Rationale:

• Many diseases can be identified or excluded through laboratory evaluation.

Evidence:

• Sleep studies can quantitate frequency of apneic episodes (241) and indicate the need for continuous positive airway pressure (C-PAP) treatment; weight loss improves sleep apnea (331).
• Blood glucose levels >126 mg/dL on two separate occasions diagnoses diabetes, as does a 2-hour glucose reading of >200 mg/dL (328), or a casual glucose reading of >200 mg/dL with symptoms of diabetes.
• Obesity is associated with more nonalcoholic fatty liver disease that can be diagnosed by ultrasonography in at-risk patients (332).
• Low HDL cholesterol and high triglycerides are consistent with insulin resistance and are criteria for diagnosing the metabolic syndrome (236).
• Low TSH is consistent with hypothyroidism (323).
• Ultrasound of gallbladder can detect gallstones, which are common in obesity (333; 334; 335).
• A 24-hour urinary measure for cortisol is the initial test for diagnosing Cushing's disease to be followed by an overnight dexamethasone suppression test (320).
• High LH/FSH ratio is consistent with polycystic ovary syndrome (321).
• Karyotyping can detect abnormality at 15q11-13 present in Prader-Willi syndrome (325).
• MRI/CT of the brain can detect pituitary or hypothalamic lesions.
• Genotyping can detect melanocortin receptor defect (316), PPAR-γ defects, and leptin and leptin receptor deficiency (129).

Comments:

• None.