Minor alterations in thyroid - Function tests associated with diabetes mellitus and obesity in outpatients without known thyroid illness

Thyroid function tests might be affected by diabetes and obesity. To evalua te the influence of these parameters in routine conditions, 72 diabetic and 53 non-diabetic outpatients without known thyroid diseases or severe chron ic illness were recruited over a 7 - month period. For each patient, dosage s of thyrotropin (TSH), total and free thyroxine (TT4 and FT4, respectively ), total and free triiodothyronine (TT3 and FT3) and T3 resin uptake (T3RU) were performed by radioimmunoassays. The simultaneous influence of various parameters known to affect thyroid-function tests was evaluated by multiva riate linear regression. The studied variables included gender, age, glucos teroids, estrogens, tobacco habits, iodine contacts, body mass index (BMI) and diabetes mellitus. Tobacco habits and iodine contacts did not influence any tests. As expected, estrogens induced an increase in TT4 and TT3 value s (p<0.001 and 0.020, respectively) associated with a decrease in T3RU (p<0 .001). Consequently, females had lower T3RU than males (p<0.0001). Corticot herapy was associated with decreased TSH values (p=0.022). TT3 and FT3 decr eased with age (p<0.001), whereas T3RU and FT4 increased (p=0.020 and 0.004 , respectively). In contrast to an increase in TSH (p=0.006), TT4 and FT4 d ecreased at higher BMI levels (p=0.018 and 0.004, respectively), which is c onsistent with subclinical hypothyroidism. In diabetic patients, TSH was lo wer than in nondiabetic subjects (p=0.039). Thus, the present study indicat es that besides known parameters such as age and drugs, thyroid-function te sts can also be altered by diabetes mellitus and obesity.