What tests and investigations are used to diagnose and manage Anorexia Nervosa?

Tests and Investigations for Anorexia Nervosa

All patients with suspected anorexia nervosa require vital signs measurement, anthropometric assessment, complete blood count, comprehensive metabolic panel, and electrocardiogram at initial evaluation, even though approximately 60% will have normal laboratory values despite severe malnutrition. 1, 2

Initial Clinical Assessment

Vital Signs and Physical Measurements

• Measure temperature, resting heart rate, blood pressure, orthostatic pulse (change >20 bpm), and orthostatic blood pressure (drop >10 mmHg systolic) at every evaluation. 1, 2
• Document height, weight, and calculate BMI (or percent median BMI, BMI percentile, or BMI Z-score for children and adolescents). 1, 2
• Determine total weight loss and weight status (percent below ideal body weight). 3
• Assess for physical signs of malnutrition or purging behaviors including Russell's sign (calluses on knuckles), parotid gland enlargement, and dental erosion. 1

Historical Information to Obtain

• Calculate types and frequency of purging behaviors (vomiting, laxative use, excessive exercise, starvation). 3
• Assess degree of obsession with food and weight, understanding of diagnosis, and willingness to receive help. 3
• Evaluate functioning at home, school, and with peers. 3
• Screen for comorbid psychiatric diagnoses including depression, anxiety, obsessive-compulsive disorder, and suicidal ideation. 3
• Assess history of physical or sexual abuse. 3

Essential Laboratory Tests

Core Blood Work

• Order complete blood count to detect anemia, leukopenia, and thrombocytopenia. 1, 2
• Obtain comprehensive metabolic panel including sodium, potassium, chloride, bicarbonate, BUN, creatinine, glucose, and liver enzymes. 1, 2
  • Hypokalemia and hypochloremic alkalosis indicate purging behaviors. 3
  • Hyponatremia or hypernatremia suggest fluid manipulation for weight control. 3
  • Hypoglycemia has prognostic significance and indicates severe malnutrition. 4

Cardiac Evaluation

• Perform electrocardiogram in all patients with restrictive eating disorders or severe purging behaviors to assess for QTc prolongation, which predicts risk of sudden cardiac death. 1, 2
• Monitor QTc intervals serially in patients with ongoing restrictive eating or severe purging. 1
• QTc prolongation has diagnostic and prognostic value for medical instability. 4

Endocrine Testing

• Obtain thyroid function tests (TSH and free T4) in patients with oligomenorrhea or amenorrhea. 1
• Consider hormonal workup for hypothyroidism, hypercortisolism, and hypogonadotropic hypogonadism, though these typically resolve with nutritional rehabilitation and do not require specific treatment. 1

Bone Health Assessment

• Consider DXA scan for patients with prolonged amenorrhea (>6 months) due to long-term risk of osteopenia and osteoporosis, which represents one of the few irreversible complications. 1, 4
• Measure 25-hydroxyvitamin D levels if low bone mineral density or bone stress injury is suspected. 1
• Bone mineral density loss correlates more with amount of weight loss than with specific low-weight cut-offs in adolescents. 4

Critical Clinical Caveat

Normal laboratory test results do not exclude serious illness or medical instability—approximately 60% of anorexia nervosa patients show normal values on routine testing even with severe malnutrition. 1, 5 This is the most important pitfall to avoid, as relying solely on laboratory values without comprehensive clinical assessment can delay life-saving treatment. 5 Even in the subgroup with BMI <14.15 kg/m², fewer than 50% of laboratory tests show abnormalities. 5

Severity Stratification

The combination of clinical and laboratory findings determines treatment setting:

• Severe bradycardia (<40 bpm), hypotension, hypothermia, severe electrolyte abnormalities, or QTc prolongation require immediate hospitalization for medical stabilization before transfer to specialized eating disorder programs. 1
• Orthostatic vital sign changes have diagnostic and prognostic significance for medical instability. 4
• The degree of medical compromise guides whether outpatient, intensive outpatient, or inpatient treatment is appropriate. 5

Psychosocial Evaluation Components

• Assess suicidality at every visit, as 25% of anorexia nervosa deaths result from suicide. 1
• Evaluate parents' reaction to illness, as denial or disagreement about treatment approach can exacerbate the condition. 3
• Screen for anxiety, phobia, obsessive thoughts, and compulsive behaviors that may worsen during nutritional rehabilitation. 6