Determination of hair ketamine cut-off value from Hong Kong ketamine users by LC-MS/MS analysis

Ketamine is one of the most frequent abused drugs in Hong Kong and South-East Asia, and the cases of ketamine abused have been reported worldwide. Hair has been commonly used as a specimen for the proof of chronic drug abused because of its non-invasiveness and long detection windows. The determinations of ketamine in hair with varieties of state-of-the-art instruments and detection methods have been developed in the past decade; however, the cut-off value for ketamine abuser has not been developed according to the international guidelines. The aim of this study is to propose a cut-off value for ketamine in hair by analyzing ketamine and its metabolite norketamine by LC-MS/MS method in a population of ketamine users in Hong Kong. The limit of detection (LOD) and limit of quantification (LOQ) for ketamine and norketamine were 20 pg/mg and 100 pg/mg, respectively. From 977 ketamine abusers, the cut-off value for ketamine in hair was proposed to be 400 pg/mg of hair. This proposed cut-off value is the concentration of hair ketamine when over 90% of samples are being detected with the presence of norketamine, which is a proof of ketamine abuse. This value could be applied as a screening or occupational cut-off for reference.