What labs should be ordered for a patient presenting with weight gain?

Laboratory Tests for Patients Presenting with Weight Gain

For patients presenting with weight gain, a comprehensive laboratory evaluation should include a complete metabolic panel, fasting lipid profile, thyroid function tests, and screening for abnormal blood glucose as the essential initial tests. 1

Initial Laboratory Assessment

• Complete blood count (CBC) to evaluate for underlying conditions that may contribute to weight gain 1
• Comprehensive metabolic panel to assess liver function, kidney function, and electrolytes 1
• Fasting lipid profile including total cholesterol, LDL, HDL, and triglycerides 1
• Thyroid function tests (TSH, free T4, free T3) to rule out hypothyroidism, which can cause weight gain 1, 2
• Fasting blood glucose or hemoglobin A1c to screen for diabetes or prediabetes 1

Additional Tests Based on Clinical Suspicion

• Overnight dexamethasone suppression test if Cushing's syndrome is suspected (central obesity, "moon face," violaceous striae) 1
• Urinary free cortisol for further evaluation of suspected Cushing's syndrome 1
• Plasma aldosterone/renin ratio if hypertension is present with unexplained weight gain 1
• Serum insulin levels to evaluate for insulin resistance, which is associated with weight gain and may correlate with thyroid function 3, 4

Screening for Sleep Disorders

• Sleep studies (polysomnography) should be considered for patients with symptoms of obstructive sleep apnea (snoring, daytime sleepiness, witnessed apneas), which is common in patients with obesity 1
• Berlin Questionnaire or Epworth Sleepiness Scale can be used as screening tools before proceeding to formal sleep studies 1

Specialized Testing for Secondary Causes

• 24-hour urinary fractionated metanephrines if pheochromocytoma is suspected (paroxysmal hypertension, headaches, palpitations) 1
• Serum calcium and parathyroid hormone levels if hyperparathyroidism is suspected 1
• Liver function tests to evaluate for nonalcoholic fatty liver disease (NAFLD), which is common in patients with obesity 1

Considerations for Special Populations

• For patients with eating disorders: In addition to the above tests, an electrocardiogram should be performed, especially for patients with restrictive eating patterns or severe purging behaviors 1
• For patients with bipolar disorder on medications: Regular monitoring of weight and metabolic parameters is essential as many psychotropic medications can cause weight gain 1
• For diabetic patients: Additional testing should include urinary albumin-to-creatinine ratio and vitamin B12 levels (if on metformin) 1

Interpreting Results in Context

• Thyroid function may show subtle changes in obese patients, with TSH often being slightly higher and free T3 lower compared to non-obese individuals, even within the normal range 2, 4
• Insulin resistance (measured by HOMA-IR) may correlate with TSH levels in obese patients 3, 4
• Lipid abnormalities are common in patients with weight gain and should be interpreted in the context of other metabolic parameters 1, 3

Common Pitfalls to Avoid

• Failing to consider medication-induced weight gain - always review current medications that may contribute to weight gain 1
• Not screening for endocrine disorders in patients with rapid or unexplained weight gain 1
• Overlooking the possibility of fluid retention versus true adipose tissue gain, which require different diagnostic approaches 1
• Neglecting to evaluate for psychological factors such as depression or binge eating disorder, which can contribute to weight gain 1

Remember that laboratory testing should be guided by the patient's clinical presentation, and results should be interpreted in the context of a complete history and physical examination to determine the underlying cause of weight gain 1.