Abstract
We examined the effect of endogenous immunoglobulins (G, A and M) and albumin on the measurement of thyroid hormones by different methods, including a new non-isotopic immunoassay of free thyroxine (FT4) and free triiodothyronine (FT3), in a large number of patients with non-thyroidal illness (NTI). Variations in serum protein concentrations can affect the results of radioimmunoassay of human thyroid hormones and thyroxine binding globulin (TBG). Our data revealed that in patients with non-thyroidal illness, when fluctuations in serum γ-globulin occurred the T3/TBG and T4/TBG ratios altered. Consequently, when patients are suffering from non-thyroidal illness with changing γ-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 γ-globulin levels. A recently developed enhanced luminescense enzyme immunoassay for FT3 and FT4 (Amerlite FT3 and FT4 kits) provides more reliable and accurate results, because of its resistance to interference, espeically from albumin and γ-globulin.
