Laboratory Evaluation for Weight Gain
Order a comprehensive metabolic panel, fasting lipid profile, thyroid function tests (TSH, free T4), and fasting blood glucose or hemoglobin A1c as your essential initial workup for any patient presenting with weight gain. 1, 2
Core Initial Laboratory Tests
The following tests form the foundation of your evaluation and should be ordered for every patient with weight gain:
Comprehensive metabolic panel to assess liver function (ALT, AST, alkaline phosphatase), kidney function (creatinine, BUN), and electrolytes (sodium, potassium, chloride, bicarbonate) 1, 2
Fasting lipid profile including total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides to evaluate cardiovascular risk and metabolic abnormalities 1, 2
Thyroid function tests including TSH, free T4, and free T3 to rule out hypothyroidism, which commonly causes weight gain 1, 2
Fasting blood glucose or hemoglobin A1c to screen for diabetes or prediabetes 1, 2
Complete blood count (CBC) to evaluate for underlying conditions that may contribute to weight gain 1, 2
Additional Tests Based on Clinical Presentation
Order these tests only when specific clinical features suggest an underlying endocrine or metabolic disorder:
For Suspected Cushing's Syndrome
Look for central obesity, "moon face," violaceous striae, proximal muscle weakness, or easy bruising:
- Overnight dexamethasone suppression test (1 mg at 11 PM, measure cortisol at 8 AM) 1, 2
- 24-hour urinary free cortisol for confirmation 1, 2
For Hypertension with Unexplained Weight Gain
For Suspected Pheochromocytoma
Look for paroxysmal hypertension, headaches, palpitations, or diaphoresis:
For Suspected Hyperparathyroidism
Look for kidney stones, bone pain, or unexplained hypercalcemia:
Screening for Associated Conditions
Sleep Disorders
Consider polysomnography if the patient has snoring, daytime sleepiness, or witnessed apneas, as obstructive sleep apnea is common in obesity 1
- Use the Berlin Questionnaire or Epworth Sleepiness Scale as screening tools before ordering formal sleep studies 1
Nonalcoholic Fatty Liver Disease
- Liver function tests (ALT, AST) should be evaluated, as NAFLD is common in patients with obesity 1
- Note that elevated gamma-glutamyl transferase (GGT) may indicate increased cardiovascular risk in metabolic syndrome 3
Special Population Considerations
Medication-Induced Weight Gain
Review all current medications, as many drugs cause weight gain including antipsychotics, mood stabilizers, antidepressants, corticosteroids, and certain antihypertensives 1, 2
Patients with Diabetes
- Urinary albumin-to-creatinine ratio to screen for diabetic nephropathy 1
- Vitamin B12 levels if the patient is taking metformin 1
Patients with Eating Disorders
- Electrocardiogram especially for those with restrictive eating patterns or severe purging behaviors 1
Patients with Bipolar Disorder
- Regular monitoring of weight and metabolic parameters is essential for those on weight-promoting medications 1, 2
Monitoring Strategy
Document weight and BMI at baseline and every 6 months to identify excessive weight gain, particularly in patients starting medications known to cause weight gain 2
- Monitor blood pressure at each clinical visit to diagnose incident hypertension 2
- Use the Edmonton Obesity Staging System (EOSS) to classify disease severity based on obesity-associated risk factors, complications, mental health, and functional limitations 2
Common Pitfalls to Avoid
Do not attribute hypoalbuminemia solely to malnutrition in hospitalized patients, as it is most commonly low as part of an acute phase response to inflammation 4
Interpret laboratory abnormalities in clinical context, as some findings may be a consequence rather than cause of obesity 5
Weight measurements may be unreliable in severe illness due to fluid retention and edema; assess fluid intake and output alongside weight changes 4
Screen for psychological factors such as depression or binge eating disorder, which can contribute to weight gain 1