THE EFFECTS OF SERIOUS ILLNESS AND SURGICAL STRESS ON THE CIRCULATING THYROID HORMONE*

Abstract

NOT infrequently it is necessary to evaluate the functional state of the thyroid of critically ill patients. Appraisal on clinical grounds alone may be difficult in patients suffering from associated diseases, and since the basal metabolic rate may be unreliable under these circumstances, appraisal of thyroid function by determination of the serum precipitable iodine (SPI) concentration is frequently employed. Consequently, it is necessary to know with certainty whether or not serious illness, acute or chronic, will influence the level of the circulating thyroid hormone in man. Studies in experimental animals have suggested that environmental stress (such as exposure to cold, violent exercise, injections of formalin) may alter thyroid function by depressing the rate of thyroidal uptake of radioiodine (1, 2, 3) and may also increase the rate of peripheral utilization of thyroid hormone (4). These combined effects should have a tendency to lower the concentration of circulating thyroid hormone. Furthermore, the adrenocortical hormones, which are known to increase during stress, have been reported to depress the iodine-accumulating function of the thyroid in animals without altering the rate of release of hormone from the gland (5, 6).