Prevalence of iatrogenic hyperthyroidism in a community hospital

There is wide agreement that thyroid hormone replacement should not be given in doses sufficient to suppress thyroid-stimulating hormone (TSH). The purpose of our study was to determine the prevalence of patients currently taking levothyroxine who have an inappropriately suppressed TSH and are thereby at risk for complications of overt or subclinical hyperthyroidism. Those complications of particular concern are osteoporosis and cardiac toxicity, specifically atrial dysrhythmias and development of left ventricular hypertrophy.

The charts of all 1652 patients dispensed levothyroxine in 1994 from an Air Force community hospital were selected for review. Of these, 905 patients had an available TSH measurement for the same calendar year, and their status was evaluated further.

Of 905 patients, 110 (12.2 percent) had TSH levels of less than 0.1 microU/mL; 63 (7 percent) had no indication for suppression, and 21 (2.5 percent) were overtly thyrotoxic. The odds ratio for inappropriate suppression in women was 2.83 (95 percent CI 1.05 - 7.68).

The frequent use of levothyroxine suggests that TSH suppression could represent a serious public health concern, particularly for postmenopausal women and patients with heart disease.