Abstract
BACKGROUND
High-throughput fentanyl immunoassays have recently emerged for clinical use, but early reports have demonstrated relatively high false-positive rates. The purpose of this study was to compare 2 immunoassays, the ARK and ARK II fentanyl immunoassays, and to demonstrate the clinical impact of implementing the ARK II assay.
METHODS
The ARK and ARK II fentanyl assays were performed on a Roche c 502 chemistry analyzer. Positive and negative percentage agreement was assessed for each assay with 112 residual patient specimens relative to liquid chromatography-tandem mass spectrometry (LC-MS/MS). Cross-reactivity was assessed with the primary metabolite, norfentanyl, and analogs acetylfentanyl, acrylfentanyl, and furanylfentanyl. The proportion of specimens that did not confirm was assessed retrospectively from the laboratory information system.
RESULTS
The concordance of the ARK assay was 75% (kappa 0.46, 95%CI 0.28-0.63) and the ARK II was 93% (kappa 0.86, 95%CI 0.76-0.95) with LC-MS/MS. 30 ng/mL of norfentanyl was required for a positive result by ARK and 15 ng/mL by ARK II. Similar cross-reactivity was observed when fentanyl and norfentanyl were both present in the specimen and with fentanyl analogs. After implementing the ARK II assay, the proportion of specimens that did not confirm by LC-MS/MS decreased from 11.7% per month to 2.0% per month.
CONCLUSIONS
The ARK II fentanyl immunoassay has improved concordance relative to the original ARK fentanyl immunoassay using LC-MS/MS as the comparator method. Improved analyte specificity resulted in a reduced proportion of clinical samples that do not confirm. Impact StatementHigh-throughput fentanyl immunoassays are available for clinical use, but the false-positive rate is relatively high at ∼10%-14%. Here we assess the ARK II fentanyl immunoassay and demonstrate better concordance relative to mass spectrometry than the original ARK assay. Clinical implementation of the ARK II assay led to a reduction in samples that were falsely positive from 11.7% using the ARK assay to 2.0%. Improvements to the original ARK fentanyl assay are likely to reduce false-positive fentanyl screens and reduce unnecessary confirmatory assays.
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