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Immunoassay for the in vitro quantitative determination of phenytoin in human serum and plasma.

The CEDIA® Phenytoin II Assay is based on the bacterial enzyme Bgalactosidase, which has been genetically engineered into two inactive fragments. These fragments spontaneously reassociate to form fully active enzyme that, in the assay format, cleaves a substrate, generating a color change that can be measured spectrophotometrically.

In the assay, phenytoin in the sample competes with analyte conjugated to one inactive fragment of ß-galactosidase for antibody binding site. If analyte is present in the sample, it binds to antibody, leaving the inactive enzyme fragments free to form active enzyme. If analyte is not present in the sample, antibody binds to analyte conjugated on the inactive fragment, inhibiting the reassociation of inactive ß-galactosidase fragments, and no active enzyme is formed.

This document describes the CEDIA® Phenytoin II Assay, a homogeneous enzyme immunoassay for the quantitative determination of phenytoin in human serum and plasma. The K963840 submission compares this new assay to a predicate device, the CEDIA® Phenytoin Assay (K905689), and other commercially available products.

Here's an analysis of the acceptance criteria and study information provided:

1. Table of Acceptance Criteria and Reported Device Performance

The submission does not explicitly state "acceptance criteria" for each performance characteristic with pre-defined thresholds. Instead, it presents performance data for the CEDIA® Phenytoin II Assay and compares it to the predicate CEDIA® Phenytoin Assay or another commercially available method (Abbott TDx® Phenytoin). The implication is that performance comparable or superior to these predicate devices constitutes acceptable performance for substantial equivalence.

• Level (Sample): 6.30 (N=120), Within-Run %CV: 3.2, Total %CV: 5.1
• Level (Control 2): 14.80 (N=120), Within-Run %CV: 2.0, Total %CV: 3.1
• Level (Control 3): 26.75 (N=120), Within-Run %CV: 1.3, Total %CV: 2.3
  (Comparison to CEDIA® Phenytoin Assay: Low 10.7 (N=120), Within-Run %CV: 3.6, Total %CV: 4.7; Mid 17.7 (N=120), Within-Run %CV: 2.0, Total %CV: 3.8; High 35.4 (N=119), Within-Run %CV: 1.5, Total %CV: 3.3) |
  | Lower Detection Limit | ≤ 0.6 µg/mL (matching TDx Phenytoin) | 0.6 µg/mL |
  | Linearity | Range of 0.6 - 40.0 µg/mL (matching TDx Phenytoin) | 0.6 - 40.0 µg/mL |
  | Method Comparison | Strong correlation (r > 0.99) and agreement with predicate devices (CEDIA® Phenytoin and Abbott TDx® Phenytoin), with a slope close to 1 and intercept close to 0. | Vs CEDIA® Phenytoin (N=114):
• Least Squares: y = 1.00x - 0.17, r = 0.998, SEE = 0.55
• Deming's: y = 1.00x - 0.19, r = 0.998, SEE = 0.39

Vs Abbott TDx® Phenytoin (N=92):

• Least Squares: y = 0.984x - 0.10, r = 0.994, SEE = null |
  | Interfering Substances | No significant interference at or above specified concentrations of bilirubin, hemoglobin, lipemia, total protein, and rheumatoid factor. | No interference at:
• Bilirubin: 66 mg/dL (Improved from 50 mg/dL for predicate)
• Hemoglobin: 1000 mg/dL (Same as predicate)
• Lipemia: 1000 mg/dL (Same as predicate)
• Total Protein: 12.0 g/dL (Slightly less than 13 g/dL for predicate)
• Rheumatoid Factor: 100 IU/mL (Less than 180 IU/mL for predicate) |
  | Specificity (% Cross-reactivity) | Comparable or better (lower) cross-reactivity for structurally similar compounds (HPPH, 5-MPPH) compared to the predicate device. | - HPPH: 1.8% (Slightly higher than 1.4% for predicate)
• 5-MPPH: 5.7% (Higher than 4.8% for predicate) |

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

• Precision:
  • For the CEDIA® Phenytoin II Assay, N=120 for each of the three levels (Sample, Control 2, Control 3).
  • For the predicate CEDIA® Phenytoin Assay, N=120 for Low and Mid levels, and N=119 for the High level.
• Method Comparison:
  • Vs CEDIA® Phenytoin: N=114
  • Vs Abbott TDx® Phenytoin: N=92
• Data Provenance: The document does not explicitly state the country of origin or whether the data was retrospective or prospective. Given that it's a 510(k) submission for a new assay, the data is almost certainly prospective as it's generated specifically for the submission. The origin is implied to be from Boehringer Mannheim Corporation, likely from studies conducted in the USA where the company is based.

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

This type of information is generally not applicable to a quantitative immunoassay device. The "ground truth" for these tests comes from samples with known concentrations (e.g., controls, spiked samples) or from reference methods (the predicate devices in this case). There are no human "experts" establishing a subjective ground truth for the test results.

4. Adjudication Method for the Test Set

Not applicable. As described above, this is a quantitative assay, and "adjudication" by experts is not a relevant concept for determining the ground truth for chemical measurements. The comparison is between analytical results.

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

No. An MRMC study is relevant for diagnostic imaging or subjective interpretations where multiple human readers interpret cases. This submission is for a quantitative immunoassay, which does not involve human readers interpreting images or cases, nor does it describe human-in-the-loop performance.

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

Yes, the entire performance evaluation presented is a standalone (algorithm/device-only) performance. The assay measures phenytoin levels quantitatively. There is no human intervention or interpretation of the assay's direct output (spectrophotometric readings) that would constitute a "human-in-the-loop" component.

7. The Type of Ground Truth Used

The ground truth used for performance evaluation appears to be:

• Known concentrations: For precision studies, control materials with known phenytoin concentrations are used. For linearity, samples with varying known concentrations are typically prepared.
• Reference method results: For method comparison, the results from the CEDIA® Phenytoin Assay (the predicate) and the Abbott TDx® Phenytoin (another established method) serve as the reference or "ground truth" against which the new assay's measurements are compared.

8. The Sample Size for the Training Set

The document does not provide details on a "training set" in the context of machine learning, because this is an immunoassay, not an AI/ML algorithm that requires a training set of data. The development of the assay reagents and parameters would involve optimization and calibration, but this is distinct from a "training set" for an AI model.

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

Not applicable, as there is no mention or indication of an AI/ML-based "training set" for this immunoassay device. The development process would involve establishing accuracy and performance characteristics using various laboratory methods, certified reference materials, and comparative studies.

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