ng/dL) | 3^{rd} Order (ng/dL) | Absolute Difference (ng/dL) | Relative difference (%) |
| --- | --- | --- | --- | --- | --- |
| 1 | 0.068 | 0.075 | 0.071 | -0.004 | -5.91 |
| 2 | 0.134 | 0.141 | 0.141 | 0.000 | 0.244 |
| 3 | 0.270 | 0.273 | 0.282 | 0.009 | 3.2 |
| 4 | 0.538 | 0.538 | 0.558 | 0.021 | 3.83 |
| 5 | 1.080 | 1.064 | 1.095 | 0.027 | 2.52 |
| 6 | 2.152 | 2.121 | 2.113 | -0.014 | -0.678 |
| 7 | 4.312 | 4.234 | 4.055 | -0.184 | -4.35 |
| 8 | 8.623 | 8.468 | 8.623 | 0.147 | 1.73 |

The results of the linearity study and the limit of detection study (below) support the sponsor claims that the measuring range of this assay is 0.101 – 7.7 ng/dL.

c. Traceability, Stability, Expected values (controls, calibrators, or methods):

Traceability:

The Elecsys FT4 III assay is traceable to the Enzymun Test which was standardized using equilibrium dialysis.

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# d. Detection limit:

The limit of blank (LoB) is the 95th percentile value from 60 measurements of analyte-free samples over several independent series (60 measurements /lot, 3 lots of regents). The LoB corresponds to the concentration below which analyte-free samples are found with a probability of $95\%$ and was determined to be $0.03\mathrm{ng / dL}$ (highest of the 3 lots).

The limit of detection (LoD) is determined based on the LoB and the standard deviation of low concentration samples. The LoD corresponds to the lowest analyte concentration which can be detected (value above the LoB with a probability of $95\%$ ). Five level of low samples were measured in two replicates per sample per run for 6 runs (one run per day, over multiple days), using 3 lots of reagents. LoD was determined to be $0.05\mathrm{ng / dL}$ (highest of the 3 lots).

The limit of quantitation (LoQ) was determined by measuring five low serum samples, in five replicates per run, one run per day, over 5 days, using 3 lots of reagents. LoQ is defined as the lowest analyte concentration that can be reproducibly measured with an intermediate precision CV of $\leq 20\%$ and was determined to be $0.101\mathrm{ng / dL}$ (highest of the 3 lots).

The claimed measuring range of this assay is: $0.101 - 7.7\mathrm{ng / dL}$

# e. Analytical specificity:

# 1. Endogenous substances

The effect of endogenous substances was evaluated on the e 411 Analyzer using pooled human serum samples spiked with L-Thyroxine. For each potential interferent, three serum samples containing low, mid, and high concentrations of FT4 were analyzed. For all substances tested, no significant interference was defined as recovery $\pm 10\%$ of initial value. The potential interferents and the highest concentration tested which did not cause significant interference are listed below:

| Potential interferent | Highest concentration at which no interference was observed |
| --- | --- |
| Bilirubin | 66 mg/dL |
| Hemoglobin | 1.0 g/dL |
| Lipemia (Intralipid) | 2000 mg/dL |
| Rheumatoid Factors | 1500 IU/mL |
| IgG | 7.0 g/dL |
| IgA | 1.6 g/dL |
| IgM | 1.0 g/dL |

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2. Structurally similar substances

The effect of structurally similar substances was determined using human serum samples spiked with potential cross-reactant compounds and analyzed in duplicate on the e 411 Analyzer. For all substances tested, no significant interference was defined as recovery ± 10% of initial value. The following cross-reactivities were found at FT4 concentrations of approximately 0.974 ng/dL and 2.66 ng/dL:

| Cross-reactant | Concentration tested (ng/dL) | Cross-reactivity % |
| --- | --- | --- |
| L-T3 | 50000 | 0.005 |
| D-T3 | 50000 | 0.002 |
| rT3 | 190000 | 0.007 |
| 3-iodo-L-tyrosine | 10000000 | 0.000 |
| 3,5-diiodo-L-tyrosine | 10000000 | 0.000 |
| 3,3',5-triiodothyroacetic acid | 100000 | 0.000 |
| 3,3',5,5'-tetraiodothyroacetic acid | 100000 | 0.001 |

3. Common drugs

The effect of common therapeutic drugs and thyroid drugs was evaluated on the e 411 Analyzer using human serum pools spiked with L-Thyroxine. For each drug, two serum samples containing a low and high concentration of FT4 were analyzed. For all substances tested, no significant interference was defined as recovery ± 10% of initial value. The drugs and the highest concentration tested which did not cause significant interference are listed below.

| Drug | Highest concentration at which no interference was observed |
| --- | --- |
| Acetaminophen | 200 μg/mL |
| Acetylcysteine | 1660 μg/mL |
| Acetylsalicylic Acid | 300 μg/mL |
| Amiodarone | 200 μg/mL |
| Ampicillin-Na | 1000 μg/mL |
| Ascorbic acid | 300 μg/mL |
| Carbimazole | 6.0 μg/mL |
| Cefoxitin | 2500 μg/mL |
| Cyclosporine | 5 μg/mL |
| Doxycycline | 50 μg/mL |
| Fluocortolone | 100 μg/mL |
| Heparin | 5000 U |
| Hydrocortisone | 200 μg/mL |
| Ibuprofen | 50 μg/mL |

