Laboratory Evaluation for Weight Loss
Basic laboratory evaluation for weight loss should include a comprehensive metabolic panel, fasting lipid profile, and thyroid function tests 1. This foundational approach screens for both secondary causes of weight changes and obesity-related metabolic complications.
Core Laboratory Tests
The essential initial workup consists of:
- Comprehensive metabolic panel (CMP) - evaluates glucose metabolism, liver function, kidney function, and electrolytes 1
- Fasting lipid profile - assesses for dyslipidemia including elevated triglycerides, low HDL-C, and elevated LDL-C 1
- Thyroid function tests (TSH) - screens for thyroid disorders as a secondary cause of weight changes 1, 2
- Hemoglobin A1C - particularly important for screening abnormal glucose metabolism in adults aged 40-70 years with overweight or obesity 1
Additional Testing Based on Clinical Context
Beyond the basic panel, targeted testing should be guided by history and physical examination findings:
- Complete blood count (CBC) - evaluates for anemia and other hematologic abnormalities 1, 2
- Liver function tests - specifically alanine aminotransferase (ALT) to screen for non-alcoholic fatty liver disease, though normal ALT does not exclude hepatic steatosis 1
- Fasting glucose or glucose tolerance testing - when diabetes screening is indicated based on cardiovascular risk assessment 1
Physical Examination Findings That Guide Additional Testing
The physical exam should specifically assess for:
- Acanthosis nigricans - suggests insulin resistance, warranting glucose and insulin testing 1
- Hirsutism - associated with polycystic ovarian syndrome, may require hormonal evaluation 1
- Large neck circumference - associated with obstructive sleep apnea, consider sleep studies 1
- Thin, atrophic skin - suggests Cushing's disease, requiring cortisol evaluation 1
Important Clinical Caveats
Weight loss itself does not differentiate between fat mass and lean mass loss 1. In longitudinal studies, lean mass accounted for 40-60% of weight lost in some cohorts 1. This is particularly relevant in older adults who experience 1% skeletal muscle mass decline annually 1.
Normal liver enzymes do not exclude fatty liver disease - up to 80% of subjects with increased intrahepatic triglyceride content have normal ALT concentrations 1. More sophisticated imaging may be needed if clinical suspicion is high.
The U.S. Preventive Services Task Force specifically recommends screening for abnormal blood glucose as part of cardiovascular risk assessment in the 40-70 year age group with overweight or obesity 1.
Screening for Obesity-Related Comorbidities
Beyond identifying causes of weight changes, laboratory testing should screen for:
- Metabolic syndrome components - including prediabetes (impaired fasting glucose), dyslipidemia, and markers of cardiovascular disease risk 1
- Type 2 diabetes - using fasting glucose, A1C, or glucose tolerance testing 1
- Cardiovascular risk factors - comprehensive lipid panel and glucose metabolism assessment 1
An ECG should be obtained to check for evidence of coronary heart disease and establish a baseline for future comparisons 1.