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The AxSYM® Cortisol assay is a Fluorescence Polarization Immunoassay (FPIA) for the quantitative measurement of Cortisol in human serum, plasma or urine on the AxSYM® System to aid in the diagnosis and treatment of adrenal disorders.

The AxSYM Cortisol assay utilizes Fluorescence Polarization Immunoassay (FPIA) technology. The AxSYM Cortisol Reagents and sample are pipetted in the following sequence:

• Sample and all AxSYM Cortisol Reagents required for one test are pipetted by the sampling probe into various positions of a Reaction Vessel (RV).
• Sample, the Cortisol Antiserum (antibody), pretreatment solution and Solution 4 (Line Diluent) are pipetted into one well of the RV.
• Additional pretreatment solution 4 (Line Diluent) are pipetted to the cuvette of the RV.
• The RV is immediately transferred into the Processing Center. Further pipetting is done in the Processing Center by the Processing Probe.
  In the processing center, an aliquot of the predilution mixture and Solution 4 (Line Diluent) are transferred to the cuvette of the RV and the blank intensity of the sample is measured. A second aliquot of the predilution mixture is transferred to the cuvette along with the Cortisol Fluorescein Tracer. Cortisol from the sample and the Cortisol Fluorescein Tracer compete for binding sites on the antibody molecule. The intensity of polarized fluorescent light is measured by the FPIA optical assembly.

Here's a breakdown of the acceptance criteria and the study that proves the device meets them, based on the provided text:

Acceptance Criteria and Device Performance

Study Details:

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

   • Reproducibility (Precision) Study: Three buffer-based panel members (1, 2, and 3) were assayed, in replicates of two, at two separate times per day, for 20 days. This means each panel member had 80 measurements (2 replicates * 2 times/day * 20 days).
   • Comparison Study:
     • 130 endogenous and cortisol-spiked serum and sodium heparin plasma specimens.
     • 150 endogenous and cortisol-spiked urine specimens.
   • Expected Values Study:
     • 50 serum specimens (AM and PM collections).
     • 49 urine specimens (24-hour collection).
   • Data Provenance: Not explicitly stated (e.g., country of origin). The studies appear to be prospective, as samples were "tested using the AxSYM Cortisol assay" and "collected from apparently healthy individuals" for the expected values study.

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

   • Not applicable as this is an in-vitro diagnostic (IVD) device measuring a biomarker, not interpreting imaging or clinical data that would require expert consensus. The "ground truth" for the comparison study is the result obtained from the predicate device (Beckman Access® Cortisol assay).

3. Adjudication method for the test set:

   • Not applicable. The "ground truth" for the comparison study is the result from the predicate device.

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:

   • Not applicable. This is an IVD device, not an AI-based imaging or
     diagnostic device that involves human readers interpreting results.

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

   • Yes, the performance characteristics (reproducibility and comparison studies) reflect the standalone performance of the AxSYM® Cortisol assay without human-in-the-loop performance. The "human-in-the-loop" for this type of device would involve laboratory technicians performing the test, but the performance metrics provided are for the assay itself.

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

   • For the comparison study, the ground truth was the results obtained from the predicate device (Beckman Access® Cortisol assay).
   • For the reproducibility study, the "ground truth" is inherent to statistical precision analysis from repeated measurements.
   • For the expected values study, the "ground truth" was the cortisol levels measured by the device itself in apparently healthy individuals to establish reference ranges.

7. The sample size for the training set:

   • Not explicitly stated. For an IVD device, there isn't typically a "training set" in the same sense as machine learning algorithms. The development of the assay reagents and parameters would involve extensive R&D, but specific "training set" sizes are not usually disclosed in 510(k) summaries as they are not a discrete dataset used to train an algorithm.

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

   • Not applicable, as there's no explicitly defined "training set" with ground truth in the context of an IVD like there would be for an AI algorithm. The development process would rely on established biochemical principles and extensive internal testing/optimization.

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