A comparison of commercially available luminescence enhanced enzyme immunoassays with in-house non-radioisotopic assays for thyroxine binding globulin and total thyroxine

Commercial luminescence enhanced enzyme immunoassays (Amersham-Amerlite) for thyroxine binding globulin (TBG) and total thyroxine (TT4) were compared with the in-house methods (TT4--Abbott TDx, TBG--Immunoluminometric Assay (ILMA)). The experimental groups consisted of 108 healthy euthyroid blood donors, 165 non-selected thyroid outpatients, 44 tumour bearers and 84 haemodialysis patients. Total thyroxine/thyroxine binding globulin quotients were constructed as an index of thyroid function. The luminescence enhanced enzyme immunoassays were precise (interassay coefficients of variation less than 10% in the range 5-45 mg/l thyroxine binding globulin and 20-100 micrograms/l for total thyroxine) performed similarly to the in-house methods in the differentiation of eu-, hypo- and hyperthyroidism on the basis of total thyroxine/thyroxine binding globulin quotients. Although statistically significant differences often occurred in comparisons of the in-house method with the luminescence enhanced enzyme immunoassays, these only gave rise to thyroid status differences in two cases out of 273, where the in-house method gave a hyperthyroid, the luminescence enhanced enzyme immunoassay a euthyroid answer, when taken from the total thyroxine/thyroxine binding globulin quotients. The luminescence enhanced enzyme immunoassays performed as well as the in-house methods, and quality assessment data were comparable with their radioimmunological counterparts.