Quality control in parathyroid hormone radioimmunoassays: a multicentre study performed by the European Parathyroid Hormone Study Group

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Abstract
The results of the 2nd collaborative study of radioimmunological parathyroid hormone (PTH) determination in 22 serum samples performed by 24 laboratories in the European PTH Study Group (EPSG) are reported. Radioimmunoassay systems can yield results that are clinically relevant in the differential diagnosis of hypercalcemia. It also emphasizes that numerical values generated by a spectrum of different immunoassay systems cannot be compared directly. Numerical values can be compared if the same reagents and method, provided as a kit, are used. Using their in house reagents, 14 of 20 laboratories discriminated between low and normal iPTH [immunoreactive parathyroid hormone] serum, 11 of them between normal and marginal hyperparathyroid sera, 17 of them between normal and grossly hyperparathyroid sera. Four laboratories agreed to a ranking order of serum samples, which was expected to cover all ranges on an average standard calibration curve; 6 were mistaken once, and 10 two or more times. Using the kit, all participants but one discriminated between sera with low, normal, marginal and grossly elevated PTH, and all agreed to the above ranking order of these sera. As far as these criteria are concerned, there was no relation between the quality of results, obtained with in house reagents, and differences in antisera (but one, which was an anti-human 1-34 PTH antiserum), methods of tracer preparation and peptides used for tracer preparation. Few laboratories, using bovine PTH standards, were able to satisfy the above described conditions; all of the laboratories, using human PTH standard preparations, did so with minor exceptions.

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