• Yungkang Lee, Keane K Y Lai, and S M Hossein Sadrzadeh.
• Department of Pathology and Laboratory Medicine, Cedars-Sinai Medical Center, Los Angeles, CA 90048, United States. Electronic address: hugolee@alumni.usc.edu.
• Clin. Biochem. 2013 Aug 1; 46 (12): 1118-1124.

BackgroundThe lack of specificity of immunoassays for drugs of abuse testing (DAT), and concerns over its cost in conjunction with reflex confirmatory tests prompted us to investigate the combinatorial use of dried urine spot (DUS) and LC-MS/MS as an alternative.MethodsThe method development and validation were performed in accordance with the guidelines published by FDA and CLSI.ResultsIn this study we established and validated the precision, accuracy, and linearity of our DUS-LC-MS/MS method, and assessed the recovery, interference, and carryover as well. The linearity check for all 19 analytes demonstrated slopes between 0.94 and 1.04, and R(2) always greater than 0.99. Between-batch CV for QC at 4 difference levels ranged from 1.1% to 10%, where CV of LLOQ ranged from 1.2% to 12.8% and CV of ULOQ ranged from 0.8% to 5.1%. A concordance study with patient specimens between our method and GC-MS demonstrated 80.8% to 100% agreement. Stability of DUS specimens was assessed up to 30 days and the measured concentrations ranged from 94% to 114% of the 100 ng/mL urine calibrator used for this assessment.ConclusionsWe established and validated a DUS-LC-MS/MS method for DAT that conforms to the guidelines dictated by FDA, CLSI, and SAMHSA. While our method with high sensitivity and specificity provides an alternative diagnostic utility to EMIT immunoassays, it also offers superior solutions in specimen transportation, preservation, and storage. The benefits of our method are apparent in reducing turnaround time and test costs that result in better patient care.Copyright © 2013 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.

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