Abnormal thyroid hormone levels in critical nonthyroidal illness

Low levels of thyroid hormone in the absence of clinical hypothyroidism often happen to patients with critical non-thyroidal illnesses (NTI). Low thyroid hormone concentrations in serum do not necessarily mean hypofunction of the thyroid gland; rather it is a helpful adaptation of the human body to the underlying diseases. We collected 133 hospitalized cases of critical NTI and analyzed the incidence of this phenomenon. Fifty-three per cent of the patients had T3 level lower than 60 ng/dl (normal:85-165 ng/dl) and 60% had T4 level lower than 6 ug/dl (normal:6-12 ug/dl). The lowest levels were observed in patients who had sepsis, were aged over 70 or died in this admission. Free T4 and TSH levels were within normal range in most cases. There is a strong negative correlation between the prognosis and the level of T4 in these patients. Those patients with markedly low levels of T3 and T4 should be treated more sophisticatedly.