Progress and problems in immunoassays for serum pituitary gonadotrophins: evidence from the UK external quality assessment schemes, (EQAS) 1980-1988.

Trends in the quality of assays for serum gonadotrophins performed by laboratories in the UK EQAS during the 1980s are reviewed, with particular reference to the effects of the recent introduction of immunometric assays (IMA) as an alternative to radioimmunoassay (RIA). IMA gave results which were on average 17% higher than RIA for FSH, and 33% lower for LH. These bias characteristics were not entirely accounted for by differences in assay standardisation, but appeared to reflect the different isoforms of the hormones detected by the monoclonal antibodies used in the IMA. Between-laboratory agreement remained, consequently, unsatisfactory overall (geometric coefficient of variation, GCV, 20-30%), although good within method groups (GCV 10%). IMA were less vulnerable to non-specific background interference than many RIA, and could avoid interference from HCG. Some IMA were, however, vulnerable to interference from heterophilic antibodies in patients' sera. The differences between RIA and the various IMA in numerical values reported, and in their vulnerability to interferences underline the need for care in interpreting assay results.