Abstract
An external quality assessment survey of testing facilities in UK clinical laboratories for the detection of drugs of abuse was made with nine freeze-dried samples of urine containing representative drugs with their metabolites from the following seven classes; amphetamines and stimulants, barbiturates, cannabinoids, cocaine, minor tranquillisers, opiates and non-opiate narcotics. Reports were received from 120 laboratories. Thirty six per cent of laboratories reported on all seven drug classes and 71% on the five classes excluding cannabinoids and cocaine. A single drug screening technique was used by 32% of laboratories whilst 46% were able to perform tests by both immunological and chromatographic techniques. There was a mean level of false positive reporting of 4·3% and an observed level of false negative reports of 8·4%, the latter underestimating the true frequency. The minor tranquillisers, cocaine and benzoyl ecgonine were the most frequently missed analytes. Several false reports had important potential implications for patient care.