A Study of Thyrotropin Deficiencies by the Combination of Two Tests of TSH Function

ABSTRACT We have found, in normal people, a constant increase in plasma inorganic iodine (PII) after carbimazole or perchlorate administration for 1 day. This increase did not occur in patients with TSH deficiency. Thus, this PII increase test appears to be a reflection of TSH basal activity. Fifty-three hypopituitary patients have been studied by the combination of the PII increase test with the TRH stimulation of TSH release. Thirteen patients had a physiological response to both tests. Fifteen had a complete impairment of TSH secretion with no or a mild response to both tests. Seventeen had an abnormal PII increase test but a rise in plasma TSH after TRH injection. In some of these patients hypothyroidism resulted from pituitary tumors; thus a normal response to releasing hormones does not always mean hypothalamic injury but perhaps a damage to the portal system resulting in a decrease in TRH reaching the pituitary. Nine patients had a normal PII increase test but no or a mild increase in TSH after TRH...