(498 days)
The Light Diagnostics Rabies DFA Reagent is intended for the detection of rabies antigens in culture and in acetone-fixed brain and submaxillary tissues of infected animals. Thus the assay could be used as an aid in the indirect diagnosis of human rabies virus infection. All specimens that are negative or indeterminate by DFA testing should be further tested by cell culture or animal inoculation methods.
Light Diagnostics Rabies DFA Reagent uses fluorescein-labeled monoclonal antibodies directed against the rabies nucleocapsid protein to detect the virus in infected tissue. The direct immunofluorescence assay requires incubation of a user-determined dilution of the reagent with suspected rabies-infected tissue such as brain (medulla, cerebellum, and hippocampus) and submaxillary salivary glands. If virus is present, the FITC-labeled monoclonal antibodies will bind to the nucleocapsid protein. Unbound antibody is removed by washing. The antigen-antibody complex is visualized using fluorescence microscopy. Positive reactions in infected tissue will appear as bright apple-green cytoplasmic inclusions or "dusting". A blend of monoclonal antibodies are used in the Light Diagnostics Rabies DFA reagent. These monoclonal antibodies are specific for the rabies virus nucleocapsid protein. The use of monoclonal antibodies ensures increased specificity of the reagent and reduces the risk of non-specific background or interference.
Here's an analysis of the provided text, extracting the requested information about acceptance criteria and the study proving device performance:
Acceptance Criteria and Device Performance Study
1. Table of Acceptance Criteria and Reported Device Performance
The provided document defines "substantial equivalence" to predicate devices as the primary acceptance criterion. While no explicit numerical targets for sensitivity and specificity are stated as acceptance criteria, the study's results demonstrate 100% agreement, implying that the acceptance criterion was likely at least matching the performance of the predicate devices.
| Metric | Acceptance Criteria (Implied) | Reported Device Performance (Site 1) | Reported Device Performance (Site 2) |
|---|---|---|---|
| Relative Sensitivity | Substantially equivalent to predicate devices (BBL and Centocor) | 100% (95% CI: 0.903 to 1.001) | 100% (95% CI: 0.925 to 1.001) |
| Relative Specificity | Substantially equivalent to predicate devices (BBL and Centocor) | 100% (95% CI: 0.991 to 1.001) | 100% (95% CI: 0.996 to 1.001) |
2. Sample Size Used for the Test Set and Data Provenance
- Test Set Sample Size:
- Site 1: 454 specimens
- Site 2: 1036 specimens
- Total: 1490 specimens
- Data Provenance: The studies were performed at two sites in the United States: "Site 1 was on the west coast and Site 2 was in the south central part of the country." The data is retrospective, as it involves testing previously collected "specimens from 23 animal species" and "specimens from 25 animal species."
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Qualifications of Those Experts
The document does not explicitly state the number or qualifications of experts used to establish the ground truth. Instead, the "ground truth" for the clinical evaluation was established by two predicate devices: BECTON DICKINSON BBL® Anti-Rabies Globulin, Fluorescein Labeled and Centocor FITC Anti-Rabies Monoclonal Globulin.
4. Adjudication Method for the Test Set
The document implies a direct comparison without explicit adjudication: "Complete agreement was seen between the commercially available in vitro diagnostic reagents and the Working Dilution of the FITC-conjugate monoclonal reagent." It directly compares the test device's results to the predicate devices' results. There is no mention of a formal adjudication process involving multiple human readers to resolve discrepancies.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done, and the Effect Size of How Much Human Readers Improve with AI vs Without AI Assistance
No, a multi-reader, multi-case (MRMC) comparative effectiveness study was not done. This study is a standalone performance evaluation of a diagnostic reagent (antibody) compared to existing predicate reagents, not an assessment of human reader performance with or without AI assistance. The document predates widespread AI in medical diagnostics (1998).
6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done
Yes, a standalone study was done. The "Light Diagnostics Rabies DFA Reagent" is a diagnostic reagent, and its performance was evaluated inherently in a "standalone" manner by directly comparing its reactive properties (antigen detection) to the predicate reagents on biological specimens. The "human-in-the-loop" aspect here refers to the laboratory technicians performing the DFA assay and reading the fluorescence microscope, but the device under evaluation itself is the reagent, not an automated algorithm or AI.
7. The Type of Ground Truth Used
The ground truth used for the clinical evaluation was based on the consensus/results of predicate diagnostic devices (BECTON DICKINSON BBL® Anti-Rabies Globulin, Fluorescein Labeled and Centocor FITC Anti-Rabies Monoclonal Globulin). In one instance at Site 1, "Laboratory inoculation of mice with samples from other animals resulted in a positivity rate of 66.7%," suggesting that in some cases, animal inoculation (a biological outcome/referral standard) was also used as a reference for some specimens, especially if the predicate devices were not conclusive or to establish the true positivity rate of samples before the predicate comparison. However, the performance metrics reported are relative to the predicate devices.
8. The Sample Size for the Training Set
No explicit "training set" is mentioned in the context of machine learning. However, the monoclonal antibodies themselves were "trained" or rather developed and characterized using a panel of "twenty (20) variants of rabies virus," including various species and geographic strains. This characterization step serves a similar purpose to a training or development phase for the reagent's specificity.
9. How the Ground Truth for the Training Set Was Established
For the "training set" (characterization of the monoclonal antibodies): The ground truth was established by testing the conjugated monoclonal antibodies against "twenty (20) variants of rabies virus." These variants were "differentiated using panels of monoclonal antibodies, and represent all of the epidemiologically significant street rabies variants." This implies that the identity of these rabies virus variants was already established through prior scientific methods (e.g., genetic sequencing, established serotyping using reference panels). The "strong affinity" of the test reagent to these known variants confirmed its broad reactivity.
§ 866.3460 Rabiesvirus immunofluorescent reagents.
(a)
Identification. Rabiesvirus immunofluorescent reagents are devices that consist of rabiesvirus antisera conjugated with a fluorescent dye used to identify rabiesvirus in specimens taken from suspected rabid animals. The identification aids in the diagnosis of rabies in patients exposed by animal bites and provides epidemiological information on rabies. Rabies is an acute infectious disease of the central nervous system which, if undiagnosed, may be fatal. The disease is commonly transmitted to humans by a bite from a rabid animal.(b)
Classification. Class II (performance standards).