A Comparative Analysis of Two Commonly Used FDA-Approved Immunoassays for Fentanyl Detection.

BACKGROUND: Given the opioid epidemic, fentanyl screening in urine has become increasingly important. Immunoassays remain the most common screening methodology due to the high throughput and ease of integration into automated chemistry systems. The fentanyl ARK II from Ark Diagnostics is a widely used immunoassay, while a novel fentanyl assay called FEN2 by Lin-Zhi has become available on the Roche platform. Here, we evaluate and compare their performance. METHODS: Four hundred and thirty-four urine samples were analyzed for fentanyl across the Lin-Zhi FEN2 and ARK II assays on the Cobas c502 platform. Samples were analyzed immediately upon request for drug of abuse screening or frozen for subsequent analysis. For confirmation testing, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method with a limit of detection of 1 ng/mL for fentanyl/norfentanyl was used. Any sample with either fentanyl or norfentanyl above the LC-MS/MS cutoff was deemed positive. RESULTS: The ARK II had 11 false negatives and 7 false positives, while the Lin-Zhi FEN2 had 12 false negatives and 2 false positives. This resulted in ARK II having a sensitivity and specificity of 90.4% and 97.8% respectively, while Lin-Zhi FEN2 had a sensitivity and specificity of 89.5% and 99.4%. CONCLUSIONS: Both the ARK II and Lin-Zhi FEN2 immunoassays detected fentanyl well. Overall, the Lin-Zhi assay had slightly better specificity than ARK II, in our data set. While some discrepant results were observed between the 2 immunoassay systems, most occurred near the immunoassay detection cutoffs.

A case of false positive opiate immunoassay results from rifampin (rifampicin) treatment.

The drug screen test on a 12-year-old male patient was positive for opiates by a kinetic interaction of microparticles in solution (KIMS) immunoassay method on the Roche Cobas C502. The positive opiates result was not confirmed by the liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. A chart review revealed that the patient had tuberculosis and was on rifampin. We spiked rifampin into drug-free urine and tested opiates with the Cobas method. Once again, a positive result was obtained. This case showed that rifampin can still cause false positive opiate results measured with the KIMS method. We want to stress the importance of confirming positive screen results by more specific methods such as LC-MS/MS.

Calculation of the estimated glomerular filtration rate using the 2021 CKD-EPI creatinine equation and whole blood creatinine values measured with Radiometer ABL 827 FLEX.

OBJECTIVES: Estimated glomerular filtration rate (eGFR) can be calculated using serum/plasma creatinine measured with automated chemistry analyzers. It is unclear whether eGFR can be calculated using creatinine values measured in whole blood (WB creatinine). The aim of this study is to determine the comparability between the eGFR calculated using WB creatinine and plasma creatinine. METHODS: Blood samples from 1,073 patients presented to the emergency department (ED), perioperative areas, intensive care unit (ICU) or nuclear medicine were used to determine the accuracy of WB creatinine. For each sample, WB creatinine was first measured with Radiometer ABL827 FLEX blood gas analyzer, then plasma creatinine was measured with Roche Cobas702 chemistry analyzer after samples were centrifuged. In a subset of 247 samples with the information of age and sex, whole blood eGFR (WB eGFR) and plasma eGFR were calculated using WB creatinine and plasma creatinine and the 2021 chronic kidney disease epidemiology collaboration (CKD-EPI) creatinine equation, respectively. RESULTS: WB creatinine correlated with plasma creatinine linearly with a slope of 1.06 and an intercept of -0.01. The coefficient of determination (R2) was 0.99. WB eGFR correlated with plasma eGFR linearly with a slope of 0.95, intercept of -1.63, and R2 of 0.97. Comparing to plasma eGFR, the sensitivity and specificity for WB eGFR to identify those with high risk (eGFR<30 mL/min/1.73 m2) and low risk (eGFR>45 mL/min/1.73 m2) for kidney injuries was 100 and 92.2%, respectively. The overall concordance in classifying the four stages of kidney damage between WB eGFR and plasma eGFR was 87.9%. CONCLUSIONS: WB creatinine measured with Radiometer ABL827 Flex can be used to calculate eGFR using the 2021 CKD-EPI creatinine equation. The sensitivity and specificity for WB eGFR to identify those with high and low risks for potential kidney injuries are acceptable in patients needing rapid assessment of their kidney functions.

Evaluation of 2 Batched Pretreatment Systems for the Measurement of Whole Blood Tacrolimus on the ARCHITECT Immunoassay Analyzer.

BACKGROUND: Measurement of tacrolimus using the ARCHITECT immunoassay analyzer requires a manual extraction step that puts clinical laboratory workers at risk for ergonomic injury. Therefore, we developed 2 batched extraction systems for tacrolimus measurement on the ARCHITECT analyzer and describe their features herein. METHODS: Two batched extraction methods were developed at 2 different laboratories. The batched extraction methods allow processing of at least 20 specimens at a time. We evaluated the analytical performance of those methods and compared them with the United States Food and Drug Administration (FDA)-cleared process for manually extracting individual specimens. RESULTS: Comparing the performance of batched- and individual-extraction methods revealed that both methods had comparable between-day imprecision, high patient-results correlation (R2 values ≥0.9869), equivalent functional sensitivity (0.48 ng/mL), and good linearity between 1 ng per mL and 25 ng per mL. Further, we observed decreased delta check-identified errors using the batched method. CONCLUSION: The 2 developed batched extraction methods for tacrolimus measurement that we describe herein demonstrate excellent performance and can replace individual specimen extraction.