(150 days)
TRU FLU is a rapid, qualitative, lateral-flow immunochromatographic assay for detecting both influenza A and influenza B viral nucleoprotein antigens in human nasal wash, nasopharyngeal aspirate and nasal and nasopharyngeal swab samples from symptomatic patients. The test is not intended for the detection of influenza C viruses A negative test is presumptive and it is recommended these results be confirmed by cell culture. Negative results do not preclude influenza virus infection and should not be used as the sole basis for treatment or other clinical management decisions.
TRU FLU is a single use immunoassay that consists of a Conjugate Tube, a Test Strip, and Sample Diluent. The Conjugate Tube contains a lyophilized bead of colloidal gold-linked monoclonal antibodies to influenza A and influenza B (detector antibodies). The Test Strip carries a nitrocellulose membrane with dried capture antibodies at separate lines for influenza B. The Test Strip holder caps the Conjugate Tube during testing and subsequent disposal to reduce exposure to potential pathogens.
The conjugate bead is first rehydrated in the Conjugate Tube with Sample Diluent, prior to the addition of patient specimen. The contents are mixed before the Test Strip is added. As the test is incubated at 20-25 C. influenza A or influenza B antigens, if present in the diluted sample, bind to the corresponding monoclonal antibody-colloidal gold conjugate as the sample moves up the Test Strip. The influenza A capture monoclonal antibody is bound to the Test Strip at the test-FLU A position of the device. When it binds the antigen-influenza A antibody-colloidal gold complex, it yields a visible pink-red line. Similarly, the influenza B capture monoclonal antibody bound to the assay membrane at the test-FLU B position will result in a pink-red line when it captures antibody-colloidal gold complexes. When no antigen is present, no complexes are formed and no pink-red line will appear at either the test FLU A or the test FLU B position of the Test Strip. An internal control line helps determine whether adequate flow has occurred through the Test Strip during a test run. A visible pink-red line at the Control position of the Test Strip should be present each time a specimen or control is tested. If no pink-red control line is seen, the test is considered invalid.
Here's a summary of the acceptance criteria and the study proving the device meets them, based on the provided text:
Device: TRU FLU (Rapid, qualitative lateral-flow immunoassay for the detection of Influenza A and B antigens)
Indications for Use: Rapid, qualitative, lateral-flow immunochromatographic assay for detecting both influenza A and influenza B viral nucleoprotein antigens in human nasal wash, nasopharyngeal aspirate and nasal and nasopharyngeal swab samples from symptomatic patients. Not intended for detection of influenza C viruses. Negative results are presumptive and should be confirmed by cell culture; they should not be the sole basis for treatment or clinical management.
1. Table of Acceptance Criteria and Reported Device Performance
The document does not explicitly state pre-defined acceptance criteria (e.g., "Sensitivity must be >= 90%"). However, based on the performance evaluation and the 510(k) clearance, the implied acceptance criteria are that the device demonstrates substantial equivalence to the reference method (tissue culture) and the predicate device (Binax NOW Influenza A&B) in terms of sensitivity and specificity for both Influenza A and B across different sample types and patient demographics.
Here's the summarized reported device performance against the "Gold Standard" (Tissue Culture):
| Metric | Subgroup | TRU FLU Influenza A Performance (vs. Tissue Culture) | TRU FLU Influenza B Performance (vs. Tissue Culture) |
|---|---|---|---|
| Overall Sensitivity | Fresh Wash/Aspirate | 87.2% (95% CI: 72.6 - 95.7%) | 63.6% (95% CI: 45.1 - 79.6%) |
| Fresh Swab | 86.3% (95% CI: 76.3 - 93.2%) | 58.5% (95% CI: 45.6 - 70.6%) | |
| Frozen Wash/Aspirate | 85.0% (95% CI: 62.1 - 96.8%) | 50.0% (95% CI: 1.3 - 98.7%) | |
| Overall Specificity | Fresh Wash/Aspirate | 89.3% (95% CI: 85.9 - 92.6%) | 99.4% (95% CI: 97.8 - 99.9%) |
| Fresh Swab | 92.7% (95% CI: 88.7 - 95.6%) | 99.6% (95% CI: 97.8 - 100%) | |
| Frozen Wash/Aspirate | 93.0% (95% CI: 80.9 - 98.5%) | 100.0% (95% CI: 94.1 - 100%) | |
| Reproducibility | High Positive & Low Negative | 100% correct results | 100% correct results |
| High Negative (near LOD) | Weakly positive results in 8/72 replicates | N/A (not specified as often for B) | |
| Low Positive (just above LOD) | 1 negative reaction out of 72 replicates | N/A (not specified as often for B) |
(Note: "N/A" in the table above for 95% CI when only 1 positive sample existed implies the CI was not calculable or meaningful for such a small n, which is a limitation of some individual site data, not the overall study.)
