What baseline metabolic and endocrine laboratory tests should be ordered for an adult patient with obesity when evaluating for secondary medical causes?

Laboratory Evaluation for Obesity to Detect Secondary Medical Causes

All adults with obesity should receive a basic metabolic panel including comprehensive metabolic panel, fasting lipid profile (total cholesterol, LDL, HDL, triglycerides), and thyroid function tests (TSH) as baseline screening. 1 Additional endocrine testing should only be pursued when specific clinical features suggest an underlying endocrine disorder. 2

Core Laboratory Panel (Order for All Patients)

The following tests form the foundation of obesity evaluation and should be obtained routinely:

Metabolic Assessment

• Comprehensive metabolic panel - evaluates kidney function, liver enzymes, and electrolytes 1
• Fasting plasma glucose (≥126 mg/dL indicates diabetes; 100-125 mg/dL indicates prediabetes) 1
• Hemoglobin A1c (≥6.5% indicates diabetes; 5.7-6.4% indicates prediabetes) 1
• Fasting lipid panel including triglycerides, HDL-C, LDL-C, total cholesterol, and non-HDL-C 1

Endocrine Screening

• Thyroid function tests (TSH) - hypothyroidism is highly prevalent in obesity and should be screened universally 1, 2

Liver Assessment

• Liver function tests - to screen for nonalcoholic fatty liver disease/nonalcoholic steatohepatitis 1
• Consider calculating Fibrosis-4 Index if liver enzymes are abnormal 1

Conditional Testing (Only When Clinical Features Present)

Do not perform routine endocrine testing beyond TSH unless specific clinical signs or symptoms suggest an underlying disorder. 2 The European Society of Endocrinology emphasizes that indiscriminate hormonal testing in obesity is not recommended and that weight loss itself often corrects hormonal imbalances. 2

Test for Cushing's Syndrome Only If:

• Thin, atrophic skin with easy bruising 1
• Proximal muscle weakness
• Wide (>1 cm) purple striae
• Rapid weight gain with specific fat distribution (central obesity with thin extremities)

If suspected, order: 24-hour urine free cortisol, late-night salivary cortisol, or 1-mg dexamethasone suppression test 3

Test for Polycystic Ovary Syndrome (PCOS) Only If:

• Hirsutism (excessive facial/body hair) 1
• Acanthosis nigricans (dark, velvety skin in body folds) 1
• Menstrual irregularities
• Infertility

If suspected, order: Total testosterone, free testosterone, DHEA-S, LH, FSH 1

Test for Male Hypogonadism Only If:

• Decreased libido
• Erectile dysfunction
• Loss of muscle mass
• Gynecomastia

If suspected, order: Morning total testosterone, free testosterone 1, 3

Test for Growth Hormone Deficiency Only If:

• History of pituitary disease or cranial irradiation
• Other pituitary hormone deficiencies present
• Severe fatigue with decreased muscle mass

If suspected, order: IGF-1 level 3

Important Clinical Pitfalls

Obesity itself causes hormonal changes that can mimic endocrine disease. 4, 2 For example:

• T3 is often elevated in obesity without thyroid disease 4
• Growth hormone is typically low in obesity but does not indicate GH deficiency 4
• Cortisol responses to stimulation tests may be exaggerated in central obesity 4
• Total testosterone is low in obese men due to decreased SHBG, but free testosterone is usually normal 4

The most critical distinction: These obesity-related hormonal changes typically normalize with weight loss and do not require hormonal replacement therapy. 2 Therefore, extensive endocrine testing without specific clinical features wastes resources and may lead to inappropriate treatment.

Screening for Obesity-Related Comorbidities

Beyond evaluating for secondary causes, assess for complications:

• Blood pressure measurement - hypertension defined as ≥130/80 mmHg 1
• Metabolic syndrome criteria - requires 3 of: waist circumference ≥88 cm (women) or ≥102 cm (men), triglycerides ≥150 mg/dL, fasting glucose ≥100 mg/dL, blood pressure ≥130/85 mmHg, HDL-C <40 mg/dL (men) or <50 mg/dL (women) 1
• Clinical screening for obstructive sleep apnea using STOP-BANG questionnaire or Epworth Sleepiness Scale, with polysomnography if positive 1

Special Populations

For patients with early-onset obesity, hyperphagia, developmental delay, or dysmorphic features: Consider genetic/syndromic obesity and refer to specialized obesity medicine or genetics clinic. 3 Standard laboratory panels are insufficient for these presentations.

For patients age 40-70 years: The U.S. Preventive Services Task Force specifically recommends screening for abnormal blood glucose as part of cardiovascular risk assessment. 1