(584 days)
The Digene HCII GC-ID Test is a nucleic acid hybridization assay with signal amplification using microplate chemiluminescence for the qualitative detection of N. gonorrhoeae DNA in cervical specimens collected using the Digene Cervical Sampler™ (Digene cervical brush and Digene Specimen Transport Medium) and in cervical specimens collected using the Digene Swab Specimen Collection Kit ([Swab SCK] Dacron® swab and Digene Specimen Transport Medium). The Digene HCII GC-ID Test is indicated for use as an aid in diagnosing infection with N. gonorrhoeae in symptomatic or asymptomatic females.
The HCII GC-ID Test may be used alone or as a supplemental test to the Digene HCII CT/GC Test to detect N. gonorrhoeae in specimens that are positive by the HCII CT/GC Test.
The Digene GC-ID Test using Hybrid Capture II technology is a nucleic acid hybridization assay with signal amplification that utilizes microplate chemiluminescent detection. Specimens containing the target DNA hybridize with a specific GC RNA probe cocktail. The resultant RNA:DNA hybrids are captured onto the surface of a microplate well coated with antibodies specific for RNA:DNA hybrids. Immobilized hybrids are then reacted with alkaline phosphatase conjugated antibodies specific for RNA:DNA hybrids, and detected with a chemiluminescent substrate. Several alkaline phosphatase molecules are conjugated to each antibody. Multiple conjugated antibodies bind to each captured hybrid resulting in substantial signal amplification. As the substrate is cleaved by the bound alkaline phosphatase, light is emitted which is measured as relative light units (RLUs) on a luminometer. The intensity of the light emitted denotes the presence or absence of target DNA in the specimen.
An RLU measurement equal to or greater than the Cutoff Value indicates the presence of GC DNA in the specimen. An RLU measurement less than the Cutoff Value indicates the absence of GC DNA or GC DNA levels below the detection limit of the assay.
The GC Probe Cocktail contains a probe mixture specifically chosen to eliminate or minimize cross-reactivity with DNA sequences from human cells, other bacterial species, or Neisseria species other than gonorrhoeae. The GC Probe Cocktail supplied with the Digene GC-JD Test is complementary to approximately 9,700 bp or 0.5% of the Neisseria gonorrhoeae genomic DNA (1.9 x 108 bp) . One probe is complementary to 100% of the cryptic plasmid of 4,200 bp.
The Digene HCII GC-ID Test is a nucleic acid hybridization assay for the qualitative detection of N. gonorrhoeae DNA. The acceptance criteria and the study proving the device meets these criteria are detailed below.
1. Table of Acceptance Criteria and Reported Device Performance
The document does not explicitly state pre-defined acceptance criteria for the clinical performance (sensitivity, specificity, PPV, NPV). However, it presents the calculated performance characteristics, which serve as the "reported device performance." The non-clinical performance (precision and analytical sensitivity) demonstrates compliance with established laboratory testing standards.
Non-Clinical Performance:
| Acceptance Criteria Category | Specific Metric | Target/Range (Implicit) | Reported Device Performance |
|---|---|---|---|
| Precision | Within Instrument Variability (Relative Light Units/Cutoff - RLU/CO %CV) | Low variability %CV, suggesting consistent results within the same instrument. (Although not explicitly stated, typical precision studies aim for low %CV, often below 15-20% for quantitative assays, with potentially higher allowances for very low concentrations near the detection limit.) | %CVs for RLU/CO: |
- Panel 1: 10.68%
- Panel 2: 11.50%
- Panel 3 (low concentration): 4.65%
- Panel 4: 5.41%
- Panel 5: 6.50%
- Panel 6: 5.83%
Qualitative results were 100% (54/54) in agreement with expected results. |
| | Between Instrument Variability (RLU/CO %CV) | Low variability %CV when using different instruments. | %CVs for RLU/CO: - Panel 1: 1.73%
- Panel 2: 1.56%
- Panel 3 (low concentration): 1.10%
- Panel 4: 1.37%
- Panel 5: 0.69%
- Panel 6: 1.91% |
| | Within Run Variability (RLU/CO %CV) | Low variability %CV for tests run in the same batch. | %CVs for RLU/CO: - Panel 1: 28.26%
- Panel 2: 34.94%
- Panel 3 (low concentration): 10.89%
- Panel 4: 8.85%
- Panel 5: 13.48%
- Panel 6: 13.12% |
| | Total Precision (RLU/CO %CV) | Overall low variability %CV over repeated tests under various conditions. | %CVs for RLU/CO: - Panel 1: 28.20%
- Panel 2: 35.42%
- Panel 3 (low concentration): 11.96%
- Panel 4: 9.08%
- Panel 5: 13.26%
- Panel 6: 12.90% |
| Analytical Sensitivity | Limit of Detection (LOD) (CFU/assay) | Ability to detect N. gonorrhoeae at low concentrations across a range of isolates, auxotypes, and strains. (No specific numerical target is stated, but the aim is to establish the LOD for the test.) | Varied from 25 to 50,000 CFU/assay for 114 N. gonorrhoeae isolates.
Average detectable limit: 974 to 2887 CFU/assay.
