Low antithrombin III in morbid obesity: return to normal with weight reduction

Morbidly obese adults are at increased risk for perioperative thrombotic complications. Antithrombin III (AT III) is a major endogenous anticoagulant and its deficiency is associated with more frequent thrombotic diseases. We measured AT III quantity and function in 23 morbidly obese adults and in 19 otherwise identical people who had reduced their mean weight to 160% of ideal body weight. Both groups were compared to normal weight controls (less than 120% ideal body weight). Serum and plasma AT III function and serum AT III antigenic concentration were significantly lower in the morbidly obese people compared to the weight reduced group in all three assays. The reduced group had values within the normal range of the normal weight group. In addition, three patients studied both before and after weight loss had similar significant changes in their AT III. We conclude that AT III is reduced in morbidly obese adults and normalizes as weight is reduced. Possible mechanisms of this deficiency and therapeutic approaches are considered.