Laboratory Assessment for a 14-Year-Old with Eating Disorder
Draw a complete blood count and comprehensive metabolic panel (including electrolytes, liver enzymes, and renal function tests) as your core initial laboratory assessment, and obtain an electrocardiogram if there is restrictive eating, severe purging, or use of QTc-prolonging medications. 1, 2
Core Laboratory Tests (Essential for All Patients)
Complete Blood Count
- Order a CBC to assess for anemia, leukopenia, and other hematologic abnormalities that commonly occur with malnutrition 1, 2
- These abnormalities are frequent even though approximately 60% of anorexia nervosa patients show normal laboratory values despite severe malnutrition 2
Comprehensive Metabolic Panel
- Electrolytes (sodium, potassium, chloride, bicarbonate) are crucial to detect hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis, particularly in patients with purging behaviors 1, 2
- Metabolic alkalosis occurs in 27.4% of patients, hypochloremia in 23.8%, and hypokalemia in 13.7% of those with purging behaviors 3, 4
- Liver enzymes assess hepatic function, which may be affected by malnutrition 1
- Renal function tests (BUN and creatinine) evaluate kidney function and hydration status 1, 2
Cardiac Assessment
Electrocardiogram Indications
- Obtain an ECG for patients with restrictive eating disorders, severe purging behaviors, or those taking medications known to prolong QTc intervals 1, 2, 5
- This is critical because patients with restrictive eating or severe purging require ongoing cardiac monitoring due to risk of sudden cardiac death 2
Additional Testing Based on Clinical Presentation
For Adolescents with Amenorrhea or Oligomenorrhea
- Obtain thyroid function tests (TSH and free T4) 2
- Consider hormonal workup to assess for hypothyroidism, hypercorticism, and hypogonadotropic hypogonadism, though these typically resolve with nutritional rehabilitation 2
For Suspected Bone Health Issues
- Measure 25-hydroxyvitamin D levels if low bone mineral density or bone stress injury is suspected 2
- Consider DXA scan for patients with prolonged amenorrhea due to long-term risk of osteopenia and osteoporosis 2
Critical Clinical Context
Vital Signs Assessment
- Measure temperature, resting heart rate, blood pressure, orthostatic pulse, and orthostatic blood pressure at initial evaluation 2
- Document height, weight, and BMI percentile or BMI Z-score (appropriate for adolescents) 2
- Assess for physical signs of malnutrition or purging behaviors such as Russell's sign, parotid enlargement, and dental erosion 2
Important 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 2, 6. This means you cannot rely on laboratory results alone to determine stability; clinical assessment remains paramount.
- Electrolyte abnormalities are found in 48.8% of patients with bulimia or atypical eating disorders, making them common but not universal 4
- The severity of laboratory abnormalities often correlates with BMI, but even severely malnourished patients may have normal labs 6
- Do not delay hospitalization based on normal laboratory values if clinical presentation suggests medical instability 2