An inter- and intralaboratory quality-control survey of radioimmunoassay of insulin, thyroxin, thyrotropin, cortisol, digoxin, gastrin, beta 2-microglobulin, and IgE in Japan with commercially available kits.

Abstract

We report results of a quality-control survey of radioimmunoassay (RIA) of eight analytes, participated in by 249 laboratories of various types throughout Japan. For the purpose of the external control survey, lyophilized specimens containing two different concentrations of each analyte were sent to the participating laboratories, which supplied both their assay values and their raw data for the standard curves and for the samples. The individual data for the standard curve were analyzed by the RIA data-processing program described by Faden and Rodbard. The precision profile obtained for the individual assay was used as the estimate of the quality of each assay. Although there was a wide scatter in assay values, the quality of the assay by the individual laboratories was not the major contributor to this scattering, because the values they reported for the assays and precision profiles of the standard curves were almost identical with those obtained from the kit manufacturers. When the reported assay values were analyzed according to the brand of kits, by analysis of variance, the treatment mean square due to difference in the make of the kits significantly exceeded the error mean square due to "within-kit" variation in the assay of insulin, thyroxin, thyrotropin, cortisol, gastrin, and digoxin. The CVs for "between-kit," "within-kit," "between-assay" and "within-assay" variations (the latter two aspects were studied in a representative laboratory, for convenience of comparison) were about 20, 15, 13, and 7%, respectively. Because the observed within-kit variation is of almost the same magnitude as that expected from the combination of within-assay and between-assay variation, the skill of the users probably was equal and the accuracy and precision of the kits probably had the greatest impact on assay variation. This survey also emphasizes the criteria for commercially available RIA kits.