In terms of obesity diagnosis, the history, physical examination, and laboratory evaluation of overweight and obese patients are directed toward three goals: first, to identify secondary causes of obesity; second, to identify comorbid conditions; and third, to establish the patient’s dietary and activity habits.

Height and weight measurements in the office are used to classify patients as overweight or obese according to BMI criteria; however, these criteria may not apply to patients who have gained weight as the result of increased muscle mass from intensive exercise.

Evaluation of abdominal obesity requires the use of a tape measure. A waist circumference (obtained at the level of the superior iliac crest) greater than 40 inches (102 cm) in a man or greater than 35 inches (88 cm) in a woman is considered abnormal.

Specific physical findings that might indicate secondary causes of obesity include pretibial edema and delayed tendon reflexes (hypothyroidism), purple striae, supraclavicular fat pad enlargement, and muscle weakness (Cushing syndrome). Other aspects of the clinical evaluation focus on comorbid conditions.

A number of the symptoms associated with diseases that can cause or contribute to unwanted weight gain, such as hypothyroidism or Cushing disease, occur frequently in overweight patients. These include fatigue, aches, cold intolerance, constipation, poor exercise tolerance, central obesity, loss of libido, and depression. Deciding when to screen a patient for secondary causes of obesity, therefore, can be a challenge for the practitioner.

Establishing a pattern of weight gain may be helpful. A patient with a lifelong history of being heavy and a stable adult weight is unlikely to have a secondary cause of obesity. A sudden or rapid weight gain over a few months or years, however, especially when accompanied by onset of comorbid conditions, may correspond to the prescription of medications that contribute to excess weight gain (especially steroids and newer antipsychotics) or indicate onset of an illness that requires further evaluation.

The history should include questions about diseases for which overweight and obese patients are at higher risk, including hypertension, impaired glucose tolerance or diabetes, hyperlipidemia, heart disease, pulmonary disease, and sleep apnea. These conditions may cause minimal or no symptoms, and therefore may be present for months or years before a diagnosis is made. Sleep apnea in particular is a common cause of fatigue and poor concentration or work performance in obese patients; these symptoms are often mistakenly ascribed to an abnormally functioning thyroid gland (despite normal results on thyroid function tests) or a so-called altered metabolism. This diagnosis may be missed unless the clinician specifically asks about characteristic symptoms: restless sleep at night, snoring or observed apnea, fatigue or headache upon awakening and during the daytime, and spontaneous daytime sleep when inactive or while driving.

In severely obese patients, increasing peripheral edema, orthopnea, and worsening exercise tolerance may be symptoms of congestive heart failure or pulmonary hypertension and right-sided heart failure from severe sleep apnea. New-onset headaches may indicate normal-pressure hydrocephalus. Gastroesophageal reflux disease usually results in heartburn or an acid taste in the throat. During a period of weight gain, women may develop irregular periods or symptoms of androgen excess. Although commonly diagnosed as polycystic ovary syndrome (PCOS), these findings differ from classic PCOS in that they occur after menarche and are not usually associated with polycystic ovaries.

Finally, inquiring about past and present dietary and activity habits is important for subsequent discussions of medical and surgical management. Most overweight and obese patients will have made numerous attempts to lose weight, through diets, exercise regimens, or commercial weight-loss programs. Because of unrealistic expectations and the inevitable weight regain that occurs, patients are often discouraged or leery of new advice.