LOW T4 AND LOW FT4I IN SERIOUSLY ILL PATIENTS - CONCISE COMMUNICATION

Abstract

Of 128 euthyroid hospitalized patients with nonthyroidal illnesses (NTI), 33% had a low total thyroxine (T4). Of the latter patients, 43% had a low free T4 index [FT4I]. In euthyroid patients with NTI, free T4 was, with rare exceptions, within the range for well euthyroid controls. The free T4, as determined by 2 different radioimmunoassays, was diagnostically low in 34 of 37 hypothyroid patients without NTI. However, in hypothyroid patients with NTI, the free T4 determination was less informative. Only 4 of 10 patients had a low free T4 by the Corning test, and none of ten were low by the Clinical Assays test. Patients with NTI frequently have low T4 and low FT4I, despite being euthyroid. Low free T4 strongly suggests hypothyroidism but normal free T4 in patients with NTI does not exclude hypothyroidism.