Analytic Performance of Immunoassays for Drugs of Abuse Below Established Cutoff Values

Abstract

Background:The analytic performance and accuracy of drug detection below Substance Abuse and Mental Health Services Administration (SAMHSA) cutoffs is not well known. In some patient populations, clinically significant concentrations of abused drugs in urine may not be detected when current SAMHSA cutoffs are used. Our objectives were to define the precision profiles of three immunoassay systems for drugs of abuse and to evaluate the accuracy of testing at concentrations at which the CV was <20%. Methods: Drug-free urine was supplemented with analytes to assess the precision in three commercial drugs-of-abuse immunoassay systems below the SAMHSA-dictated cutoffs for amphetamines, opiates, benzoylecgonine, phencyclidine, and cannabinoids. Consecutive urine samples with signals associated with a CV <20% by Emit ® immunoassay and below SAMHSA cutoffs were then subjected to confirmatory analysis. Results: The CV of all immunoassay systems tested remained <20% to drug concentrations well below SAMHSA cutoffs. The accuracy of urine drug-screening results between the SAMHSA-specified cutoffs and the precision-based cutoffs was less than accuracy for specimens above the SAMHSA cutoffs, but the use of the precision-based cutoff produced a 15.6% increase in the number of screen-positive specimens and a 7.8% increase in the detection of specimens that yielded positive results on confirmatory testing.

Laboratory Testing for Prescription Opioids

“…Most clinical laboratories still use the 300 ng/mL of morphine as the cutoff concentration for a positive opioid screen; however, the effectiveness of this cutoff concentration in the detection of intoxication or aberrant opioid use has not been rigorously evaluated in many clinical settings in which it is generally used. This threshold was also developed in adult populations and may not be appropriate for children who produce less concentrated urine [17]. Lower thresholds have been advocated in the pain medicine setting [18].…”

Is This Drug Screen Really Negative? Special Investigation of Drug Screening in Pediatrics

“…Hattab et al (2) did a similar study with lower cutoffs for cocaine, opiates and cannabinoids, and found that 74%, 84%, and 31% of cannabinoids, cocaine metabolites, and opiates, respectively, had a positive confirmation. This result underscores the importance of confirming presumed positive screen results when using a lower cutoff (6).…”

“…For infants and children presenting to an emergency department with altered mental status, suspected child abuse, burns, or other injuries, a urine drug screen is commonly used and provides results with a rapid turnaround time, despite lack of sensitivity and specificity (4). Adding to the difficulty in detection is the fact that if the urine is dilute, as it often is in children, the drug concentration will be even lower and less likely to be detected with the SAMHSA cutoffs (5,6).…”

“…There have been a small number of studies that have investigated the impact of lowering the screening cutoffs for various drugs of abuse and have generally found a decrease in the frequency of false-negative results (2,(6)(7)(8). Luzzi et al (6) evaluated the impact of revised cutoffs for amphetamines, cannabinoids, cocaine, opiates, and phencyclidine on immunoassay platforms.…”

Differentiation of Amphetamine/Methamphetamine and Other Cross-Immunoreactive Sympathomimetic Amines in Urine Samples by Serial Dilution Testing

“…Amphetamine immunoassays display precise doseresponse properties from concentrations below the Substance Abuse and Mental Health Services Administration (SAMHSA)-stipulated cutoff to concentrations well above cutoff (8 ). Within this dynamic range, amphetamine and methamphetamine may exhibit dose-response properties that are distinguishable from other cross-immunoreactive compounds.…”