What is being tested?
Leptin is a hormone that helps regulate appetite by signaling hunger satisfaction (satiety). This test measures the amount of leptin in the blood to detect a deficiency that may be contributing to obesity.
Leptin is produced primarily by fat cells (adipocytes) and to a lesser degree by other tissues, including the placenta in pregnant women. It is transported in the blood receptors in the hypothalamus in the brain. When sufficient food has been consumed, it tells the body that it is no longer hungry. In a normal feedback response, a low level of leptin triggers hunger and an increase in food consumption. As the level of leptin rises from an increase in fat cells, hunger diminishes and food consumption drops off.
Insufficient leptin can cause persistent hunger as the body attempts to protect itself from perceived underfeeding (starvation). Very rare inherited leptin deficiencies can cause severe obesity through constant hunger and constant eating that starts in early childhood. Leptin replacement therapy has been shown to be successful in treating some of those affected.
Obesity is most commonly associated with elevated leptin levels. This is thought to be due to a resistance to leptin that is similar to the insulin resistance often seen with obesity. People who are affected are resistant to the action of leptin—they continue to experience hunger even after consuming sufficient food. The body continues to produce more leptin in an attempt to compensate and in response to the perceived hunger. However, about 10% of those who are obese are estimated to have some degree of leptin deficiency.
There is significant interest in better understanding leptin’s ties to obesity. Obesity is a major health concern in the U.S. because it increases the risk of many conditions, such as high blood pressure (hypertension), dyslipidemias (high cholesterol and/or high triglycerides), type 2 diabetes, joint problems, sleep apnea, coronary heart disease, stroke, and some cancers. The rate of obesity has increased steadily over the last 20 years in all age ranges and, according to the Centers for Disease Control and Prevention, more than one-third of adults and 17% of children and teens in this country are currently classified as obese. Classification is based on body mass index or BMI. (See Common Questions below).
A recent study found that in some people a leptin level might be more accurate than the traditional body mass index in gauging how much excess fat a person is carrying. In general, the higher the level of leptin in the bloodstream, the more fat tissue a person has. In the study, this was especially true with older women and in those with large muscles or dense bones where the results of the BMI score could be misleading.
Research is ongoing to evaluate leptin’s roles in the body and the links between leptin and obesity, and between leptin and successful weight loss. There is also continued interest in determining whether a leptin-based treatment might be useful for those who are obese and leptin-deficient.
How is it used?
The leptin test is not ordered routinely and its usefulness in medical settings is yet to be fully established. Most testing is still performed in a research setting as the role of leptin is further investigated.
In clinical settings, the leptin test is most likely to be ordered on an obese child, especially if there is a family history of early-onset obesity. It may sometimes be ordered on an obese person who has symptoms of frequent, persistent hunger to detect a leptin deficiency or excess.
On occasion, the test may be used along with other tests, such as a lipid profile, thyroid panel, glucose, insulin, and/or A1c, to evaluate the health status of an obese person and to detect underlying conditions that may be contributing to or complicating their condition.
When is it ordered?
Leptin is primarily ordered during clinical studies, when it is performed to further investigate the role of leptin.
Leptin testing is not frequently ordered outside of a research setting, but it may sometimes be ordered when a child has been classified as obese, especially when there is a family history of early-onset obesity. (For classifications, see Common Questions below.)
Some doctors may order a leptin test when evaluating an obese person to determine whether they may have a leptin deficiency or an excess (to detect leptin resistance).
What does the test result mean?
In the obese, decreased leptin levels may indicate some degree of deficiency, while increased concentrations are thought to be associated with resistance to the effects of leptin. Most obese people will have increased levels, but about 10% may have some degree of leptin deficiency.
Very rarely, significantly decreased leptin levels may indicate an inherited leptin deficiency linked to severe obesity.
Leptin secretion follows a circadian pattern, meaning that the concentration in blood will vary throughout a 24-hour time period (higher at night than during the day).
Is there anything else I should know?
Women normally have higher leptin levels than men. Leptin concentrations are also increased during pregnancy and may be significantly increased in women with gestational diabetes or preeclampsia. The test is not, however, used to monitor these conditions.
The usefulness of leptin results in a medical setting, especially in evaluating excess or and deficient amounts of the hormone, is yet to be fully established. For instance, someone with a rare inherited deficiency may benefit from leptin replacement therapy, but there is not yet sufficient data to determine whether or not a person with a mild deficiency would also benefit from a targeted treatment.
Some of the other topics that have been or are being studied in association with leptin include its:
- Contribution to inflammation and atherosclerosis or, conversely, its protection from atherosclerosis
- Increase with gestational diabetes and with pre-eclampsia during pregnancy
- Role in fertility
- Association with depression, stress, and anxiety
- Role in maintaining glucose levels and its interaction with insulin
- Association between leptin levels, weight loss, and hunger
Should everyone who is overweight have a leptin test performed?
Leptin testing is not routinely performed and is not indicated for most people. If someone is obese and has persistent hunger, or has a young child who is severely obese, then leptin testing may be considered.
How are classifications of body weight determined?
Classification is currently based on body mass index, or BMI.
For youth, weight and height as well as age and sex are considered in determining their BMI percentile. An overweight youth is one whose BMI is between the 85th percentile and the 94th percentile on standardized growth charts. An obese youth is one who is at or above the 95th percentile on standardized growth charts or has a BMI of greater than or equal to 30 kg/m2, whichever is lower.
For adults, BMI is calculated as:
BMI = (Weight in pounds) / (height in inches squared) x 703
Less than 18.5 Underweight
18.5 – 24.9 Normal weight
25.0 – 29.9 Overweight
30 and above Obese
Can leptin testing be performed in my doctor's office?
No. Leptin testing is not performed in doctors’ offices and is not offered by most laboratories. The test will probably need to be sent to a reference laboratory.
What can I do to lower or increase leptin levels?
Leptin levels will often decrease when an obese person loses weight and increase when a person becomes obese, but they do not otherwise respond to lifestyle changes.
How is leptin deficiency treated?
In those with very rare inherited leptin deficiencies, replacement therapy has been successful in addressing obesity. However, there are insufficient data at this time to support its routine use for other leptin deficiencies.
Are there other adipokines besides leptin?
Although leptin was the first adipocyte cytokine (or “adipokine”) identified, many others have been discovered. The two that have been most extensively investigated are resistin, which increases insulin resistance, and adiponectin, which lowers it. Resistin is increased and adiponectin is decreased in obesity. They also have opposite effects on inflammation; resistin increases inflammation, while adiponectin decreases it. Another recently discovered adipokine is visfatin, which is elevated in type 2 diabetes and may play a role in elevating insulin levels. Several other adipokines are aplin, chemerin, and omentin, all of which appear to be anti-inflammatory.