Laboratory Tests for Patients with Eating Disorders
The laboratory assessment of a patient with a possible eating disorder should include a complete blood count (CBC) and a comprehensive metabolic panel, including electrolytes, liver enzymes, and renal function tests. 1 Additionally, an electrocardiogram (ECG) is recommended for patients with restrictive eating disorders, severe purging behaviors, or those taking medications known to prolong QTc intervals.
Core Laboratory Testing
Essential Tests:
- Complete Blood Count (CBC) 1, 2
- Comprehensive Metabolic Panel 1, 2 including:
- Electrolytes (sodium, potassium, chloride, bicarbonate)
- Liver enzymes
- Renal function tests (BUN, creatinine)
- Glucose
- Electrocardiogram (ECG) for patients with 1:
- Restrictive eating disorders
- Severe purging behaviors
- Patients on medications that prolong QTc intervals
Additional Important Tests:
- Magnesium and phosphate levels 3 - particularly important in severely malnourished patients at risk for refeeding syndrome
- Thyroid function tests - to rule out thyroid disorders that may mimic eating disorder symptoms
Testing Based on Clinical Presentation
For Patients with Purging Behaviors:
- Serum electrolytes with special attention to:
- Potassium (hypokalemia)
- Chloride and bicarbonate (metabolic alkalosis)
- Amylase (may be elevated with frequent vomiting)
For Severely Malnourished Patients:
- Calcium levels
- Phosphorus (critical for monitoring refeeding syndrome)
- Magnesium
- Albumin (marker of nutritional status)
Monitoring Frequency
Laboratory monitoring should be tailored to the severity of the eating disorder:
- Severe malnutrition (BMI < 15 kg/m²): Weekly monitoring of electrolytes, especially during initial refeeding
- Moderate malnutrition: Every 2-4 weeks during active treatment
- Mild cases or maintenance phase: Monthly to quarterly
Important Caveats
Normal laboratory values do not exclude serious eating disorders 4. Up to 60% of patients with eating disorders may have normal laboratory values despite significant malnutrition.
Laboratory abnormalities correlate with BMI 4 - patients with BMI below 14.5 kg/m² are more likely to show abnormalities, but even severely malnourished patients may have normal labs.
ECG findings may reveal bradycardia, prolonged QTc interval, or other arrhythmias that require immediate intervention, even when laboratory tests are normal.
Orthostatic vital signs should be checked alongside laboratory tests, as they may indicate cardiovascular compromise before lab abnormalities appear.
Interpretation and Action
- Electrolyte abnormalities (particularly hypokalemia, hyponatremia, or hypophosphatemia) may require immediate hospitalization and correction
- Bradycardia (heart rate < 40 bpm) or prolonged QTc (> 450 ms) on ECG warrant urgent cardiac evaluation
- Leukopenia or thrombocytopenia on CBC may indicate severe malnutrition requiring more aggressive nutritional rehabilitation
Laboratory testing is an essential component of eating disorder assessment but should always be interpreted in the context of the patient's clinical presentation, including vital signs, physical examination findings, and psychological symptoms.