External quality assessment of steroid hormone assays in the United Kingdom.

A brief history of the UK quality assessment schemes and their mode of operation is given, with summaries of overall and method-related performance for each analyte. Cortisol and 17 alpha-hydroxyprogesterone assay performance is very good, but clear differences between methods exist for the former. Both the progesterone and oestradiol schemes demonstrate marked differences between methods. The testosterone scheme is affected by differences in behaviour of direct and extraction methods for specimens from males and females. Results of recovery experiments indicate considerable under-recovery by some direct methods. Future developments and plans for the schemes are described.