(14 days)
The STRATIFY JCVTM Antibody ELISA testing service provided by Focus Diagnostics is intended for the qualitative detection of antibodies to John Cunningham virus in human serum or plasma. The assay is intended for use in conjunction with other clinical data, in multiple sclerosis and Crohn's disease patients receiving natalizumab therapy, as an aid in risk stratification for progressive multifocal leukoencephalopathy development. The assay is for professional use only and is to be performed only at Focus Diagnostics' Reference Laboratory.
The assay is not intended for donor screening. The performance of this assay has not been established for use in other immunocompromised patient populations or in neonates and pediatrics patient populations.
The STRATIFY JCV™ Antibody ELISA consists of two devices. The first is an initial detection ELISA and the second device is a confirmatory (inhibition) ELISA. Both tests utilize the same recombinant antigen which is used in two different formats as described in section L. The devices include the following reagents; Recombinant JC virus like particles (VLP), a JCV high and low positive controls, consisting of human sera that is positive for JCV antibodies, and JCV negative control consisting of human sera that is negative for JCV antibodies. The conjugate, substrate, wash buffers and blocking buffers needed for the test are not supplied with the device and are listed together with other reagents and consumables in the device labeling.
Here's a breakdown of the acceptance criteria and the studies that support the performance of the STRATIFY JCV™ Antibody ELISA, based on the provided 510(k) summary:
Acceptance Criteria and Reported Device Performance
| Acceptance Criteria Category | Acceptance Criteria | Reported Device Performance (Summary) |
|---|---|---|
| Precision (Detection Assay) | Total % CV should be acceptable for intended clinical use. | Total % CV ranged from 7.0% to 18.3% for plasma, and 9.1% to 12.9% for serum. |
| Precision (Detection Assay - Indeterminate) | Indeterminate samples should consistently yield indeterminate results. | Serum indeterminate pool returned indeterminate 96.7% (87/90) of the time; plasma indeterminate pool returned indeterminate 100% of the time. |
| Precision (Confirmation Assay) | Indeterminate samples, when confirmed, should consistently yield positive results. | Serum indeterminate pool confirmed positive 100% (86/86) of the time; plasma indeterminate pool confirmed positive 100% (90/90) of the time. |
| Analytical Specificity (Cross-Reactivity - Spiked Antibodies) | No observed reactivity with common cross-reacting antibodies. | No observed reactivity (0/3 detected for each) with antibodies to E. coli, M. tuberculosis, and Pneumocystis jiroveci. |
| Analytical Specificity (Cross-Reactivity - Seroprevalence) | JCV seroprevalence in groups with other antibodies should not be significantly higher than expected background. | Three groups (C. pneumoniae, HSV1, T. pallidum) exhibited slightly higher positivity than expected the normal population, but no direct cross-reactivity was explicitly proven in this study design. M. pneumoniae showed lower. |
| Analytical Specificity (Interferences - Endogenous Substances) | Signal change due to interferents should not alter result interpretation. | Most interferents (Albumin, Ascorbic Acid, Cholesterol) showed acceptable shifts. Triglyceride, Hemoglobin, and Bilirubin in plasma, and Hemoglobin and Bilirubin in serum, demonstrated >20% shift from baseline, indicating potential interference. |
| Analytical Specificity (Interferences - Concomitant Medications) | Concomitant medications should not interfere with JCV antibody detection. | No potential interfering effect was observed for commonly used medications (Paracetamol, Ibuprofen, Methylprednisolone, Amoxicillin, Acetylsalicylic Acid, Multi-Vitamin, Amantadine, Diclofenac) based on longitudinal analysis in patient cohorts. |
| False Negative Rate (JCV Viruric Patients) | False negative rate should be low and acceptable. | Initial assessment from STRATA study: 2.5% (95% CI: 0.5 to 4.9%) based on 5/204 viruric patients. Confirmed in STRATIFY-1 study: 2.7% (95% CI: 0.9 to 6.2%) based on 5/186 viruric patients. |
| Method Comparison (with LDT) | Acceptable agreement with a laboratory-developed test. | Positive Percent Agreement (PPA) of 91.0% (122/134) with 95% CI: 85.0% to 94.8%. Negative Percent Agreement (NPA) of 89.4% (59/66) with 95% CI: 79.7% to 94.8%. |
| Matrix Comparison (Serum vs. Plasma) | Qualitative results from serum and plasma should show equivalence. | 100% (50/50) qualitative agreement between paired serum and plasma samples. Mean % difference for nOD values was 4.9%. Regression slope was 0.99 (95% CI: 0.9695 to 1.0103) and intercept 0.0 (95% CI: -0.0034 to 0.0043). |
| Clinical Performance (PML Risk Stratification) | High sensitivity for JCV antibodies in PML patients prior to diagnosis. Ability to stratify PML risk. | 100% sensitivity (37/37) with 95% CI: 90.6% to 100% in pre-PML samples from natalizumab-treated patients. JCV antibody positive status results in a 1.82-fold increased risk of PML. |
Study Details
2. Sample size used for the test set and the data provenance:
- Precision Studies (Detection & Confirmation):
- Sample Size: 90 aliquots for each plasma and serum level (High Positive, Indeterminate, Low Positive, Negative) in the detection assay. The indeterminate pools then subjected to confirmation (90 plasma indeterminate, 86 serum indeterminate).
- Data Provenance: Not explicitly stated, but likely from laboratory internal samples/controls, potentially spiked to achieve different concentrations.
- Analytical Specificity (Cross-Reactivity - Spiked Antibodies):
- Sample Size: 3 replicates for each of 3 spiked antibodies (total 9 tests for serum, 9 for plasma).
