[Radioimmunoassay and its problems: quality, sources of error and quality control of in vitro procedures for thyroid...

A review is made of methodical aspects of the performance of radioimmunoassays with special regard to the determination of T3, T4, TSH and free thyroxine. The quality of the analytical systems is determined by specificity, sensitivity, correctness and accuracy. To ensure quality, guidelines are given for the procedure of obtaining test samples as well as for the transport and storage; furthermore, the dependence of the results on the employed method is documented. For determination of the normal range particular emphasis has to be given to the methodical details, regional differences and the age of the patients. To ensure quality, the most frequent sources of error have to be known. These are listed for the determination of thyroid hormones, TSH, thyroxine-binding globulin, thyroglobulin and for the T3U-test; a critical review of the methods is added. Suggestions are given for the systematic internal control of quality; a method for continuous control by a computer program is presented.