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The Abbott RealTime CT/NG (List No. 8L07-91) assay is an in vitro polymerase chain reaction (PCR) assay for the direct, qualitative detection of the plasmid DNA of Chlamydia trachomatis and the genomic DNA of Neisseria gonorrhoeae. The assay may be used to test the following specimens from symptomatic individuals: female endocervical swab, clinician-collected vaginal swab, and patient-collected vaginal swab specimens; male urethral swab specimens; and female and male urine specimens. The assay may be used to test the following specimens from asymptomatic individuals: clinician-collected vaginal swab and patient-collected vaginal swab specimens; female and male urine specimens.

Abbott RealTime CT/NG consists of two reagent kits:

• · Abbott RealTime CT/NG Amplification Reagent Kit (List No. 8L07-91)
• · Abbott RealTime CT/NG Control Kit (List No. 8L07-80)
  The Abbott RealTime CT/NG assay uses PCR technology with homogenous real-time fluorescence detection on the m2000 System. The Abbott m2000 System consists of the Abbott m2000sp and Abbott m2000rt instruments. The Abbott m2000 System integrates sample preparation with nucleic acid amplification and detection to generate assay results. The Abbott m2000sp is used for processing samples and the Abbott m2000rt is used for amplification and detection.

Abbott RealTime CT/NG Assay: Acceptance Criteria and Supporting Study

1. Table of Acceptance Criteria and Reported Device Performance

The acceptance criteria for the Abbott RealTime CT/NG assay are implied by the reported clinical sensitivity and specificity for various specimen types and Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) detection. While explicit numerical acceptance criteria are not stated in the provided text, the reported performance values demonstrate the device's efficacy.

Table 1: Clinical Performance of Abbott RealTime CT/NG Assay

2. Sample Size and Data Provenance (Clinical Study)

• Sample Size for Test Set: A total of 3,832 male and female subjects were enrolled in the multi-center clinical study. For the analysis of the Abbott RealTime CT/NG assay, 6,555 CT results and 6,569 NG results were used.
• Data Provenance: The study was conducted in the United States across 16 geographically diverse sites, including physician private practices, public and private STD clinics, and a hospital emergency room. The study design implies a prospective collection of specimens from enrolled subjects, although it's not explicitly stated as retrospective or prospective in every detail of the summary. The phrase "Specimens were collected from subjects at...sites" supports a prospective approach for the clinical data.

3. Number of Experts and Qualifications (Ground Truth)

The document does not explicitly state the "number of experts" or their specific "qualifications" used to establish the ground truth in the clinical study. Instead, the ground truth was established by comparing the Abbott RealTime CT/NG assay to reference assays.

4. Adjudication Method (Test Set)

The adjudication method for determining the "patient infected status" (ground truth) was based on a combination of reference assay results:

• For CT or NG (Female Subjects): A female was categorized as infected if a minimum of two positive results were reported (at least one from each reference NAAT). A specific condition was also applied for CT: if reference urine specimens were positive and all three reference swab specimens were negative, the subject was considered infected for urine but not swab specimens.
• For CT or NG (Male Subjects): A male was categorized as infected if a minimum of two positive results were reported.
• For NG (All Subjects): If the reference NG culture assay result was positive, the subject was categorized as infected regardless of NAAT results.
• Non-Infected Status: For females, non-infected status was assigned if at least one reference NAAT reported negative results for all sample types AND the NG culture was negative. For males, at least two negative results from reference NAATs AND a negative NG culture result were required for non-infected status.
• Subjects with missing and/or indeterminate results from reference assays were excluded from the analysis (4 subjects for CT and 7 subjects for NG).

This multi-assay, rule-based approach serves as the adjudication method for establishing the ground truth.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

No Multi-Reader Multi-Case (MRMC) comparative effectiveness study was mentioned in the provided document. The study is focused on the standalone performance of the Abbott RealTime CT/NG assay against established reference methods, not on comparing human reader performance with and without AI assistance.

6. Standalone Performance (Algorithm Only)

Yes, a standalone performance study was done. The entire clinical study described, measuring the sensitivity and specificity of the Abbott RealTime CT/NG assay against reference methods, represents the standalone performance of the algorithm. The results are summarized in Table 1 above, as well as Tables 3.10-3.13 in the original document.

