Prevalence of abnormal thyroid function test results in patients with acute medical illnesses.

We measured serum total and free thyroxine (T4) and triiodothyronine (T3) concentrations, free T4 and T3 indexes, thyroid-stimulating hormone (TSH), thyroxine-binding globulin (TBG) and thyroxine-binding prealbumin (TBPA) concentrations in 98 patients hospitalized for acute medical illnesses. The free thyroxine index (FT4I) or TSH level was abnormal in 16 percent, but only 3 percent had thyroid disease. Serum fre T4 measurements by equilibrium dialysis were abnormal in 25 percent, but no additional patients who initially had abnormal concentrations of serum free T4 were subsequently proved to have thyroid disease. Patients with supranormal serum free T4 concentrations (21 percent) ahd higher serum T4, lower serum T3, and higher serum reverse T3 (rT3) concentrations than other patients, but the measured changes in serum T4, TBG and TBPA levels could only partly account for the magnitude of the free T4 elevation. In these acutely ill patients, an accurate diagnosis of thyroid disease could be achieved by determination of FT4I and TSH level and a history of medication usage. We conclude that other tests are rarely necessary for this purpose in a patient population such as this.