Causes of high free-thyroxine index values in sick euthyroid elderly patients.

Modest elevation of the free-thyroxine index occurs in many apparently euthyroid elderly in-patients. The present study investigated the possible relevance of drug side-effects to this problem. It appears that such side-effects associated with the use of L-Dopa, digoxin and co-trimoxazole account for a substantial proportion of the observed elevated free-thyroxine index results.