Medication and low serum thyroxine values in nursing home residents

The nursing home clinician may encounter euthyroid residents with low total serum thyroxine (T4) values associated with certain medications or nonthyroidal illness (NTI). Hypothyroidism may be incorrectly diagnosed and thyroid hormone prescribed.

We reviewed all T4 determinations and individuals with low T4 and normal thyroid-stimulating hormone (TSH) levels were identified. Pharmacy and medical records were reviewed.

We reviewed 1,153 T4 determinations and identified 22 individuals with low T4 and normal TSH values. Eight of the 22 (36%) were being treated with high-dose salicylates, 4 (18%) with phenytoin, 3 (14%) with carbamazepine, and 2 (9%) with prednisone (15 mg/day). Three residents were on two of these medications. None was on prednisone as a single medication. Eight were on none of the medications, and 5 of these had albumin values of < or = 3.2 g/dL (a marker of NTI). After a low T4 value was determined in these individuals, 6 of the 22 were placed on T4 replacement with no documentation of hypothyroidism. In 5 of these, low T4 level could be attributed to a medication effect.

Low total T4 with normal TSH levels are commonly associated with medications and NTI.