False Positive Drug Results by ELISA Associated with Enzymatic Hair Digestion

Following the experiment that have been designed for immunological screening test followed by a GC-MS confirmation method for the simultaneous analysis of delta-9-tetrahydrocannabinol (9-THC) , 11-nor-9-Carboxy-THC (THC-COOH), 11-Hydroxy-THC (OH-THC), cocaine, benzoylecgonine (BZ) in human hair and avoiding the significant factors responsible for drug degradation by acid and alkali hydrolysis and replace it with enzymatic hair digestion to obtain optimal recovery conditions, that resulted a false positive results after the radioimmunoassay pre-analysis associated with enzymatic hair digestion. Enzymatic hair digestion was used to hydrolyse 18 Turkish samples using proteinase K, Dithiothreitol and Tris HCl buffer. At the beginning 18 out of 18 samples showed to be screened positive on ELISA, towards the end using a threshold of 0.1ng/mg in 50mg hair, 2 positive results were found in 18 cases. It was revealed that the 2 samples were positive for 9-THC and THC-COOH. Cross reaction lead to false positive results in the pre screening step as a result of the degradation of the antibodies in the precoated ELISA micro plate. Sixteen out of 18 positive detections could not be confirmed by GC-MS. In this study we investigated cause behind the drug screening malfunction.