Laboratory Testing for Unexplained Weight Gain
For a patient presenting with unexplained weight gain, order a focused panel including: HbA1c (or fasting glucose), lipid panel, TSH, and consider 24-hour urinary free cortisol or late-night salivary cortisol if clinical features suggest Cushing's syndrome. 1, 2
Initial Screening Approach
The key principle is that routine endocrine testing beyond thyroid function is not recommended in obesity unless specific clinical features suggest an underlying endocrine disorder 2. Most endocrine testing should be reserved for cases where history and examination reveal concerning features 2, 3.
Essential Laboratory Tests for All Patients
Order these baseline tests to assess cardiometabolic risk and screen for common obesity-related comorbidities 1:
- HbA1c to screen for diabetes (≥6.5%) and prediabetes (5.7%-6.4%) 1
- Fasting lipid panel including triglycerides, HDL-C, LDL-C, total cholesterol, and non-HDL-C 1
- TSH to screen for hypothyroidism 2, 3
- Liver function tests to evaluate for nonalcoholic fatty liver disease 1
Conditional Testing Based on Clinical Features
Only pursue additional endocrine testing if specific alarm symptoms are present 2, 3:
Screen for Cushing's Syndrome if patient has:
- Rapid weight gain with central obesity
- Facial plethora or moon facies
- Purple striae (>1 cm wide)
- Proximal muscle weakness
- Easy bruising
- Facial edema or hirsutism 3, 4
Testing options for Cushing's syndrome 5, 3:
- 24-hour urinary free cortisol (UFC)
- Late-night salivary cortisol (LNSC)
- Overnight 1 mg dexamethasone suppression test (DST)
Screen for Genetic/Syndromic Obesity if patient has:
- Early-onset obesity (childhood)
- Dysmorphic features or congenital malformations
- Intellectual disability
- Severe hyperphagia
- Strong family history of early obesity 3
Additional Testing for Specific Populations
For women with irregular menses or hirsutism, consider screening for polycystic ovary syndrome 1, 3.
For men with symptoms of hypogonadism (decreased libido, erectile dysfunction), testosterone levels may be warranted 1, 3.
Common Pitfalls to Avoid
- Do not order extensive endocrine panels reflexively - this leads to false positives and unnecessary workup 2
- Do not overlook medication review - psychiatric drugs, corticosteroids, insulin, and certain beta-blockers commonly cause weight gain 3
- Do not forget to assess contributing factors including sleep quality, crash dieting history, smoking cessation, alcohol use, chronic stress, and binge-eating disorder 3
- Remember that lack of height gain with weight gain in children is the hallmark of endocrine causes - this makes detection easier in pediatric populations 5
Risk Stratification Beyond Labs
After obtaining laboratory results, assess for metabolic syndrome (requires 3 of 5 criteria: waist circumference ≥88 cm for women/≥102 cm for men, triglycerides ≥150 mg/dL, fasting glucose ≥100 mg/dL, blood pressure ≥130/85 mm Hg, HDL-C <40 mg/dL in men/<50 mg/dL in women) 1.