Oral fluid testing for drugs of abuse: positive prevalence rates by Intercept immunoassay screening and GC-MS-MS confirmation and suggested cutoff concentrations

Abstract

Draft guidelines for the use of oral fluid for workplace drug testing are under development by the Substance Abuse and Mental Health Services Administration (SAMHSA) in cooperation with industry and researchers. Comparison studies of the effectiveness of oral fluid testing versus urine testing are needed to establish scientifically reliable cutoff concentrations for oral fluid testing. We present the results of the first large scale database on oral fluid testing in private industry. A total of 77,218 oral fluid specimens were tested over the period of January through October 2001 at LabOne. Specimens were screened by Intercept immunoassay at manufacturer's recommended cutoff concentrations for the five SAMHSA drug categories (marijuana, cocaine, opiates, phencyclidine, and amphetamines). Presumptive positive specimens were confirmed by gas chromatography-tandem mass spectrometry. A total of 3908 positive tests were reported over the 10-month period, representing a positive rate of 5.06%. Of the five drug categories, marijuana and cocaine accounted for 85.75% of the positives. The pattern and frequency of drug positives showed remarkable similarity to urine drug prevalence rates reported for the general workforce according to the Quest Diagnostics' Drug Testing Index over the same general period, suggesting that oral fluid testing produces equivalent results to urine testing. The data on oral fluid testing also revealed a surprisingly high 66.7% prevalence of 6-acetylmorphine confirmations for morphine positives suggesting that oral fluid testing may be superior in some cases to urine testing. Comparison of oral fluid drug concentrations to SAMHSA-recommended cutoff concentrations in Draft Guidelines indicated that adoption of the screening and confirmation cutoff concentrations of Draft Guidelines #3 would produce the most consistent reporting results for all drug classes except amphetamines. Consequently, it is suggested that the final Guidelines adopt the screening and cutoff concentrations listed in Draft Guidelines #3 with the exception of lowering the amphetamines cutoff concentrations (screening/confirmation) to 50/50 ng/mL for amphetamine and methamphetamine.