Leptin (Greek: thin) is the "satiety" hormone that inhibits hunger and regulates energy levels in the body. It is a specialty test, which may be used along with other tests (thyroid, lipids, insulin, etc) in evaluating the health of obese patients and the underlying conditions. It may also be useful in children classified as obese with a family history of early-onset obesity, or those patients with persistent hunger. While most obese patients have elevated leptin, approx. 10% have some degree of deficiency. Researchers are working to further investigate the role of leptin not only in obesity but also in association with other conditions.