Mass spectrometry vs. immunoassay in clinical and forensic toxicology: qui modus in rebus est?

Optimization of biochip assay for illegal substances on drug abusers' whole blood: Randox Evidence vs LC-MS/MS

Immunoassay tests are used in clinical and forensic toxicology laboratories to determine illicit drug use in biological samples. Therefore, this study aims to optimize the cutoff concentrations of DOA I Plus in the blood and compare the LC-MS/MS results. 680 authentic forensic whole blood specimens with Randox Evidence DOA I Plus array were screened for drug of abuse and confirmed by LC-MS/MS. Regarding the manufacturer recommended threshold values, 139 out of 680 authentic blood samples were positive for one or more analytes, while 541 were negative. Nearly all of the 139 positive blood samples confirmed by LC-MS/MS were true positive for one or more analytes, while 522 of the 541 negative blood samples were true negative. The overall sensitivity and the specificity were 87.8% and 99.6%, respectively. THC was considered in detail, and a receiver operator characteristic curve analysis was performed to determine the optimum cutoff for THC, as it accounts for 78% of all positive results according to the manufacturer's recommended thresholds. The optimal threshold value for THC was determined at a concentration of 23 ng/mL, while these values for other parameters were defined as recommended by the manufacturer.

Accuracy evaluation of automated electrochemiluminescence immunoassay for everolimus and sirolimus compared to liquid chromatography-tandem mass spectrometry

Background

We evaluated the analytical performance of a newly developed electrochemiluminescence immunoassay for everolimus and sirolimus compared to that of liquid chromatography‐tandem mass spectrometry (LC‐MS/MS).

Methods

According to Clinical and Laboratory Standards Institute guidelines, the analytical performance including precision, recovery, linearity, and carryover was evaluated. For correlation evaluation, the results of Elecsys^® analysis of everolimus and sirolimus were compared with those of LC‐MS/MS using 120 samples from patients treated with everolimus or sirolimus.

Results

The within‐run and total imprecision values were as follows: 2.3%‐4.5% and 4.5%‐6.4% for the everolimus assay; 3.3%‐4.8% and 4.7%‐8.1% for the sirolimus assay, respectively. The measured concentration was linear over the range of 0.718‐27.585 ng/mL for everolimus analysis and 0.789‐26.880 ng/mL for sirolimus analysis (all R² > 0.99). Recovery was 93.5%‐105.5% for the everolimus assay and 99.2%‐109.1% for the sirolimus assay (except lowest levels). Carryover was −1.09% for the everolimus assay and −0.12% for the sirolimus assay. The results of the two chemiluminescence immunoassays showed acceptable correlations with those of LC‐MS/MS (R = 0.9585 and R = 0.9799, respectively). The two immunoassays showed slightly proportional biases compared to LC‐MS/MS.

Conclusion

Elecsys^® Everolimus and Sirolimus assays showed acceptable analytical performance in precision, linearity, and correlation compared to LC‐MS/MS These methods can be adopted in the clinical laboratory for rapid therapeutic drug monitoring of patients who require treatment with immunosuppressants.