- Data Provenance: Laboratory, using commercially available human antibodies spiked into JCV negative serum/plasma.
- Analytical Specificity (Cross-Reactivity - Seroprevalence):
- Sample Size: Panels of up to twenty remnant specimens (e.g., 20 for C. pneumoniae, HSV6, VZV, Candida, HSV1, HSV2; 4 for T. pallidum; 9 for M. pneumoniae; 15 for CMV; 20 for HIV1). Total 188 samples across various sero-positive groups.
- Data Provenance: Remnant clinical specimens, likely retrospective from various patient populations.
- Analytical Specificity (Interferences - Endogenous Substances):
- Sample Size: Not explicitly stated as a number of samples, but involved spiking a single low-concentration JCV antibody native serum and plasma panel with various interferents and comparing to baseline.
- Data Provenance: Laboratory, using native serum/plasma samples and spiked interferents.
- Analytical Specificity (Interferences - Concomitant Medications):
- Sample Size: Subset of 585 MS patients from the AFFIRM study.
- Data Provenance: Prospective clinical trial (AFFIRM study) data, with serial samples collected over 30 months. Patients were treated for Multiple Sclerosis.
- False Negative Rate (JCV Viruric Patients):
- STRATA Study: 204 viruric patients.
- STRATIFY-1 Study: 186 urinary JCV DNA positive subjects (out of 1073 total subjects).
- Data Provenance: Prospective clinical studies (STRATA and STRATIFY-1), involving MS patients.
- Method Comparison with LDT:
- Sample Size: 200 samples (62 negative, 71 low positives near cut-point, 67 positive).
- Data Provenance: Not explicitly stated, but presumably clinical samples, likely retrospective.
- Matrix Comparison:
- Sample Size: 50 paired plasma and serum samples.
- Data Provenance: Clinical samples (presumably from patients).
- Clinical Performance (PML Risk Stratification - Pre-PML Samples):
- Sample Size: 37 available serum samples from confirmed PML patients.
- Data Provenance: Retrospective collection of serum samples from patients who developed PML, collected specifically from clinical trials and post-marketing reports prior to PML diagnosis.
- Clinical Performance (PML Risk Stratification - MS Population JCV Positivity):
- Sample Size: 5,896 MS patients.
- Data Provenance: Clinical trials (AFFIRM, TYGRIS-US, STRATIFY-1) and a national MS registry (Sweden). This is a large, geographically diverse, retrospective and potentially prospective (from ongoing studies) cohort of MS patients.
- Clinical Performance (JCV Antibody Prevalence - CD Patients):
- Sample Size: 313 CD patients.
- Data Provenance: Two completed Phase 3 clinical trials (CD301 and CD303) of natalizumab in Crohn's disease patients. Retrospective.
3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts:
- The document does not mention the use of experts to establish ground truth for the test sets (patient samples, viruric samples, etc.). The ground truth for these studies relies on other laboratory methods (e.g., urinary JCV DNA positivity for viruric patients) or clinical diagnoses (e.g., confirmed PML diagnosis for the pre-PML samples).
4. Adjudication method for the test set:
- The document does not describe an adjudication method involving experts for any of the test sets. Ground truth is established by laboratory results (e.g., confirmed urinary JCV DNA positivity) or clinical diagnosis of PML, not by expert consensus on the samples themselves.
5. If a multi reader multi case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance:
- No. This is an ELISA (Enzyme-Linked Immunosorbent Assay) for detecting antibodies, not an imaging device or AI-assisted diagnostic tool that would involve human readers. Therefore, an MRMC study is not applicable and was not performed.
6. If a standalone (i.e. algorithm only without human-in-the loop performance) was done:
- Yes, effectively. The STRATIFY JCV™ Antibody ELISA is a laboratory assay. Its performance characteristics (precision, specificity, false negative rates, and clinical performance) are evaluated as a standalone test, meaning the results are generated directly by the assay without real-time human interpretation or modification of the assay output. Human intervention occurs in performing the assay and interpreting the final quantitative (nOD, % Inhibition) or qualitative (Positive/Negative/Indeterminate) results based on predefined cut-offs.
7. The type of ground truth used:
- JCV Viruric Patients: JCV DNA positivity in urine (confirmed infection).
- PML Risk Stratification: Clinical diagnosis of Progressive Multifocal Leukoencephalopathy (PML), along with historical records of natalizumab treatment and prior immunosuppressant use.
- Method Comparison: The Laboratory Developed Test (LDT) served as the comparative method, acting as a de facto reference in that specific study.
- For other analytical studies (precision, cross-reactivity, interference), ground truth was established by known concentrations/statuses of analytes or known presence/absence of cross-reactants/interferents.
8. The sample size for the training set:
- The document does not explicitly describe a "training set" in the context of a machine learning algorithm. This is a traditional IVD ELISA kit.
- However, the cut-off for the assay (nOD > 0.25 positive,
§ 866.3336 John Cunningham Virus serological reagents.
(a)
Identification. John Cunningham Virus serological reagents are devices that consist of antigens and antisera used in serological assays to identify antibodies to John Cunningham Virus in serum and plasma. The identification aids in the risk stratification for the development of progressive multifocal leukoencephalopathy in multiple sclerosis and Crohn's disease patients undergoing natalizumab therapy. These devices are for adjunctive use, in the context of other clinical risk factors for the development of progressive multifocal leukoencephalopathy.(b)
Classification. Class II (special controls). The special control for this device is the FDA guideline document entitled “Class II Special Controls Guideline: John Cunningham Virus Serological Reagents.” For availability of the guideline document, see § 866.1(e).