[The effect of nonthyroidal diseases on the serum hormone level of the thyroid gland function regulation cycle]

Thyroid hormone serum concentrations were measured in clinically apparently euthyroid patients suffering from diseases that have symptoms in common with thyroid dysfunction. The diseases investigated were: anorexia nervosa (n = 13), myocardial infarction (n = 13) cirrhosis of the liver (n = 19), terminal renal insufficiency (n = 30) and rheumatoid arthritis (n = 14). In each group, the patients were divided into groups according to the degree of their disease. A relative decrease in 3,5,3'-triiodothyronine (TT3) serum levels is the most pronounced effect of all the non-thyroidal ailments investigated. Individual observations show that total and free thyroxine levels can also be lowered by some acute illnesses. Moreover, the extent of the decrease in TT3 serum levels depends significantly on the severity of the non-thyroidal illness. This phenomenon was observed in all ailments investigated. Based on our findings it is concluded that the diagnosis of thyroid dysfunction may be extremely difficult in many non-thyroidal illnesses. This study should help the clinician to evaluate laboratory hormone data correctly in respect to the diagnosis of thyroid dysfunction in patients with non-thyroidal illnesses.