Please note: Eating disorders develop in men, women, girls, and boys. For ease in reading, we have used "she" and "her" in the text below.

Laboratory work, in conjunction with a comprehensive history and physical exam, helps determine whether a patient has an eating disorder and/or another illness that can manifest as unexpected weight loss, such as diabetes mellitus, inflammatory bowel disease, cancer or thyroid problems. Some individuals have an eating disorder along with one of these other conditions. Although there is no one test that definitively points to an eating disorder, laboratory data can provide clues to the illness and to how far it has progressed.

It is important to understand that routine studies—CBC (complete blood count), erythrocyte sedimentation rate (ESR), chemistry panel and urinalysis—are often normal, especially if the patient is early in the disease process.

Anemia and/or leukopenia (low white blood cell count) and/or thrombocytopenia (reduced platelet count) can occur in anorexia nervosa because semi-starvation tends to impede the bone marrow’s ability to generate new blood cells. White blood cells play an important role in the body’s immune system. Interestingly, leukopenia in anorexia nervosa does not seem to increase vulnerability to infection; however, an infection that does develop may require extra time to heal. Bone marrow suppression is particularly likely in the context of severe weight loss, but with nutritional restoration hematology results usually return to normal.

Another major concern involves fluids and electrolytes. Some patients drink excessive volumes of water prior to weigh-ins in an attempt to create the impression that they have adhered to their prescribed nutrition programs when they really haven’t. Too much water can lead to hyponatremia (low serum sodium level) which increases vulnerability to seizures. In order to detect water-loading, primary care physicians will often test a patient’s urine for specific gravity.

Semi-starvation dips into the body’s supply of phosphorus, a mineral that helps cells produce energy and proteins. Serum phosphorus levels in patients with anorexia nervosa are typically normal when initially tested but may drop when nutritional replenishment begins. Unless treated, phosphorus depletion can contribute to “re-feeding syndrome” which has a potentially adverse effect on the heart, lungs, kidneys and other organs.

Hypokalemia (low serum potassium) can lead to serious cardiac arrhythmias and must be corrected. Potassium loss often accompanies dehydration and is more likely to occur in individuals who induce vomiting or misuse laxatives or diuretics than in those who do not engage in these behaviors. As worrisome as it is to find electrolyte disturbances in those who are undernourished, normal-weight patients who purge frequently are also at risk. This is one important reason medical monitoring is necessary for patients with bulimia nervosa. As an individual works in treatment to reduce her abnormal eating behaviors, her electrolyte balance is likely to improve.

Other potential lab findings include abnormal liver function tests which can occur with starvation or early nutritional restoration, or be unrelated to the patient’s eating disorder. Hypoglycemia may be present in anorexia nervosa and thyroid function tests are sometimes abnormal secondary to undernutrition. Elevated serum cholesterol and/or normal-high LDL levels are occasionally found in anorexia nervosa even though patients with this disorder ingest negligible amounts of cholesterol and fat.

The electrocardiograms of most individuals with anorexia nervosa demonstrate sinus bradycardia, and reduced R-wave amplitude in V6 is also common.

Low body fat, low weight, undernutrition, excess physical activity and emotional stress disrupt the functioning of the body’s reproductive hormones, causing menstrual periods to stop or become irregular. Amenorrhea (absent menses), a well-known feature of anorexia nervosa, leads to low levels of estradiol (estrogen). Males with anorexia nervosa manifest low levels of testosterone.

Amenorrhea and low estrogen levels can result in bone loss (osteopenia) and the more serious osteoporosis, which leaves bones weak, fragile and prone to fracture. As compared to normal bones, those suffering from osteoporosis are less dense in structure.

    Skeletal Architecture in Healthy Young Woman






    Skeletal Architecture in Young Woman with Anorexia Nervosa

Anorexia nervosa also has an effect on the brain. CT (computed tomography) and MRI (magnetic resonance imagery) studies of patients with this illness demonstrate reduction in gray matter (cell bodies of neurons) and white matter (filaments that transmit messages between neurons), and these changes resolve partially with nutritional restoration.