One possible reason for this ethnic difference is that cocaine metabolites have been detected at a higher rate in African American hair than in other racial groups, which appears independent to specific laboratory procedures (
Cone & Joseph, 1996;
Welp et al., 2003).
The so-called “racial bias” hypothesis (Kidwell, Lee, & DeLauder, 2000) is consistent with the observation that cocaine (but not benzoylecgonine) demonstrates differential affinity to different hair types based on melanin subtype, with dark-color hair demonstrating the greatest affinity (Borges, Roberts, Wilkins, & Rollins, 2003). However, several studies reported conflicting or mixed results on the “racial bias” hypothesis (e.g.,
Hoffman, 1999;
Kelly, Mieczkowski, Sweeney, & Bourland, 2000;
Mieczkowski & Newel, 2000).
We attempted to control for several hair conditions. Hair treatment, the use of body hair rather than head hair, and short hair sample were not significantly related to apparent underreporting of cocaine when other measures are simultaneously controlled for. The adjusted odds ratio of 5.89 for hair treatment did not reach a statistical significance (p= .053).
One critical review concluded that cosmetic hair treatments tend to result in more false negatives (Kintz, Cirimele, & Ludes, 2000). Hair color or melanin information was not collected in our study, however. A consensus is needed on toxicological aspects of hair color and treatment in hair drug testing, given that hair drug testing has become widely-used for employment screening.