Problematic determination of serum growth hormone: Experience from external quality assurance surveys 1998–2003

Abstract

The objective of the present study was to start a new external quality assurance survey (EQAS) for the determination of serum growth hormone (GH) using pooled serum specimens as quality‐assurance samples. To give good coverage of multiple forms of GH, the specimens included sera from GH‐deficient and acromegalic patients as well as from persons showing a normal response in GH provocation tests. In one survey the quality‐control specimens were spiked with exogenous 22‐kD GH to obtain some idea of the specificity and GH recovery of the assays. The EQA surveys of 1998–2003 were organized by Labquality of Helsinki in cooperation with three university hospital laboratories in Finland. The number of participating laboratories ranged from 8 to 14. During 1998–2003, gratifying methodological harmonization occurred in the participating group, as the participants switched to the immunometric detection principle, the number of method applications decreasing from 7 to 3. In 1998 the 14 participating laboratories reported five different conversion factors (from µg/l to mU/l), whereas in 2003 7 of the 8 participants reported the same factor. Despite the harmonization trend among participating laboratories, further efforts are needed, because marked method‐based differences still exist. This dialogue should include kit manufacturers, laboratory experts, EQA organizations and clinicians using the test results.