7. Type of Ground Truth Used

The ground truth used for the clinical study was established by expert consensus using a combination of reference assays:

• Two commercially available Nucleic Acid Amplification Tests (NAATs) for CT and NG.
• Culture for NG.

This is a composite reference standard or adjudicated clinical truth based on multiple established diagnostic methods.

8. Sample Size for the Training Set

The document does not explicitly mention a "training set" or "training data" in the context of the Abbott RealTime CT/NG assay development or validation. This is expected given that the device is an in-vitro diagnostic (IVD) PCR assay, which typically relies on analytical validation and clinical performance studies described here, rather than machine learning models that require distinct training and test sets. The presented clinical study serves as the primary validation of the device's performance.

9. How the Ground Truth for the Training Set Was Established

As noted above, the document does not refer to a distinct "training set." The Limit of Detection (LOD) and analytical sensitivity studies (Sections 3.14.1), which involve testing known concentrations of CT and NG target DNA and isolates, can be considered part of the analytical validation that informs the assay's performance characteristics. For these analytical studies:

• Known concentrations of CT and NG target DNA were used.
• Dilutions of various CT serovars and NG isolates were tested.

This is a form of defined analytical ground truth based on controlled laboratory preparations of the target organisms. For the clinical performance, the ground truth was established by the composite reference standard from the clinical study as detailed in point 7.

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The Digene HCII CT-ID Test is an in-vitro nucleic acid hybridization assay with signal amplification using microplate chemiluminescence for the qualitative detection of C trachomatis DNA in cervical specimens collected using the Digene Cervical Sampler™ (Cervical Brush and Speciment Transport Medium) and in cervical specimens collected using the Digene Swab Specimen Collection Kit (Dacron Swab and Speciment Transport Medium). The Digene HCII CT-ID Test is indicated for use with symptomatic or asymptomatic women as evidence of infection with C. trachomatis.

The HCII CT-ID Test may be used alone or as a supplemental test to the Digene HCII CT/GC Test to detect C. trachomatis DNA in specimens found positive by the Digene HCII CT/GC Test.

The Digene HCII CT-ID Test is a nucleic acid, signal enhanced, hybridization, microplate assay using chemiluminescence for the qualitative detection of C. trachomatis (CT) DNA in cervical specimens collected using the Digene Cervical Sampler™ and in cervical specimens collected with a Dacron swab and placed in Digene Specimen Transport Medium. The Digene HCII CT-ID Test is indicated for use as an aid in diagnosing infection with C. trachomatis in symptomatic or asymptomatic women. The HCII CT-ID Test may be used as a stand-alone test or may be used as a supplemental test to the Digene HCII CT/GC Test for identification of C. trachomatis in specimens that are positive by the HCII CT/GC Test.

Specimens potentially containing CT DNA are denatured and then hybridized with a specific RNA probe cocktail. This cocktail contains a probe mixture chosen to minimize or eliminate cross-reactivity with DNA sequences from human cells, other bacterial species, Chlamydia species other than trachomatis, or sequences from other organisms common in urogenital specimens. The CT probe cocktail supplied with the Digene CT-ID Assay is complementary to approximately 39,300 base pairs or 4% of the C. trachomatis genome (1 x 10 base pairs) and 100% of the cryptic plasmid.

The RNA:DNA hybrids resulting from hybridization are immobilized (captured) on the surface of a microplate-well, which has been coated with antibodies specific for RNA:DNA hybrids. The antibodies on the well surface capture the RNA:DNA hybrids. The immobilized hybrids are then reacted with alkaline phosphatase-conjugated antibody and a chemiluminescent substrate. As the substrate is cleaved by the bound alkaline phosphatase, photons are emitted and measured as Relative Light Units (RLUs) using a standard, FDA-cleared luminometer such as the DML 2000™ - Increased photon emission, resulting in an enhanced signal, is achieved by conjugating multiple alkaline phosphatase molecules to each antibody molecule. Multiple antibodies bind to each RNA:DNA hybrid, further enhancing the signal.

