Observations on the Effect of Heparin on Free and Total Thyroxine

Heparin elevates free and total thyroxine in patients with acute myocardial infarction. In 13 patients given heparin as a single bolus the mean free thyroxine rose from 2.4 to 12.4 ng/100 ml (p=0.1 to .001); the mean total thyroxine rose from 7.3 to 8.7 /μg/100 ml (p =0.2 to 0.1). Twelve patients given heparin infusion also demonstrated a rise in free thyroxine but for longer lengths of time. In both groups the rise in free thyroxine was chiefly from a rise in free thyroxine fractions. Acute myocardial infarction, per se, caused no change in free or total thyroxine in 7 patients, nor did warfarin sodium affect these values in 6 patients studied. The demonstration of a rise in total and free thyroxine in 3 athyreotic individuals on replacement therapy with l-thyroxine makes it unlikely that thyroid gland is necessary for this change. It is probable that heparin in some way modifies the thyroxine binding and causes a temporary transfer from its extravascular stores into the intravascular compartmen...