Laboratory Tests for Individuals Having Difficulty Losing Weight
For individuals struggling with weight loss, a comprehensive laboratory evaluation should include screening for prediabetes/diabetes, thyroid disorders, and other metabolic conditions that may contribute to weight management difficulties. 1
Initial Laboratory Evaluation
- Fasting plasma glucose (FPG), 2-hour plasma glucose during 75-g oral glucose tolerance test (OGTT), and/or hemoglobin A1C should be ordered to screen for prediabetes and diabetes, as these conditions can contribute to weight management difficulties 1
- Thyroid function tests (TSH and free T4) are essential to rule out hypothyroidism, which can cause weight gain or difficulty losing weight 1, 2
- Comprehensive metabolic panel including electrolytes, liver function tests, and kidney function tests to assess overall metabolic health 1, 3
- Lipid profile including HDL cholesterol, LDL cholesterol, and triglycerides to evaluate cardiovascular risk and metabolic syndrome 1
Additional Testing Based on Clinical Presentation
- Complete blood count (CBC) to assess for anemia or other hematologic abnormalities that may contribute to fatigue and reduced physical activity 3
- Vitamin D levels should be checked as deficiency is common in obesity and may affect metabolism 3
- Iron studies including serum ferritin and transferrin saturation to evaluate iron status, particularly in women of reproductive age 3
- Sex hormone levels should be considered in women with signs of polycystic ovary syndrome (PCOS) such as hirsutism, irregular periods, or acanthosis nigricans 1
Special Considerations
Testing for prediabetes and type 2 diabetes should be prioritized in individuals with BMI ≥25 kg/m² (or ≥23 kg/m² in Asian Americans) who have additional risk factors such as:
- First-degree relative with diabetes 1
- High-risk race/ethnicity (e.g., African American, Latino, Native American, Asian American) 1
- History of cardiovascular disease 1
- Hypertension (≥130/80 mmHg or on therapy for hypertension) 1
- HDL cholesterol <35 mg/dL and/or triglycerides >250 mg/dL 1
- Polycystic ovary syndrome 1
- Physical inactivity 1
- Acanthosis nigricans or other conditions associated with insulin resistance 1
For patients with signs of central obesity, waist circumference measurement is important as it has been associated with alterations in thyroid function independent of BMI 4
Monitoring and Follow-up
- If initial tests are normal but weight loss difficulties persist, repeat testing at minimum 3-year intervals is recommended 1
- For patients with prediabetes (A1C 5.7-6.4%, impaired fasting glucose, or impaired glucose tolerance), yearly testing is recommended 1
- Consider more frequent testing if risk factors change or symptoms develop 1
Pitfalls and Considerations
- Thyroid function test interpretation can be challenging in obesity, as TSH and free T3 levels may be slightly elevated even in euthyroid obese individuals 5, 4
- Weight loss itself can affect thyroid hormone levels, with potential decreases in T3 during caloric restriction, particularly with high-protein, low-carbohydrate diets 6
- Laboratory abnormalities should be interpreted in clinical context, as some findings may be a consequence rather than cause of obesity 1, 4
- Medication review is essential as many medications can contribute to weight gain and should be identified during evaluation 1
Remember that laboratory testing is just one component of a comprehensive evaluation for weight management difficulties, which should also include assessment of dietary habits, physical activity levels, sleep patterns, and psychological factors 1.