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The Psychemedics Microplate EIA for Amphetamine is an enzyme immunoassay (EIA) for the preliminary qualitative detection of amphetamine in human head and body hair using an amphetamine calibrator at 3 ng /10 mg hair cutoff for the purpose of identifying amphetamine use. This is an in vitro diagnostic device intended exclusively for Psychemedics use only. Psychemedics has not performed an evaluation of reproducibility at different laboratories.

The Psychemedics Microplate EIA amphetamine assay provides only a preliminary analytical test result. A more specific alternative chemical method must be used in order to obtain a confirmed analytical result. Gas or Liquid Chromatography/Mass Spectrometry (GC/MS or LC/MS/MS) is the preferred confirmatory method. Clinical consideration and professional judgment should be exercised with any drug of abuse test result, particularly when the preliminary result is positive.

The test consists of two parts; a pre-analytical hair treatment procedure (to convert the solid matrix of hair to a measurable liquid matrix) and the screening assay, the Psychemedics Microplate EIA for Amphetamine. The screening portion of the test system consists of ( 1 ) microplate wells coated with multiple antigens including methamphetamine conjugated to bovine serum albumin (BSA), monoclonal mouse anti-amphetamine, rabbit anti-mouse secondary antibody conjugated to HRP (horseradish peroxidase), substrate [3, 3', 5, 5' tetramethylbenzidine (TMB)], HCl to acidify (and stop the reaction), and wash buffer for washing the plates. Absorbance in the wells is read with a microplate reader.

Here's a breakdown of the acceptance criteria and the study details for the Psychemedics Microplate EIA for Amphetamine in Hair, based on the provided 510(k) summary:

1. Table of Acceptance Criteria and Reported Device Performance

The document doesn't explicitly state "acceptance criteria" with numerical targets in a structured table for diagnostic accuracy (e.g., sensitivity, specificity). Instead, the performance is demonstrated through various studies. The primary comparison is against LC/MS/MS as the confirmatory method. The closest we get to performance criteria are successful precision, cross-reactivity, interference, and environmental contamination studies, as well as substantial equivalence to the predicate device.

Implicit Acceptance Criteria and Reported Device Performance:

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

• Test Set Sample Size:

  • Comparison Testing (EIA vs. LC/MS/MS): 180 samples (comprising both head and body hair).
  • Precision Studies:
    • Intra-Assay: 15 replicates per level (Negative, Cutoff +/- concentrations), totaling 120 samples (8 levels * 15 replicates).
    • Inter-Assay: 75 replicates per level, totaling 600 samples (8 levels * 75 replicates).
  • Cosmetic Treatment Studies: 20 negative samples + 12 positive samples per treatment type (bleach, permanent wave, dye, relaxer, shampoo) for "before and after" comparison. This implies at least 32 distinct samples, each tested multiple times.
  • Environmental Contamination Studies:
    • Aqueous Wash: 11 samples (water-soaked) + 11 samples (saline-soaked)
    • Ethanol Wash: 10 samples (water-soaked) + 13 samples (saline-soaked)
  • Storage & Shipping Stability: 21 amphetamine-positive samples for each study (storage and shipping).
  • Cross-reactivity: MDA, d-amphetamine, PMA, Chloramphetamine, Phentermine, l-amphetamine, MDMA, PMMA, Phenylpropanolamine, Pseudoephedrine, IR, 2S Ephedrine, S,S Pseudoephedrine, Phenylethylamine, MDEA, L-methamphetamine, Ranitidine, Fenfluramine, Mephentermine, Phenmetrazine, Phendimetrazine, Metanephrin (total of 21 named), plus 140 other compounds. Each would have been tested.
  • Interference: 119 compounds.

• Data Provenance: The document does not explicitly state the country of origin or whether the data was retrospective or prospective. Given it's a 510(k) submission to the FDA, it is expected to be from studies conducted under appropriate quality systems, likely in the US, but this is not confirmed. It appears to be prospective data collection for the performance studies described.