The HCII CT-ID Test provides an RLU measurement that is qualitatively interpreted. The Positive Cutoff Value is equal to the mean of three Positive Control values. Each specimen RLU measurement is converted to a ratio of the Positive Cutoff Value. This conversion calculation is performed automatically by the Digene DML™ 2000 Microplate Luminometer software. Alternatively, the conversion may be calculated manually, Specimens with RLU/Cutoff values of 5.0 are considered positive for CT DNA. Specimens with RLU/Cutoff values between 0.8 ≥ 5.0 are considered to be equivocal and are repeat tested in duplicate. With the repeat tests, a RLU/Cutoff Value of 1.0 is applied. If two of the three replicates fall above 1.0, the presence of C. trachomatis DNA is indicated. If at least two of the three replicates fall below 1.0, the presence of C. trachomatis DNA is not indicated.

Here's an analysis of the acceptance criteria and study findings for the Digene HCII CT-ID Test, based on the provided text:

The document combines a 510(k) summary with results from a clinical study comparing the Digene HCII CT-ID Test to a "gold standard" (cell culture with DFA confirmation).

1. Table of Acceptance Criteria and Reported Device Performance

The document does not explicitly state pre-defined acceptance criteria for sensitivity, specificity, NPV, or PPV. However, it presents the results of a multicenter study comparing the Digene HCII CT-ID Test against the gold standard (Cell Culture/DFA). We can infer the expected performance levels from the 'All' sites aggregated results.

Inferred Acceptance Criteria and Device Performance (Aggregated "All" Sites):

| Performance Metric | Implied Acceptance Criteria (e.g., from Predicate or clinical utility) | Reported Device Performance (All Sites Combined) |
| :----------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Sensitivity | High sensitivity is crucial for infectious disease diagnostics to minimize false negatives. The predicate device (Gen-Probe Pace 2 System) would have established a benchmark. | 97.25% (95% CI: 92.2-99.4) for "HCII CT-ID Test versus CT Culture/DF/" cohort
100.00% (95% CI: 84.6-100) for "CT/GC Positive/Culture Negative" cohort
84.00% (95% CI: 63.9-95.5) for "Mixed Symptomatic/Asymptomatic" cohort
100.00% (95% CI: 29.2-100) for "Asymptomatic Patients, Dacron Swab Only" cohort |
| Specificity | High specificity is important to minimize false positives and unnecessary treatments. The predicate device would have established a benchmark. | 98.07% (95% CI: 96.9-98.9) for "HCII CT-ID Test versus CT Culture/DF/" cohort
98.29% (95% CI: 96.5-99.3) for "CT/GC Positive/Culture Negative" cohort
97.88% (95% CI: 95.1-99.3) for "Mixed Symptomatic/Asymptomatic" cohort
99.47% (95% CI: 97.1-100) for "Asymptomatic Patients, Dacron Swab Only" cohort |
| NPV (Negative Predictive Value) | High NPV is critical to confidently rule out infection. | 99.63% (95% CI: 98.9-99.9) for "HCII CT-ID Test versus CT Culture/DF/" cohort
100% (95% CI: 99.1-100) for "CT/GC Positive/Culture Negative" cohort
98.30% (95% CI: 95.7-99.5) for "Mixed Symptomatic/Asymptomatic" cohort
100.00% (95% CI: 98.0-100) for "Asymptomatic Patients, Dacron Swab Only" cohort |
| PPV (Positive Predictive Value) | High PPV indicates that a positive result is likely a true positive. | 86.89% (95% CI: 79.6-92.3) for "HCII CT-ID Test versus CT Culture/DF/" cohort
75.86% (95% CI: 56.5-89.7) for "CT/GC Positive/Culture Negative" cohort
80.77% (95% CI: 60.7-93.5) for "Mixed Symptomatic/Asymptomatic" cohort
75.00% (95% CI: 19.4-99.4) for "Asymptomatic Patients, Dacron Swab Only" cohort |

The statement, "A multicenter study has demonstrated that the Digene HCII CT-ID Test performs as well or better than the gold standard, cell culture, in detecting infection with C. trachomatis in the intended population," suggests that the reported performance meets or exceeds the expected standards for a diagnostic device for C. trachomatis.

