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The AMM method is an in vitro diagnostic test for the quantitative measurement of ammonia in human plasma (heparin or EDTA) on the Dimension® clinical chemistry system. Ammonia measurements are used in the diagnosis and treatment of severe liver disorders such as cirrhosis, hepatitis and Reye's syndrome.

The Dimension® Ammonia assay (AMM) is an enzymatic method that uses glutamate dehydrogenase (GLDH) and a stabilized NADPH analog. Ammonia reacts with a-ketoglutarate and reduced cofactor to form L-glutamate and the cofactor. The reaction is catalyzed by glutamate dehydrogenase. The decrease in absorbance due to the oxidation of the reduced cofactor is monitored at 340/700 nm and is proportional to the ammonia concentration.

Here's a summary of the acceptance criteria and the study details for the Dimension® Ammonia Flex® reagent cartridge (AMM), based on the provided 510(k) summary:

Acceptance Criteria and Device Performance

The acceptance criteria for the Dimension® Ammonia Flex® reagent cartridge (AMM) are not explicitly stated as pass/fail thresholds in the provided document. Instead, the document describes the performance characteristics that were "evaluated" or "determined" and compares them to the predicate device or established guidelines. The device demonstrates substantial equivalence based on these performance characteristics.

Here is a table summarizing the reported device performance for key characteristics:

Study Details

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

   • Method Comparison: 127 patient samples for comparison between AMM and predicate AMON.

   • Plasma Comparison: 50 matched lithium heparin and EDTA plasma samples.

   • Reference Interval: 30 healthy adults (17 men and 13 women) for validation of reference interval.

   • Precision: Not explicitly stated as "sample size" but involved multiple runs (20 days, two runs per day, two test samples for each of 3 control levels).

   • Linearity: Not explicitly stated as number of samples, but determined according to CLSI EP-6A which involves multiple dilutions/levels.

   • Analytical Specificity/Interferences: Various concentrations of interferents tested at two ammonia levels (85 µg/dL and 426 µg/dL), and for certain endogenous interferents, patient samples containing the interferent were mixed with a plasma pool. The exact number of samples for each interferent test is not specified, but the methodology follows CLSI EP7-A2.

   • LoB, LoD, LoQ:

     • LoB: 4 samples of calibrator (zero level) over 3 days (1 run/day, 2 replicates/run).
     • LoD: 4 low level samples over 3 days (1 run/day, 2 replicates/run).
     • LoQ: 3 ammonia standards diluted to 17 µg/dL [10 µmol/L] over 3 days (1 run/day, 3 replicates/run).

   • Data Provenance: The document does not explicitly state the country of origin for the patient or control samples. Given Siemens Healthcare Diagnostics, Inc. is based in Newark, DE (USA), it is likely the data were collected in the United States. The studies are described as typically performed by Siemens, indicating prospective collection in a laboratory setting for regulatory submission.

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 for quantitative measurement. The "ground truth" for the test samples is their measured ammonia concentration, determined by established laboratory methods, specifically the predicate device and the new device itself. There are no human expert adjudicators involved in determining the "truth" of an ammonia level.
   • The reference interval (expected values) was validated using the predicate device's established therapeutic range and a literature reference (Textbook of Clinical Chemistry by NW Tietz).

3. Adjudication method (e.g. 2+1, 3+1, none) for the test set:

   • Not applicable. Adjudication methods like 2+1 or 3+1 are typically used in image-based AI studies where human readers might disagree on a diagnosis and a consensus mechanism is needed. For an IVD device, the "truth" value for a sample is its chemical concentration, determined by the measurement system rather than human interpretation or consensus.

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 not an AI-assisted diagnostic imaging device or a device involving human interpretation of results in a clinical read environment. It is an automated in vitro diagnostic test for quantitative chemical measurement.

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

   • Yes, this is essentially a standalone device performance study. The Dimension® Ammonia Flex® reagent cartridge (AMM) is an automated system for quantitative measurement. Its performance characteristics (linearity, precision, interference, LoB/LoD/LoQ, and comparison to a predicate device) are evaluated intrinsically, without human-in-the-loop performance influencing the measurement results themselves. Human involvement would be in operating the instrument and interpreting the numerical output.

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

   • The "ground truth" is established by direct chemical measurement.
     • For Method Comparison, the predicate device (Dimension® Ammonia (AMON)) served as the reference method for comparison.
     • For Precision, commercially available control materials (Liquichek™ Ethanol/Ammonia control) with known target values were used.
     • For Linearity, LoB, LoD, LoQ, studies were performed using calibrators and diluted standards/samples, with the "truth" being the calculated or theoretical concentration values.
     • For Interference studies, the "truth" for bias calculation was the measurement of control samples without the interferent, which then established the baseline against which the interferent's effect was measured.
     • For Reference Interval, the established therapeutic range of the predicate (Dimension® AMON) and a textbook reference (NW Tietz) provided the basis for the expected values.

7. The sample size for the training set:

   • Not applicable in the conventional sense of machine learning/AI models. This is a chemical assay, and thus there is no "training set" like in deep learning for image recognition. The "development" or "optimization" of such an assay involves chemical formulation and engineering, not data-driven model training.

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

   • Not applicable for the reason stated above. The "ground truth" for chemical assays is based on established analytical chemistry principles, reference methods, and certified calibrators/controls, rather than a labeled training set.

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