External quality assessment of laboratory performance in analysis of toxicological cases

A mean of 44 members of the United Kingdom national external quality assess ment scheme (UKNEQAS) for toxicology reported analytical findings on 10 tox icological cases circulated between December 1995 and February 2000. Materi al distributed usually consisted of a 5 ml blood and a 20 ml urine sample s imulated by quantitative addition of drugs and their metabolites to materia l donated by volunteers and patients. The samples were accompanied by a bri ef outline of the circumstances surrounding the case. Laboratories were req uested to report their analytical findings, list methods of analysis, and p rovide interpretation of their findings. The mean overall success rate for identification of drugs or their pharmacological group was 76%, failure bei ng largely by laboratories providing an immunoassay-based screening service for a fixed range of drug groups. The latter laboratories indicated that c ases would be referred to regional toxicology centres for further investiga tion or confirmation. The coefficient of variation of measurements was <7% for routine analytes, such as ethanol and paracet-amol, but 26-44% for tric yclics and opiates. There were 3% false positive reports. The quantity and content of interpretative comment provided by the laboratories was very var iable. A number provide nothing in addition to the analytical result. (C) 2 001 Elsevier Science Ireland Ltd. All rights reserved.