2. Sample Size Used for the Test Set and Data Provenance

• Sample Size for the Test Set:

  • Total (HCII CT-ID Test vs. CT Culture/DFA): 940 specimens (aggregated from UAB: 351, JHU: 192, SUNY: 220, UCSF: 177).
  • Total (CT/GC Positive/Culture Negative): 431 specimens (aggregated from UAB: 101, JHU: 12, SUNY: 81, UCSF: 236, SJH: 1).
  • Total (Mixed Symptomatic/Asymptomatic): 261 specimens (aggregated from UAB: 7, JHU: 94, SUNY: 8, SJH: 152).
  • Total (Asymptomatic Patients, Dacron Swab Only): 190 specimens (aggregated from UAB: 1, JHU: 10, SUNY: 2, UCSF: 1, SJH: 176).

• Data Provenance: The study was a "multicenter study," indicating data collected from multiple clinical sites (UAB, JHU, SUNY, UCSF, SJH). The specific country of origin is not explicitly stated, but the institution names (e.g., UAB, JHU, SUNY, UCSF) strongly suggest United States. The study appears to be prospective or a collection of clinical samples, as it evaluates the diagnostic performance of the new test against a reference method on specimens. The text does not explicitly state "retrospective" or "prospective" but the context of a new device validation implies prospective data collection for clinical performance.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications

The document does not explicitly state the number or specific qualifications of experts used to establish the ground truth. However, the ground truth method relies on:

• Cell Culture: This is a laboratory-based method.
• DFA (Direct Fluorescent Antibody): This is a microscopy-based method that typically involves trained microbiologists or laboratory personnel to interpret results.
• PCR (Polymerase Chain Reaction): Used for "discordant analysis" or further testing in specific cases. PCR also requires skilled laboratory personnel.

While "experts" in the sense of physicians or radiologists making clinical diagnoses are not explicitly mentioned for establishing the ground truth, the "gold standard" methods (cell culture and DFA) implicitly rely on highly trained and qualified laboratory professionals to perform and interpret the tests accurately.

4. Adjudication Method for the Test Set

The document does not describe a formal "adjudication method" in the sense of multiple human readers independently reviewing cases and then coming to a consensus (e.g., 2+1 or 3+1).

Instead, the ground truth was established by a composite reference standard: Cell Culture/DFA. For cases where the HCII CT-ID test result was discordant with the Cell Culture/DFA result, PCR was often used for further investigation. For example, the notes mention "CT-ID+/Cul-/DFA- Tested Positive by PCR" with specific counts, indicating that PCR was used to resolve discrepancies and refine the understanding of true positives/negatives in challenging cases. This implies a form of discrepancy resolution rather than a multi-reader adjudication per se.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

No, a multi-reader multi-case (MRMC) comparative effectiveness study comparing human readers with and without AI assistance was not done. This study is evaluating a standalone diagnostic test (the Digene HCII CT-ID Test), not an AI-assisted interpretation tool for human readers.

6. Standalone Performance Study (Algorithm Only)

Yes, a standalone performance study was done. The entire study described evaluates the performance of the Digene HCII CT-ID Test itself (an in-vitro diagnostic device/assay), without human-in-the-loop interpretation once the assay is run and the RLU values are generated. The interpretation of RLU values into positive/negative/equivocal is based on a defined algorithm and cutoff values. The reported sensitivity, specificity, NPV, and PPV are for the device operating in this standalone manner.

7. Type of Ground Truth Used

The primary ground truth used was a composite reference standard consisting of:

• Cell Culture: Considered the "gold standard" for Chlamydia trachomatis detection at the time.
• DFA (Direct Fluorescent Antibody): Used in conjunction with cell culture, likely as a confirmatory test if cell culture was inconclusive or for direct detection from samples.
• PCR (Polymerase Chain Reaction): Used for further investigation and discrepancy resolution, particularly for specimens where the HCII CT-ID test gave a positive result but the Cell Culture/DFA was negative (e.g., "CT-ID+/Cul-/DFA- Tested Positive by PCR"). This suggests that PCR served as a higher-level reference in ambiguous cases.

8. Sample Size for the Training Set

The document does not specify the sample size for a training set. This is a clinical validation study for a medical device (an in-vitro diagnostic kit). The reported data appears to be from a validation or test set. For such IVD assays, development often involves extensive internal testing and optimization (which could be considered a form of "training" or assay development phase), but this document focuses on the final clinical performance validation.

9. How the Ground Truth for the Training Set Was Established

Since a distinct "training set" with established ground truth is not mentioned in the provided text, this question cannot be answered from the available information. The document focuses on the performance of the developed assay against a reference standard in a clinical test set.

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