TOX A/B QUICK CHEK

K050891 · Techlab, Inc. · LLH · Jul 25, 2005 · Microbiology

Device Facts

• Record ID: K050891
• Device Name: TOX A/B QUICK CHEK
• Applicant: Techlab, Inc.
• Product Code: LLH · Microbiology
• Decision Date: Jul 25, 2005
• Decision: SESE
• Submission Type: Traditional
• Regulation: 21 CFR 866.2660
• Device Class: Class 1

Indications for Use

The TOX A/B QUIK CHEK™ test is a rapid immunoassay for detecting Clostridium difficile toxins A and B in fecal specimens from persons suspected of having C. difficile disease. The test is to be used as an aid in the diagnosis of C. difficile disease and results should be considered in conjunction with the patient history.

Device Story

TOX A/B QUIK CHEK™ is a rapid membrane-based immunoassay for qualitative detection of C. difficile toxins A and B in fecal specimens. Device utilizes antibodies specific to toxins A and B immobilized on a reaction membrane. Fecal sample is diluted and mixed with horseradish peroxidase-conjugated anti-toxin antibodies; mixture is added to sample well. During 15-minute incubation, toxin-antibody-conjugate complexes form and migrate to the membrane, where they are captured by immobilized antibodies. After washing and substrate addition, presence of blue line at 'T' position indicates positive result; blue line at 'C' position confirms proper reagent activity and migration. Performed by laboratory personnel. Results interpreted visually by clinician to aid in diagnosis of C. difficile disease in conjunction with patient history. Benefits include rapid identification of toxigenic C. difficile, facilitating timely clinical management.

Clinical Evidence

Clinical performance evaluated across 5 studies (n=842) comparing TOX A/B QUIK CHEK™ to tissue culture assay. Results: 90.2% sensitivity (95% CI: 84.1-94.2%), 99.7% specificity (95% CI: 98.8-99.9%), 98.6% PPV, 97.9% NPV, and 98.0% correlation. Reproducibility confirmed at 3 laboratories over 3 days with 100% agreement on known positive and negative samples.

Technological Characteristics

Rapid membrane immunoassay. Components: immobilized anti-toxin A/B antibodies (test line), anti-IgG antibodies (control line), and horseradish peroxidase-conjugated anti-toxin A/B antibodies. Visual readout via blue line appearance. Analytical sensitivity: 0.63 ng/mL (toxin A), 1.25 ng/mL (toxin B). No software or electronic components.

Indications for Use

Indicated for detection of C. difficile toxins A and B in fecal specimens from patients suspected of having C. difficile disease; aid in diagnosis; results to be used with patient history.

Regulatory Classification

Identification

A microorganism differentiation and identification device is a device intended for medical purposes that consists of one or more components, such as differential culture media, biochemical reagents, and paper discs or paper strips impregnated with test reagents, that are usually contained in individual compartments and used to differentiate and identify selected microorganisms. The device aids in the diagnosis of disease.

Predicate Devices

• Premier toxins A & B (K993914)
• ImmunoCard Toxins A & B (K041003)
• C. difficile TOX A/B II (K00306)
• ProSpecT C. difficile toxin A/B (K033479)
• X/pect C. difficile toxin A/B (K041951)

Submission Summary (Full Text)

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

A. 510(k) Number:
K050891

B. Purpose for Submission:
Substantial equivalence determination

C. Measurand:
Clostridium difficile toxins A and B

D. Type of Test:
A qualitative rapid immunoassay

E. Applicant:
TechLab Inc.

F. Proprietary and Established Names:
TOX A/B Quik Chek

G. Regulatory Information:
1. Regulation section:
21 CFR Part 866.2660 Microorganism Differentiation and Identification
2. Classification:
I
3. Product code:
LLH – Reagents, Clostridium difficile toxin
4. Panel:
Microbiology (83)

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H. Intended Use:

1. Intended use:

The TOX A/B QUIK CHEK™ test is a rapid immunoassay for detecting Clostridium difficile toxins A and B in fecal specimens from persons suspected of having C. difficile disease. The test is to be used as an aid in the diagnosis of C. difficile disease and results should be considered in conjunction with the patient history.

2. Indication for use:

The TOX A/B QUIK CHEK™ test is a rapid immunoassay for detecting Clostridium difficile toxins A and B in fecal specimens from persons suspected of having C. difficile disease. The test is to be used as an aid in the diagnosis of C. difficile disease and results should be considered in conjunction with the patient history.

