Factors associated with the quality of laboratory performance in the United Kingdom external quality assessment scheme for serum growth hormone

Abstract

A search was made for associations between poor performance in the UK External Quality Assessment Scheme (EQAS) for serum growth hormone (GH), and a range of factors including assay method, laboratory workload and staffing, and Internal Quality Control (IQC) procedures. On the basis of the factors identified as being associated with poor performance we recommend the following. 1. Laboratories using RIA for GH should routinely analyse samples at two dilutions and report a mean result. 2. The use of 125I-GH which is 5 or more weeks old should be avoided. Tracer should also be chromotographed to remove aggregate before use. 3. Laboratories using RIA should avoid using a standard curve which covers too wide a range of concentration; a curve midpoint (ie GH concentration to reduce the zero standard binding by 50%) of about 8 mU/l or less is probably acceptable. 4. It should be noted that high workloads present a risk of some loss in quality of performance. 5. An experienced member of staff other than the assayist should be responsible for checking IQC data. 6. Laboratories which do not have the resources to maintain fully their own RIA as outlined above should carefully consider use of an unbiased, precise IRMA. The UK EQAS has identified two assays (Boots-Cell-tech Sucrosep, NETRIA) that appear to meet these criteria [2]. The above observations may also be relevant to immunoassays for other peptide hormones.