2. Sample Size and Data Provenance
- Test Set Sample Size:
- Total Samples: 697 prospectively collected fresh samples + 63 frozen samples = 760 samples (after excluding 1 invalid tissue culture result from the 697 prospective samples for sensitivity/specificity calculations).
- Fresh Samples: 697 samples (366 wash/aspirate, 320 swab, 11 not defined).
- Frozen Samples: 63 samples (all wash/aspirate).
- Data Provenance:
- Country of Origin: United States. The study states "Nine independent laboratories (in different geographic regions of the US) and the manufacturer participated in the study."
- Retrospective or Prospective: Primarily prospective. "The test plan was designed to evaluate the performance of prospectively collected fresh and frozen samples from the 2006-7 season." The document also mentions "prospectively collected fresh and 63 frozen samples were tested." Tissue culture on frozen samples was performed at the time of collection.
3. Number of Experts and Qualifications for Ground Truth
- Number of Experts: Not specified. The ground truth (tissue culture) was performed at "each laboratory's established internal method." It does not explicitly state that experts established a consensus ground truth for the device evaluation; rather, a standard laboratory method was employed.
- Qualifications of Experts: Not specified. It's assumed that standard certified laboratory personnel performed the tissue culture, but specific qualifications (e.g., "clinical microbiologist with X years of experience") are not detailed.
4. Adjudication Method for the Test Set
The document does not describe any specific adjudication method (like 2+1 or 3+1) for resolving discrepancies between the TRU FLU results and the tissue culture results. The tissue culture results appear to have been used directly as the reference standard without further expert adjudication mentioned.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
No, a Multi-Reader Multi-Case (MRMC) comparative effectiveness study was not done. This study focuses on the standalone performance of the TRU FLU device against a gold standard (tissue culture) and compares it to a predicate device, not on assessing human reader improvement with or without AI assistance. The device in question is a rapid diagnostic test, not an AI-assisted diagnostic tool.
6. Standalone Performance Study
Yes, a standalone study was performed. The entire clinical performance evaluation section describes the algorithm's (TRU FLU device's) performance without human intervention, specifically comparing its results against the tissue culture gold standard. The device requires no instruments and is read directly by a user. The sensitivity and specificity values reported are representative of the device's standalone performance.
7. Type of Ground Truth Used
The type of ground truth used was tissue culture isolation. The document explicitly states: "Tissue culture isolation remains the gold standard for the detection of influenza, yet the procedure can take 7 days to complete". It further confirms: "Trial sites were instructed to test samples in parallel by tissue culture (standard reference), TRU FLU and the predicate device, NOW Influenza A&B. Tissue culture (reference method) was performed by the site using the site's method."
8. Sample Size for the Training Set
The document does not provide information regarding a separate "training set" or its sample size. This is common for traditional in-vitro diagnostic devices (like lateral-flow immunoassays) where the "training" analogous to machine learning models is typically the biochemical assay design and optimization, followed by verification and validation, rather than a distinct data-driven training phase on labeled data. The study described focuses on clinical validation of the final device.
9. How Ground Truth for the Training Set Was Established
As no separate "training set" is mentioned (see point 8), the document does not describe how ground truth for such a set was established. The clinical evaluation sets (fresh and frozen samples) used tissue culture as the ground truth, as detailed in point 7.
§ 866.3328 Influenza virus antigen detection test system.
(a)
Identification. An influenza virus antigen detection test system is a device intended for the qualitative detection of influenza viral antigens directly from clinical specimens in patients with signs and symptoms of respiratory infection. The test aids in the diagnosis of influenza infection and provides epidemiological information on influenza. Due to the propensity of the virus to mutate, new strains emerge over time which may potentially affect the performance of these devices. Because influenza is highly contagious and may lead to an acute respiratory tract infection causing severe illness and even death, the accuracy of these devices has serious public health implications.(b)
Classification. Class II (special controls). The special controls for this device are:(1) The device's sensitivity and specificity performance characteristics or positive percent agreement and negative percent agreement, for each specimen type claimed in the intended use of the device, must meet one of the following two minimum clinical performance criteria:
(i) For devices evaluated as compared to an FDA-cleared nucleic acid based-test or other currently appropriate and FDA accepted comparator method other than correctly performed viral culture method:
(A) The positive percent agreement estimate for the device when testing for influenza A and influenza B must be at the point estimate of at least 80 percent with a lower bound of the 95 percent confidence interval that is greater than or equal to 70 percent.
