DISTINGUISHING HYPOTHYROXINEMIA DUE TO EUTHYROID SICK SYNDROME FROM PITUITARY INSUFFICIENCY

Patients with severe nonthyroidal illness may have low serum levels of thyroid hormone and thyroid-stimulating hormone (TSH) indistinguishab le from levels in patients with pituitary insufficiency. It is often d ifficult prospectively to rule out pituitary insufficiency in these pa tients. Our hypothesis was that patients sufficiently ill to have low free thyroxine index (FT4I) and TSH from nonthyroidal illness (euthyro id sick syndrome, or ESS) would have serum cortisol levels high enough to make pituitary insufficiency unlikely. Serum samples from all pati ents admitted to the Intensive Care Unit during 2 months were screened for low FT4I, and cortisol levels were measured on those samples. Fiv e of five patients with a diagnosis of ESS had unequivocal elevations of serum cortisol (> 525 nmol/l), arguing against a diagnosis of pitui tary insufficiency. Secondary hypothyroidism due to pituitary insuffic iency can often be ruled out in patients with severe ESS by documentin g appropriate elevated levels of serum cortisol.