Doctors look for such common signs of anorexia as a patient's conviction that she needs to lose weight, a weight loss of at least 25 percent, and absence of at least 3 consecutive menstrual periods. The physician must also rule out other medical problems that could be responsible for the weight loss.

There is no laboratory test for anorexia, although your doctor may draw blood to check for physical problems such as anemia. Since several other physical diseases and mental disorders cause many of the same physical problems, your physician will rely mainly on your attitude toward eating and information about your behavior in making a diagnosis.