CLINICAL-EVALUATION OF ACCURACY IN DETERMINING SERUM FREE-THYROXINE AND FREE TRIIODOTHYRONINE IN PATIENTS WITH NONTHYROIDAL ILLNESS - IMMUNOGLOBULIN EFFECT ON T3 TBG RATIO AND T4/TBG RATIO/

We examined the effect of endogenous immunoglobulins (G, A and M) and albumin on the measurement of thyroid hormones by different methods, i ncluding a new non-isotopic immunoassay of free thyroxine (FT4) and fr ee triiodothyronine (FT3), in a large number of patients with non-thyr oidal illness (NTI). Variations in serum protein concentrations can af fect the results of radioimmunoassay of human thyroid hormones and thy roxine binding globulin (TBG). Our data revealed that in patients with non-thyroidal illness, when fluctuations in serum gamma-globulin occu rred the T3/TBG and T4/TBG ratios altered. Consequently, when patients are suffering from non-thyroidal illness with changing gamma-globulin levels, clinical scientists should take care when they use T3/TBG and T4/TBG ratios as a substitute for FT3 or FT4 estimation. We found FT4 and FT3 (determined with Amerlex-M kits) T3 and the T3/TBG ratio were altered inversely due to the difference in the serum gamma-globulin l evels. A recently developed enhanced luminescense enzyme immunoassay f or FT3 and FT4 (Amerlite FT3 and FT4 kits) provides more reliable and accurate results, because of its resistance to interference, especiall y from albumin and gamma-globulin.