Overall average LOD: 1931 CFU/assay (3.8 x 104 CFU/ml). |
Clinical Performance (Brush Specimens - All Patients Combined, using 1.0 RLU/CO cutoff):
| Acceptance Criteria Category | Specific Metric | Target/Range (Implicit) | Reported Device Performance (All Sites Combined, 1.0 cutoff) | 95% Confidence Interval (All Sites Combined, 1.0 cutoff) |
|---|---|---|---|---|
| Clinical Performance | Sensitivity | Demonstrates effective detection of N. gonorrhoeae compared to culture. (No specific numerical threshold is given, but typically clinical diagnostic tests aim for high sensitivity). | 92.55% | 85.3-97.0% |
| Specificity | Demonstrates accurate identification of true negatives compared to culture. (Typically, clinical diagnostic tests aim for high specificity). | 98.50% | 98.6-99.6% | |
| PPV | High probability that a positive test result correctly indicates infection. | 82.08% | 81.3-94.8% | |
| NPV | High probability that a negative test result correctly indicates no infection. | 99.44% | 98.9-99.8% |
Note: The document provides results for both 1.0 and 2.5 RLU/CO cutoffs. The table above uses the 1.0 RLU/CO cutoff as it generally represents higher sensitivity, and the primary table uses this as the first reported value. Differences for the 2.5 cutoff are parenthetically provided in the original text.
2. Sample Sizes and Data Provenance
- Test Set Sample Size (Clinical Study): 1825 clinical specimens.
- Brush specimens: 1359 (Table 3)
- Swab specimens: 466 (Table 4)
- Data Provenance: Prospective. Specimens were collected from patients at 5 different clinical sites (STD, Family Planning, and OB/GYN clinics) for the multi-center clinical trial. Countries of origin are not specified but implied to be within the US given the FDA submission.
3. Number of Experts and Qualifications for Ground Truth
- The ground truth for the clinical study was primarily established using Gonorrhea culture. This is a laboratory-based method, not typically requiring "experts" in the sense of physicians or radiologists making subjective calls, but rather trained microbiologists performing and interpreting the cultures.
- For specimens that were Digene GC-ID Test-positive/culture-negative, PCR testing was performed. This also relies on laboratory expertise. The document states that "Digene GC-ID Test results were NOT resolved by PCR test results and therefore PCR had no impact on the calculations of the Digene GC-ID Test performance characteristics." This implies PCR was used for further investigation but not to alter the primary ground truth against which sensitivity/specificity were calculated.
4. Adjudication Method for the Test Set
The primary ground truth for the clinical study was Gonorrhea culture. For discordant results (GC-ID positive/Culture negative), PCR testing was performed for additional information, but the document explicitly states that the Digene GC-ID Test results were not resolved by PCR test results for the calculation of performance characteristics. Therefore, there was no expert adjudication process to determine a "final" ground truth from multiple conflicting results; culture was the single arbiter for the main performance calculations.
In the section "Retesting of HCII CT/GC Test Positive Specimens using the GC-ID Test," combined GC Culture and PCR was used as a reference standard, and an equivocal zone was defined for the GC-ID test, where specimens falling in this zone could be retested.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study
No, an MRMC comparative effectiveness study involving human readers with and without AI assistance was not mentioned or conducted. This device is an in vitro diagnostic test that directly detects nucleic acids, not an imaging device requiring human interpretation, so human reader studies are not applicable.
6. Standalone (Algorithm Only) Performance
Yes, the study primarily evaluated the standalone performance of the Digene HCII GC-ID Test. The reported sensitivity, specificity, PPV, and NPV are measures of the algorithm's (test's) performance independent of human interpretation or assistance, against a gold standard (culture).
7. Type of Ground Truth Used
- Clinical Study: The primary ground truth for the clinical performance evaluation was Gonorrhea culture.
- Discordant Resolution (for investigational purposes, not main metrics): PCR testing was used to further investigate Digene GC-ID Test-positive/culture-negative specimens.
- Retesting HCII CT/GC Positive Specimens: Combined GC Culture and PCR.
8. Sample Size for the Training Set
The document does not explicitly mention a "training set" for the Digene HCII GC-ID Test in the context of an algorithm or machine learning model. This device is a biochemical assay, not a software algorithm that undergoes machine learning training. The data presented is for validation and performance characteristics.
9. How the Ground Truth for the Training Set Was Established
As noted above, there is no mention of a "training set" in the machine learning sense. The device's design and probe cocktail selection (complementary to N. gonorrhoeae genomic DNA, minimizing cross-reactivity) would be based on scientific knowledge and laboratory development, not iterative training on a labeled dataset.
§ 866.3390
Neisseria spp. direct serological test reagents.(a)
Identification. Neisseria spp. direct serological test reagents are devices that consist of antigens and antisera used in serological tests to identifyNeisseria spp. from cultured isolates. Additionally, some of these reagents consist ofNeisseria spp. antisera conjugated with a fluorescent dye (immunofluorescent reagents) which may be used to detect the presence ofNeisseria spp. directly from clinical specimens. The identification aids in the diagnosis of disease caused by bacteria belonging to the genusNeisseria, such as epidemic cerebrospinal meningitis, meningococcal disease, and gonorrhea, and also provides epidemiological information on diseases caused by these microorganisms. The device does not include products for the detection of gonorrhea in humans by indirect methods, such as detection of antibodies or of oxidase produced by gonococcal organisms.(b)
Classification. Class II (performance standards).