3. Special conditions for use statement:

For prescription use only

4. Special instrument requirements:

Not applicable

I. Device Description:

The TOX A/B QUIK CHEK™ uses antibodies specific for toxins A and B of C. difficile. The device contains a Reaction Window with two vertical lines of immobilized antibodies. The test line (“T”) contains antibodies against C. difficile toxins A and B. The control line (“C”) contains anti-IgG antibodies. The Conjugate consists of antibodies to toxins A and B coupled to horseradish peroxidase. The kit contains:

Membrane Devices –25 pouches, each containing 1 device and a desiccant pack
Diluent (14 mL) – Buffered protein solution containing 0.02% thimerosal
Wash Buffer (10 mL) – A buffered solution containing 0.02% thimerosal
Substrate (3.5 mL) – Solution containing tetramethylbenzidine
Conjugate (2 mL) – Mouse monoclonal antibody specific for toxin A coupled to horseradish peroxidase and goat polyclonal antibody specific for toxin B coupled to horseradish peroxidase in a buffered protein solution containing 0.02% thimerosal
Positive Control (1 mL) – Antigen in a buffered protein solution

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J. Substantial Equivalence Information:

1. Predicate device names:
Premier toxins A & B, ImmunoCard Toxins A & B, C. difficile TOX A/B II, ProSpecT C. difficile toxin A/B, X/pect C. difficile toxin A/B

2. Predicate 510(k) numbers:
K993914, K041003, K00306 and K030404, K033479 and K041951

3. Comparison with predicate:
| Similarities | | |
| --- | --- | --- |
| Item | Device | Predicate |
| Intended Use | Detection of C.difficile toxins in fecal specimens | Same |
| Specimen type | Human stool | Same |
| Technology | Enzyme immunoassay | Same |
| | | |
| Differences | | |
| --- | --- | --- |
| Item | Device | Predicate |
| Limit of detection | 0.63 ng/mL for toxin A and 1.25 ng/ml for toxin B | ≥ 1.4 ng/ml of toxin A & ≥ 2.4 ng/ml of toxin B |
| Clinical sensitivity | 90.2 % (84.1 - 94.2% C.I.) | 94.7% (88.1 – 98.3% C.I.) |
| Clinical specificity | 99.7 % (98.8 – 99.9% C.I.) | 97.3% (95.4 – 98.5% C.I.) |

K. Standard/Guidance Document Referenced (if applicable):
“Review Criteria for Devices assisting in the diagnosis of C. difficile associated disease” May 1990, ODE/CDRH Guidance Document

L. Test Principle:
The device contains a Reaction Window with two vertical lines of immobilized antibodies (Fig. 1a). The test line (“T”) contains antibodies against C. difficile toxins A and B. The control line (“C”) contains anti-IgG antibodies. The Conjugate consists of antibodies to toxins A and B coupled to horseradish peroxidase. To perform the test, the

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fecal specimen is diluted with Diluent and Conjugate is added to the diluted sample. The diluted sample-conjugate mixture is added to the Sample Well and the device is allowed to incubate at room temperature for 15 minutes. During the incubation, any toxin A and toxin B in the sample bind to anti-toxin antibody-peroxidase conjugate. The toxin-antibody complexes migrate through a filter pad to a membrane where they are captured by the immobilized anti-toxin antibodies in the line. The Reaction Window is subsequently washed with Wash Buffer, and the test is developed with the addition of Substrate. After a 10 minute incubation period, the "T" reaction is examined visually for the appearance of a vertical blue line on the "T" side of the Reaction Window. A blue line indicates a positive test. A positive "C" reaction, indicated by a vertical blue line on the "C" side of the Reaction Window, confirms that the test is working properly and the results are valid.

## M. Performance Characteristics (if/when applicable):

### 1. Analytical performance:

#### a. Precision/Reproducibility:

The reproducibility of the TOX A/B QUIK CHEK™ test was determined using known positive (n=6) and negative (n=2) fecal specimens that were coded and masked. Testing was performed at 3 laboratories, which tested the samples on 3 days. The samples produced the expected results 100% of the time.

#### b. Linearity/assay reportable range:

N/A

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

N/A

#### d. Detection limit:

The analytical sensitivity was determined using serial two-fold dilutions of highly purified toxins A and B. Toxins were purified using standard in-house procedures. Six separate tests were conducted for each toxin and the test was consistently positive at a concentration of 0.63 ng/ml for toxin A and 1.25 ng/ml for toxin B.