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

The ground truth for the comparison testing (diagnostic accuracy) and other analytical performance studies was established using LC/MS/MS (Liquid Chromatography/Mass Spectrometry/Mass Spectrometry) or GC/MS (Gas Chromatography/Mass Spectrometry) as the "preferred confirmatory method."

These methods are highly sensitive and specific analytical techniques widely considered the gold standard for drug detection and quantification. Therefore, the "experts" in establishing this ground truth are the analytical instrumentation and the laboratory personnel qualified to operate and interpret results from LC/MS/MS/GC/MS systems. No human expert consensus was used to establish the ground truth in the clinical sense, but rather the objective biochemical analysis provided by these confirmatory methods.

4. Adjudication Method for the Test Set

No human adjudication method (like 2+1 or 3+1) was explicitly mentioned. The "ground truth" was established purely by the results of the LC/MS/MS or GC/MS confirmatory methods. Discordant results were analyzed and presented. For instance, the table of discordant results shows EIA positive results where LC/MS/MS found 0 amphetamine but identified other substances like phentermine or methamphetamine, suggesting potential cross-reactivity for the EIA.

5. If a Multi Reader Multi Case (MRMC) Comparative Effectiveness Study was Done

No, a Multi-Reader Multi-Case (MRMC) comparative effectiveness study was not done. This would typically apply to scenarios where human readers interpret medical images or complex data, and the AI's role is to assist human interpretation. This device is an in vitro diagnostic (IVD) assay designed for laboratory use, yielding a preliminary qualitative result, not for direct human interpretation in the same way an imaging AI might be. Therefore, the concept of "human readers improving with AI vs. without AI assistance" does not directly apply here. The device provides a preliminary analytical result that then requires chemical confirmation (LC/MS/MS).

6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) was Done

Yes, a standalone (algorithm only) performance study was done. The entire performance summary, including precision, comparison to LC/MS/MS, cross-reactivity, interference, cosmetic treatments, environmental contamination, and stability, assesses the performance of the "Psychemedics Microplate EIA for Amphetamine" assay itself, working in a laboratory setting. The results (Positive/Negative) are generated by the assay system, read by a microplate reader, without human interpretive input that would alter the primary output of the device as an "algorithm." The results are then further interpreted as "preliminary" and require confirmatory methods.

7. The Type of Ground Truth Used

The type of ground truth used was objective chemical confirmatory methods, specifically Gas or Liquid Chromatography/Double Mass Spectrometry (GC/MS or LC/MS/MS). These methods are considered the definitive analytical standard for identifying and quantifying drug substances.

8. The Sample Size for the Training Set

The document does not explicitly mention a "training set" sample size or a training process in the context of machine learning or AI. This is an immunoassay (EIA) device, which is a biochemical test, not typically an AI/machine learning algorithm that requires a training set in the conventional sense. The "training" of such assay systems primarily involves establishing reagents, calibrators, controls, and protocols based on known chemical properties and optimization, rather than ingesting a large dataset of results for algorithmic learning.

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

Since this is an immunoassay and not an AI/ML algorithm, the concept of establishing ground truth for a "training set" as understood in AI development does not apply directly. The development of an immunoassay involves:

• Selection and optimization of antibodies (e.g., monoclonal mouse anti-amphetamine)
• Optimization of reagent concentrations (e.g., BSA conjugates, HRP, substrate)
• Establishing cutoff values (e.g., 3 ng/10 mg hair) through extensive analytical testing and comparison to reference methods (like LC/MS/MS) using known positive and negative samples, as well as samples with varying concentrations.
• Validation of the entire assay system to ensure it performs as intended across various parameters (precision, specificity, etc.), which is what the provided "Summary of Performance Testing" details.

Therefore, the "ground truth" during the development and validation of this EIA assay would have been established using analytically confirmed amphetamine concentrations in hair samples, verified by methods such as LC/MS/MS, to define the assay's performance characteristics and cutoff.

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