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| Drug | Highest concentration at which no interference was observed |
| --- | --- |
| Iodide | 0.2 μg/mL |
| Levodopa | 20 μg/mL |
| Methyldopa | 20 μg/mL |
| Metronidazole | 200 μg/mL |
| Octreotide | 0.3 μg/mL |
| Perchlorate | 2000 μg/mL |
| Phenylbutazone | 100 μg/mL |
| Prednisolone | 100 μg/mL |
| Propranolol | 240 μg/mL |
| Propylthiouracil | 300 μg/mL |
| Rifampicin | 60 μg/mL |
| Theophylline | 100 μg/mL |
| Thiamazole | 80 μg/mL |

Thyroid drugs Furosemide and Levothyroxine caused elevated Free T4 findings at the daily therapeutic dosage level. This is indicated in the labeling.

The sponsor has the following limitation statement in the labeling:

Any influence that might affect the binding behavior of the binding proteins can alter the result of the FT4 tests (e.g. drugs, NTIs (Non Thyroid Illness)), patients suffering from FDH (Familial Dysalbuminemic Hyperthyroxinemia).

The test cannot be used in patients receiving treatment with lipid-lowering agents containing D-T4. If the thyroid function is to be checked in such patients, the therapy should first be discontinued for 4-6 weeks to allow the physiological state to become re-established.

Autoantibodies to thyroid hormones can interfere with the assay.

## 4. Biotin interference:

Biotin interference was tested up to 1200 ng/mL in serum samples at low, medium and high concentrations of FT4. Interference was defined as a difference >±10% of the control sample values. The results are summarized in the tables below:

| % Bias for samples containing various concentrations of Biotin | | | | | |
| --- | --- | --- | --- | --- | --- |
| Sample ng/dL | Biotin concentrations (ng/mL) | | | | |
| | 52 | 65 | 78 | 91 | 104 |
| 0.96 | 1.2 | 2.1 | 3.6 | 5.7 | 8.5 |
| 1.66 | -1.8 | -1.4 | 1.3 | 3.0 | 7.3 |
| 2.61 | -0.5 | 0.6 | 2.3 | 4.7 | 7.5 |

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| % Bias for samples containing various concentrations of Biotin | | | | | |
| --- | --- | --- | --- | --- | --- |
| Sample ng/dL | Biotin concentrations (ng/mL) | | | | |
| | 117 | 150 | 300 | 600 | 1200 |
| 0.96 | 10.9 | 17.6 | 57.1 | 256 | * |
| 1.66 | 7.6 | 16.1 | 53.7 | 291 | * |
| 2.61 | 9.7 | 15.9 | 56.5 | * | * |
| * Values above the measuring range. % Bias cannot be calculated. | | | | | |

The labeling states:

Specimens with biotin concentrations up to 104 ng/mL demonstrated ≤ 10% bias in results. Biotin concentrations greater than 104 ng/mL can lead to falsely increased fT4 results. Some studies have shown that serum concentrations of biotin can reach 355 ng/mL within the first hour after biotin ingestion for subjects consuming supplements of 20 mg biotin per day and up to 1160 ng/mL for subjects after a single dose of 300 mg biotin. Do not test samples from patients who take biotin.

f. Assay cut-off:

Not applicable

2. Comparison studies:

a. Method comparison with predicate device:

A method comparison study was performed with 141 human serum samples (138 native, 3 spiked) with concentrations ranging from 0.18 to 7.14 ng/dL. The comparison of the Elecsys FT4 III assay (y) with the predicate device, Elecsys FT4 II assay (x), produced the following results:

Linear regression y = 1.02x + 0.047 r = 0.999

Passing-Bablok y = 1.03x + 0.014 r = 0.957

b. Matrix comparison:

A total of 53 serum/plasma pairs per sample material were tested in singleton with one reagent lot on one cobas e 411 immunoassay analyzer. Serum concentrations ranged from 0.155 – 7.72 ng/dL.

The Passing-Bablok regression results are the following:

Serum/Li-Heparin: y=1.03x-0.017, r=0.999

Serum/K2-EDTA: y= 1.01x-0.10, r=0.999

Serum /K3 EDTA: y=1.03x-0.035, r=0.999

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The results of the study support the sponsor claims that K2-EDTA, K3-EDTA, and lithium heparin plasma are acceptable anti-coagulants for the FT4 III assay.

3. Clinical studies:
a. Clinical Sensitivity:
Not applicable
b. Clinical specificity:
Not applicable
c. Other clinical supportive data (when a. and b. are not applicable):
Not applicable

4. Clinical cut-off:
Not applicable

5. Expected values/Reference range:
Euthyroid: 0.93 1.7 ng/dL

These values correspond to the 2.5th and 97.5th percentile of results from a total of 801 healthy test subjects studied.

N. Proposed Labeling:
The labeling is sufficient and it satisfies the requirements of 21 CFR Parts 801 and 809, as applicable.

O. Conclusion:
The submitted information in this premarket notification is complete and supports a substantial equivalence decision.

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