Laboratory Testing for Anorexia Nervosa
All patients with suspected or confirmed anorexia nervosa require a complete blood count and comprehensive metabolic panel as core initial laboratory assessment. 1, 2, 3
Essential Initial Laboratory Tests
Complete Blood Count (CBC)
- Order CBC to detect anemia, leukopenia, and thrombocytopenia, which are frequent complications of anorexia nervosa 1, 3, 4
- Anemia occurs in approximately 27% of patients and tends to be normocytic and normochromic 4, 5
- Leukopenia is present in about 36% of patients, manifesting as deficiency of lymphocytes or neutrophils 4, 5
- Thrombocytopenia occurs in approximately 10% of patients and may confer bleeding risk if severe 4, 5
- Pancytopenia is rare (only 3% of patients) but indicates severe bone marrow suppression from malnutrition 5
Comprehensive Metabolic Panel
- Obtain electrolytes (sodium, potassium, chloride, bicarbonate) to identify hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis, particularly in patients with purging behaviors 1, 2, 3, 6
- Measure liver enzymes (transaminases) to detect hepatic dysfunction related to malnutrition 1, 3, 6
- Check renal function tests (BUN, creatinine) to assess kidney function and hydration status 1, 3, 6
- Abnormally low serum albumin levels (≤36 g/L) predict lethal course and should be documented, though albumin is not a reliable marker of nutritional status alone 7
- Monitor for hypoglycemia risk, which can be potentially severe 6
Cardiac Monitoring
- Perform electrocardiogram in all patients with restrictive eating disorders or severe purging behaviors to assess for QTc prolongation and risk of sudden cardiac death 1, 2, 3
- Continue monitoring QTc intervals in patients with ongoing restrictive eating or severe purging 1
Additional Testing Based on Clinical Presentation
Endocrine Evaluation
- Obtain thyroid function tests (TSH, free T4) if oligomenorrhea or amenorrhea is present 8
- Consider hormonal workup to assess for hypothyroidism, hypercorticism, and hypogonadotropic hypogonadism 8, 6
Bone Health Assessment
- Measure 25-hydroxyvitamin D levels if low bone mineral density or bone stress injury is suspected 8
- Consider DXA scan for patients with prolonged amenorrhea due to long-term risk of osteopenia and osteoporosis 8, 7
Micronutrient Assessment
- Check vitamin B12 and folate levels, particularly in patients with small bowel involvement 8
- Consider thiamine levels during refeeding to prevent Wernicke encephalopathy 6
- Monitor for hypophosphatemia, hypomagnesemia, and hypocalcemia during refeeding syndrome 6
Critical Prognostic Indicators
Abnormally low serum albumin (≤36 g/L) and severe weight loss (≤60% of average body weight) at initial examination best predict lethal course, while elevated creatinine and uric acid predict chronic course 7
Important Clinical Caveats
- Normal laboratory values do not exclude serious illness or medical instability - approximately 60% of anorexia nervosa patients show normal values on routine testing even with severe malnutrition 8, 9
- Most laboratory abnormalities are reversible with nutritional rehabilitation and weight restoration 4, 6
- Severe neutropenia (relative risk 15.1) or BMI <12 (relative risk 11.6) significantly increase risk of severe infectious complications 5
- Laboratory assessment must be combined with vital signs (temperature, heart rate, blood pressure, orthostatic changes) and anthropometric measurements (height, weight, BMI) for complete evaluation 1, 3