Association between increased concentrations of free thyroxine and unsaturated free fatty acids in non-thyroidal illnesses: role of albumin.

We measured the concentrations of non-esterified free fatty acids and free and total thyroid hormones in serum from patients with various non-thyroidal illnesses (NTI) and chronic renal failure (CRF). The total concentration of free fatty acids was measured enzymatically and the eight most abundant fractions were determined by gas-liquid chromatography. The concentration of total free fatty acids was significantly increased in the NTI group as compared with controls (p less than 0.01); the concentrations of oleic, linoleic and linolenic acid were increased more than those of the other fractions. In NTI the serum-free thyroxine (FT4) concentration was increased (p less than 0.01) and the free triiodothyronine (FT3) concentration was decreased (p less than 0.001); these concentrations were measured by equilibrium dialysis. There was a significant correlation between the levels of total free fatty acids and FT4 in the NTI (n = 43) group (r = 0.45, p less than 0.01), and also between the levels of linoleic acid and FT4 (r = 0.35, p less than 0.05). The serum albumin concentration was decreased in the NTI group, and when free fatty acid to albumin molar ratios were calculated stronger correlations with FT4 were observed (total free fatty acids: r = 0.55; p less than 0.001; oleic acid: r = 0.30, p less than 0.05; linoleic acid: r = 0.46, p less than 0.01; linolenic acid: r = 0.35, p less than 0.05). There was no correlation between FT4 and unsaturated FFA concentrations in CRF patients, who had normal mean FT4 and total FFA levels. These results support the hypothesis that unsaturated fatty acids are involved in the increase of serum FT4 in NTI, especially when albumin levels are low.