(B) The negative percent agreement estimate for the device when testing for influenza A and influenza B must be at the point estimate of at least 95 percent with a lower bound of the 95 percent confidence interval that is greater than or equal to 90 percent.
(ii) For devices evaluated as compared to correctly performed viral culture method as the comparator method:
(A) The sensitivity estimate for the device when testing for influenza A must be at the point estimate of at least 90 percent with a lower bound of the 95 percent confidence interval that is greater than or equal to 80 percent. The sensitivity estimate for the device when testing for influenza B must be at the point estimate of at least 80 percent with a lower bound of the 95 percent confidence interval that is greater than or equal to 70 percent.
(B) The specificity estimate for the device when testing for influenza A and influenza B must be at the point estimate of at least 95 percent with a lower bound of the 95 percent confidence interval that is greater than or equal to 90 percent.
(2) When performing testing to demonstrate the device meets the requirements in paragraph (b)(1) of this section, a currently appropriate and FDA accepted comparator method must be used to establish assay performance in clinical studies.
(3) Annual analytical reactivity testing of the device must be performed with contemporary influenza strains. This annual analytical reactivity testing must meet the following criteria:
(i) The appropriate strains to be tested will be identified by FDA in consultation with the Centers for Disease Control and Prevention (CDC) and sourced from CDC or an FDA-designated source. If the annual strains are not available from CDC, FDA will identify an alternative source for obtaining the requisite strains.
(ii) The testing must be conducted according to a standardized protocol considered and determined by FDA to be acceptable and appropriate.
(iii) By July 31 of each calendar year, the results of the last 3 years of annual analytical reactivity testing must be included as part of the device's labeling. If a device has not been on the market long enough for 3 years of annual analytical reactivity testing to have been conducted since the device received marketing authorization from FDA, then the results of every annual analytical reactivity testing since the device received marketing authorization from FDA must be included. The results must be presented as part of the device's labeling in a tabular format, which includes the detailed information for each virus tested as described in the certificate of authentication, either by:
(A) Placing the results directly in the device's § 809.10(b) of this chapter compliant labeling that physically accompanies the device in a separate section of the labeling where the analytical reactivity testing data can be found; or
(B) In the device's label or in other labeling that physically accompanies the device, prominently providing a hyperlink to the manufacturer's public Web site where the analytical reactivity testing data can be found. The manufacturer's home page, as well as the primary part of the manufacturer's Web site that discusses the device, must provide a prominently placed hyperlink to the Web page containing this information and must allow unrestricted viewing access.
(4) If one of the actions listed at section 564(b)(1)(A)-(D) of the Federal Food, Drug, and Cosmetic Act occurs with respect to an influenza viral strain, or if the Secretary of Health and Human Services (HHS) determines, under section 319(a) of the Public Health Service Act, that a disease or disorder presents a public health emergency, or that a public health emergency otherwise exists, with respect to an influenza viral strain:
(i) Within 30 days from the date that FDA notifies manufacturers that characterized viral samples are available for test evaluation, the manufacturer must have testing performed on the device with those viral samples in accordance with a standardized protocol considered and determined by FDA to be acceptable and appropriate. The procedure and location of testing may depend on the nature of the emerging virus.
(ii) Within 60 days from the date that FDA notifies manufacturers that characterized viral samples are available for test evaluation and continuing until 3 years from that date, the results of the influenza emergency analytical reactivity testing, including the detailed information for the virus tested as described in the certificate of authentication, must be included as part of the device's labeling in a tabular format, either by:
(A) Placing the results directly in the device's § 809.10(b) of this chapter compliant labeling that physically accompanies the device in a separate section of the labeling where analytical reactivity testing data can be found, but separate from the annual analytical reactivity testing results; or
(B) In a section of the device's label or in other labeling that physically accompanies the device, prominently providing a hyperlink to the manufacturer's public Web site where the analytical reactivity testing data can be found. The manufacturer's home page, as well as the primary part of the manufacturer's Web site that discusses the device, must provide a prominently placed hyperlink to the Web page containing this information and must allow unrestricted viewing access.