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Osteomark® NTx Serum EIA provides a quantitative measure of cross-linked Ntelopeptides of type I collagen (NTx) in serum as an indicator of human bone resorption. Serum NTx level is used to aid in predicting skeletal response (bone mineral density) to antiresorptive therapy and in monitoring bone resorption changes following initiation of antiresorptive therapy. Prior to initiating antiresorptive therapy, serum NTx level is used to determine the probability for a decrease in bone mineral density after one year in postmenopausal women treated with hormonal antiresorptive therapy relative to those treated with calcium supplement.

The Osteomark NTx Serum EIA is a competitive-inhibition enzyme-linked immunosorbent assay (ELISA/EIA) for quantitative determination of NTx present in human serum. NTx is adsorbed to a 96-well microplate: Diluted samples are added to the microplate wells, followed by a horseradish peroxidase labeled monoclonal antibody. NTx in the specimen competes with the NTx epitope on the microtiter plate for antibody binding sites. Following a wash step, the amount of labeled antibody bound is measured by colorimetric generation of a peroxide substrate. NTx concentration is determined spectrophotometrically and calculated using a standard calibration curve. Assay values are reported in nanomoles Bone Collagen Equivalents per liter (nM BCE).

The Osteomark NTx Serum EIA is a competitive-inhibition enzyme-linked immunosorbent assay (ELISA/EIA) designed for the quantitative determination of NTx in human serum. This assay is used to predict skeletal response to antiresorptive therapy and to monitor changes in bone resorption after therapy initiation. It also helps determine the probability of bone mineral density decrease in postmenopausal women on hormonal antiresorptive therapy versus those on calcium supplements.

1. Table of Acceptance Criteria and Reported Device Performance

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

The document describes several studies:

• Reference Range Studies:
  • Premenopausal Women: N = 257 (multi-center, cross-sectional study at five regional sites). The country of origin is not specified but implied to be the US given the FDA submission. This was a prospective study to determine reference ranges.
  • Men: N = 176 (multi-center, cross-sectional study at three regional sites). The country of origin is not specified but implied to be the US. This was a prospective study to determine reference ranges.
• Intra-subject Variability Studies:
  • Postmenopausal Women: n=271 (short-term), n=261 (long-term). Provenance not specified. Retrospective/Prospective not specified for this specific study, but the overall context suggests prospective data collection in clinical settings.
  • Men: n=32 (short-term), n=27 (long-term). Provenance not specified. Retrospective/Prospective not specified for this specific study.
• Assay Reproducibility and Precision Studies:
  • Intra-assay variability: Four human serum specimens. Provenance not specified. Not directly tied to a clinical population, but rather assay samples.
  • Inter-assay variability: Eight human serum specimens. Provenance not specified. Not directly tied to a clinical population, but rather assay samples.
  • Total assay precision: Level I Serum Control and Level II Serum Control tested at four clinical laboratories. Provenance not specified. These are control materials, not patient samples.
• Antigen Recovery: Nine serum specimens. Provenance not specified. These are assay samples.
• Dilutional Linearity: Five serum specimens. Provenance not specified. These are assay samples.
• Clinical Studies (HRT):
  • Postmenopausal Women treated with HRT: The study enrolled a cohort of postmenopausal women. The baseline NTx mean was 15.9 nM BCE. Post-treatment mean was 12.2 nM BCE. While a specific N for the HRT group is not provided in this summary, the context suggests a clinical trial. The study results (Reference 4) indicate the source is likely from U.S. clinical trials. This was a prospective clinical trial.
• Clinical Studies (Bisphosphonate):
  • Postmenopausal Women treated with Bisphosphonate: The study was conducted at a regional specialty hospital in the northeast United States. The study was randomized and double-blind. N is not explicitly stated in the summary, but it involved women randomized to either placebo or alendronate. This was a prospective clinical trial.

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

The document does not describe the use of human "experts" to establish ground truth for the device performance studies in the traditional sense of a diagnostic interpretation.

For the clinical efficacy studies (HRT and Bisphosphonate), the "ground truth" was clinical outcomes:

• Bone Mineral Density (BMD) changes: Measured by objective methods (e.g., DEXA scans) over time. This is an objective clinical measurement, not expert consensus on an image or test result.
• Response to therapy: Defined by changes in NTx levels and subsequent changes in BMD.

4. Adjudication Method for the Test Set

Not applicable. The reported studies evaluate the analytical performance of the assay and its correlation with clinical outcomes (BMD changes), not the interpretation of results by human readers requiring adjudication.

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

No. The Osteomark NTx Serum EIA is an in-vitro diagnostic assay for quantitative measurement. It does not involve human readers interpreting images or data where AI assistance would be relevant for a MRMC study.

6. Standalone (Algorithm Only Without Human-in-the-Loop Performance) Study

Yes, implicitly. The performance characteristics (variability, recovery, linearity) and the clinical utility of the assay itself (e.g., "Osteomark NTx Serum EIA mean baseline values... fell significantly after 3 months of therapy") are reported as standalone performance of the diagnostic kit. There is no human-in-the-loop component for the assay's execution or the interpretation of the numerical NTx values for these studies. The physician uses the derived NTx value in clinical management.

7. Type of Ground Truth Used

• Analytical Performance: The ground truth for analytical performance (variability, recovery, linearity) is based on established laboratory analytical methods and expected theoretical values for spiked samples or diluted controls.
• Clinical Studies: The ground truth for the clinical studies (HRT and Bisphosphonate) is outcomes data and objective clinical measurements:
  • Bone Mineral Density (BMD) assessed after one year.
  • Changes in NTx levels post-therapy. This is an outcome of the intervention, not an externally established ground truth for the device itself.

8. Sample Size for the Training Set

The document describes the device performance validation and clinical studies. There is no description of a "training set" in the context of machine learning (AI) for this diagnostic assay. The terms "training set" and "test set" are not applicable in the typical AI sense to this type of in-vitro diagnostic device. Instead, the studies cited relate to establishing reference ranges and validating analytical and clinical performance.

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

Not applicable, as no "training set" in the AI sense is described. The analytical and clinical performance data were established through direct laboratory measurements and clinical trial outcomes, respectively, as outlined above.

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