#### e. Analytical specificity:

CROSS REACTIVITY

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Fecal specimens inoculated with the following microorganisms to a final concentration of approximately $10^{8}$ or higher organisms per mL did not react in the TOX A/B QUIK CHEK™:

**Bacteria**: Aeromonas hydrophila, Bacillus cereus, Bacillus subtilis, Bacteroides fragilis, Campylobacter coli, Campylobacter fetus, Campylobacter jejuni, Candida albicans, Clostridium bifermentans, Clostridium butyricum, Clostridium perfringens, Clostridium septicum, Clostridium sordellii (nontoxigenic), Clostridium sporogenes, Enterococcus faecalis, Escherichia coli EIEC, Escherichia coli, Escherichia coli 0157 H7, Escherichia coli ETEC, Klebsiella pneumoniae, Peptostreptococcus anaerobius, Proteus vulgaris, Pseudomonas aeruginosa, Salmonella typhimurium, Shigella dysenteriae, Shigella flexneri, Shigella sonnei, Staphylococcus aureus, Staphylococcus aureus (Cowans), Staphylococcus epidermidis, Vibrio parahaemolyticus, Yersinia enterocolitica

**Viruses**: Adenovirus types 1,2,3,5,40,41, Human coronavirus, Coxsackievirus B2,B3,B4,B5, Echovirus 9,11,18,22,33, Enterovirus type 68,69,70,71.

The only non-C. difficile organism to react with the TOX A/B QUIK CHEK™ was C. sordellii VPI 9048. This strain produces toxins HT and LT, which are homologous to toxins A and B, respectively.

## INTERFERING SUBSTANCES

The following substances had no effect on test results when present in feces in the concentrations indicated: mucin (3.5% w/v), human blood (40% v/v), barium sulfate (5% w/v), Imodium® (5% w/v), Kaopectate® (5 mg/mL), Pepto-Bismol® (5% w/v), steric/palmitic acid (40% w/v), Metronidazole (0.25% w/v), Vancomycin (0.25% w/v).

f. Assay cut-off:

The assay was determined to detect Toxin A at 0.63 ng/ml and Toxin B at 1.25 ng/ml

2. Comparison studies:

a. Method comparison with predicate device:

N/A

b. Matrix comparison:

N/A

3. Clinical studies:

a. Clinical Sensitivity:

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The TOX A/B QUIK CHEK™ test was compared with the tissue culture test at three U.S. hospitals and in-house at TECHLAB®, Inc. Specimens included in the evaluation were submitted to the clinical laboratory for routine testing. The tissue culture test was done according to the in-house procedure. The table below shows a summary of the clinical performance of the TOX A/B QUIK CHEK™ test. The test exhibited a sensitivity and specificity of 90.2% and 99.7%, respectively. The predictive positive and negative values were 98.6% and 97.9%, respectively, and the correlation was 98.0%.

Table 1. Correlation of the TOX A/B QUIK CHEK™ test with tissue culture.

| N = 842 | Tiss cult pos | Tiss cult neg |
| --- | --- | --- |
| TOX A/B QUIK CHEK™ pos | 138 | 2 |
| TOX A/B QUIK CHEK™ neg | 15 | 687 |
| | | 95% CI |
| --- | --- | --- |
| Sensitivity | 90.2 | 84.1 - 94.2 |
| Specificity | 99.7 | 98.8 - 99.9 |
| Predictive Positive Value | 98.6 | 94.4 - 99.8 |
| Predictive Negative Value | 97.9 | 96.4 - 98.7 |
| Correlation | 98.0 | 97.8 - 98.2 |

Of the 2 tissue culture-negative/TOX A/B QUIK CHEK™-positive samples, one was negative in a commercial toxin A+B ELISA. Of the 15 specimens that were tissue culture-positive/TOX A/B QUIK CHEK™-negative, 12 were negative in commercial toxin A+B ELISAs. There were nine specimens that were unreadable. Those specimens were negative by PCR analysis for the genes of toxin A (tcdA) and toxin B (tcdB).

A total of 51 fecal specimens diluted in Cary Blair and 32 fecal specimens diluted in C&S Transport Media were tested in the TOX A/B QUIK CHEK™ test and the results were compared to those obtained by routine testing. The test exhibited an agreement of 97.6% for the detection of C. difficile toxins in specimens prepared in Transport Media.

b. Clinical specificity:

See Sec. M.3.a.

c. Other clinical supportive data (when a. and b. are not applicable):

N/A

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4. Clinical cut-off:

See limit of detection above Sec. M.1.d

5. Expected values/Reference range:

The reported incidence of *C. difficile*-associated disease in patients with antibiotic-associated diarrhea is 10 to 20%. In the studies conducted with this device, the incidence ranged from 10% to 22%. The prevalence of a positive TOX A/B QUIK CHEK™ test will vary from location to location and hospitals may experience rates lower or higher than those observed at the sites used in this evaluation. Clostridium difficile disease is primarily a nosocomial disease of elderly patients, and hospitals that have higher numbers of elderly patients may experience higher rates. It is important to consider any test results in conjunction with clinical symptoms because some healthy adults and large numbers of healthy infants (up to 50%) will be positive for *C. difficile* toxin.

N. Proposed Labeling:

The labeling is sufficient and it satisfies the requirements of 21 CFR Part 809.10.

O. Conclusion:

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