Use of Hair Analysis for Confirmation of Self-Reported Cocaine Use in Users with Negative Urine Tests

Abstract

Identification of cocaine use based on a urine test may miss many cases because of the short elimination half-life of the drug. Our objective was to verify the sensitivity of the cocaine hair test in admitted users. Admitted cocaine users (38), that were 18-70 years of age and reported to have refrained from using cocaine in the few days to months prior to the test, were compared to 10 controls who claimed never to have used cocaine. All had negative urine tests for cocaine and benzoylecgonine by thin-layer chromatography. Cocaine and benzoylecgonine were extracted from unwashed hair and tested by established immunoassays. The hair test was positive in 37/38 cases (97%) and in none of the controls. There was significantly more cocaine in black hair than in brown or blonde hair per mg of cocaine dose reported to have been consumed, highlighting a potential bias when interpreting test results in individuals with dark hair. There was a statistically significant correlation between reported dose used and hair concentrations of cocaine. The cocaine hair test appears to be highly sensitive and specific in identifying past cocaine use in the setting of a negative urine test.