Fingerstick Plasma Drug Testing of Chronic Pain Patients: Comparison of Paired Fingerstick Plasma and Urine Specimens

Aim A clinical study was conducted to evaluate fingerstick blood as a viable biological matrix for monitoring prescription and illicit drugs in a clinical setting on patients undergoing pain and addiction treatment. The current standard for monitoring patients’ medication use, misuse, and diversion is urine drug testing (UDT). Materials and Methods This study compared 632 paired urine and fingerstick blood specimens collected at three pain management clinics and one suboxone clinic for 35 drugs and/or metabolites. Plasma from the fingerstick blood was used for the analysis. The urine and plasma specimens were analyzed by validated liquid chromatography–tandem mass spectrometry (LC-MS-MS) procedures. The urine cutoff used by most pain testing laboratories were used to identify positive and negative drugs in urine. Limit of quantitation was used to identify positive and negative drugs in plasma. Drugs and/or metabolites were quantified in both urine and plasma using deuterium-labeled internal standards. Results Results were tabulated for urine and plasma specimens for data analysis. The results showed that 8.7% of plasma specimens detected more drugs compared to the corresponding urine specimens, and 2.2% of the urine specimens detected a drug that was negative in the corresponding plasma specimen. Overall 89.1% of the specimens had complete agreement between urine and plasma specimens for detection. The observed Cohen’s Kappa value for overall drug detection was 0.96 an “almost perfect” agreement as characterized by Landis and Koch. Conclusion Based on the observed data, the authors conclude that plasma collected from fingerstick blood is a better matrix to monitor patients currently prescribed pain medications or patients currently undergoing medication-assisted opioid treatment compared to urine drug testing.