Evaluation of immunochemical drug screenings of whole blood samples. A retrospective optimization of cutoff levels after confirmation-analysis on GC-MS and HPLC-DAD

Four commonly used immunoassay kits were evaluated for their efficiency in screening for drugs of abuse in whole blood. Six groups of illicit drugs (opiates, cannabinoids, amphetamines, cocain and benzoylecgonine, benzodiazepines, and methadone) were determined by using the homogenous assays ADx and CEDIA DAU and compared with the results produced by means of the inhomogenous assays MTP and Pyxis 24. The measured 86 blood samples were taken from authentic routine analyses between February and September, 2000. Chromatographic confirmation analyses were carried out in all cases (positive and negative immunochemical pretesting). The cutoff levels were retrospectively optimized to reduce false-negative results with priority. Furthermore, false-positive pretests were minimized in order to decrease laboratory work under economical aspects. Specificity and sensitivity were determined for each parameter and assay. For the ADx assay, specificities of 54% (cannabinoids) to 97% (cocaine and metabolite) and sensitivities of about 67% (amphetamine class) to 94% (opiates) were found. The CEDIA assay revealed specificities of 77% (methadone) up to 100% (benzodiazepines) and 75-96% sensitivities for amphetamines and opiates. The MTP immunoassay resulted in specificities of 52% (methadone) to 95% (opiates, cocain, and metabolite) and sensitivities of 92% (amphetamines) up to 100% (methadone). The evaluation of the Pyxis 24 resulted in specificities of 70-96% (benzodiazepines and amphetamines) and sensitivities of 75% (amphetamines) up to 100% (cannabinoids and methadone), respectively. In conclusion, the microtiterplate immunoassays revealed higher sensitivities and have proved to be at an advantage detecting the lowest concentrations of drugs. However, especially for clinical applications in emergency cases with acute intoxications, when screening results are urgently required, homogenic assays such as ADx or Cedia provide preferable alternatives with faster and easier handling. © Oxford University Press 2001.