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Osteomark NTx Point of Care (POC) is a urinary assay for the quantitative measure of the excretion of cross-linked N-telopeptides of type I collagen (NTx) normalized to urinary creatinine (nM Bone Collagen Equivalents/mM creatinine). The test is used to monitor bone resorption changes following initiation of antiresorptive therapy (e.g., hormone replacement therapy).

The Osteomark® NTx POC device is a single-use, disposable four-channel reflectance photometer integrated with dry reagent chemistry strips and contained within a sealed plastic case. Each unit consists of:

• an optics subassembly that also supports the reagent strips .
• electronics, batteries, photodetectors, and light emitting diodes (LEDs). ●
• . plastic parts
• two reagent strips ●
• a desiccant ●
• a liquid crystal display (LCD) ●
  The reagent strips capillary transport with various chemical reactions. The first strip is an immunoassay for measuring the NTx, and the second strip is a general chemistry assay for measuring the creatinine. In both strips, a blue color is measured in discrete test zones. The test zones are the areas where the specific reaction occurs and concentrations are measured.
  The NTx reaction proceeds as follows: anti-NTx antibody, conjugated to blue microparticles, migrate across the strip upon the addition of urine sample. The amount of blue microparticles captured on the test zones is proportional to the amount of NTx in the sample.
  The creatinine reaction proceeds as follows: the addition of the urine sample solubilizes enzymes immobilized in the strip test zones. A cascade of enzymatic reactions mediates the production of hydrogen peroxide from the oxidation of creatinine. In the presence of horseradish peroxidase and a color indicator, a blue color is generated from the hydrogen peroxide with an intensity proportional to the concentration of creatinine in the sample.
  The LEDs and silicon photodetectors compare the reflectances of the color intensities before and after the sample addition. Based on the calibration parameters stored in memory, the numerical concentrations of NTx and creatinine are calculated. Assay results are expressed in nM Bone Collagen Equivalents (BCE) divided by mM creatinine (nM BCE/mM creatinine).

Here's a breakdown of the acceptance criteria and study information for the Metrika DRx® NTx (Osteomark® NTx Point of Care) device, based on the provided 510(k) summary:

Acceptance Criteria and Device Performance

Note regarding Acceptance Criteria: The document does not explicitly state numerical acceptance criteria for many metrics. The "Implied Acceptance Criteria" column infers what might be considered acceptable based on typical clinical assay performance or the statement that studies "demonstrated substantial equivalence." The FDA's successful clearance implies that the reported performance was deemed acceptable.

Study Details

1. Sample size used for the test set and the data provenance:

   • Accuracy Study: 235 urine samples.
     • Provenance: This dataset was used for comparative testing between Osteomark® NTx POC and the two predicate methods. The samples were assayed by Osteomark® NTx POC across three "POLtype" clinical sites (Physician Office Laboratories) and by the predicate methods at a reference laboratory. It is implied these were prospective samples collected for the purpose of the study, given they were tested at clinical sites. The country of origin is not specified but is implicitly the USA given the FDA submission.
   • Clinical Performance (HRT Monitoring): 200 samples from 50 HRT-treated women.
     • Provenance: Retained samples from a published study. This indicates a retrospective analysis of previously collected samples. Country of origin not specified.

2. Number of experts used to establish the ground truth for the test set and the qualifications of those experts:

   • Accuracy Study: The ground truth for the accuracy study was established by predicate methods (Osteomark® NTx EIA and Creatinine Plus) performed at a reference laboratory. These are established analytical methods, not subjective expert assessment. Therefore, no human "experts" in the traditional sense (e.g., radiologists) were used to establish ground truth for this aspect. The expertise lies in the validated predicate assays themselves.
   • Clinical Performance (HRT Monitoring): The ground truth for comparing NTx changes and correlation with BMD comes from the reference method (Osteomark NTx EIA) and Bone Mineral Density (BMD) measurements. Again, these are objective measurements, not subjective expert interpretation.

3. Adjudication method for the test set:

   • Not applicable. The ground truth was established by laboratory measurements using predicate devices and BMD measurements, not through expert consensus requiring adjudication.

4. 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, a multi-reader multi-case (MRMC) comparative effectiveness study was not done. This device is an in-vitro diagnostic (IVD) assay that provides quantitative measurements, not an AI-assisted diagnostic imaging device requiring human reader interpretation. Therefore, the concept of human readers improving with/without AI assistance does not apply.

5. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done:

   • Yes, the device itself provides a standalone result (NTx/creatinine ratio). The accuracy and precision studies evaluate the performance of this device in isolation, comparing its output to predicate methods. While a professional user operates the device, the device's measurement and calculation of the final result (NTx/creatinine) are entirely automated ("algorithm only"). The intended use states "professional use," indicating human operation, but the core analytical performance is standalone.

6. The type of ground truth used (expert consensus, pathology, outcomes data, etc):

   • Analytical Ground Truth: For accuracy and linearity, the ground truth was established by measurements obtained from legally marketed predicate devices (Osteomark® NTx EIA and Creatinine Plus) in a reference laboratory setting.
   • Clinical Ground Truth: For the HRT monitoring study, the ground truth included measurements from the predicate Osteomark NTx EIA and Bone Mineral Density (BMD) measurements, which are established clinical outcome measures for bone health.

7. The sample size for the training set:

   • The document does not explicitly mention a "training set" in the context of machine learning or AI. This device is a quantitative assay based on dry reagent chemistry and reflectance photometry, not a machine learning algorithm that requires a distinct training phase. Therefore, the concept of a training set for an AI model is not applicable here. The assay's internal calibration parameters are "stored in memory," suggesting a pre-determined calibration process rather than an adaptive training set.

8. How the ground truth for the training set was established:

   • As there is no "training set" in the context of an AI/ML algorithm, this question is not applicable. The device relies on established scientific principles of immunoassay and enzymatic reactions with internal calibration.

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