What are the causes of elevated fecal calprotectin in a teenage girl with malabsorption?

Causes of Elevated Fecal Calprotectin in a Teenage Girl with Malabsorption

In a teenage girl with malabsorption and elevated fecal calprotectin, the primary differential includes inflammatory bowel disease (IBD), celiac disease, gastrointestinal infections, food intolerances/malabsorption syndromes (particularly lactose intolerance), and rare conditions like collagenous gastritis.

Algorithmic Approach to Diagnosis

Step 1: Rule Out Infectious Causes First

• Test for Clostridioides difficile and other enteric pathogens 1
• Gastrointestinal infections are among the most common causes of elevated calprotectin in children
• In pediatric studies, 89% of children with calprotectin >500 μg/g had either infectious diarrhea or IBD 2

Step 2: Assess Calprotectin Level to Guide Urgency

Calprotectin interpretation in adolescents:

• <150 μg/g: Lower likelihood of significant mucosal inflammation; consider functional disorders with food intolerance
• 150-500 μg/g: Intermediate range; requires further workup but may represent food intolerance/malabsorption
• >500 μg/g: High likelihood of IBD or active infection requiring urgent evaluation 2

Step 3: Evaluate for Food Intolerances/Malabsorption

Key conditions to test:

• Lactose intolerance (most commonly associated with elevated calprotectin among food intolerances) 3
• Fructose malabsorption 3
• Histamine intolerance 3
• Celiac disease (tissue transglutaminase antibodies, total IgA) 4, 5

Important finding: In a study of 228 IBS-spectrum patients with food intolerances, 17.1% had elevated calprotectin, with lactose intolerance being the most common association. Notably, calprotectin levels significantly decreased or normalized after implementing targeted elimination diets 3.

Step 4: Consider IBD (Crohn's Disease or Ulcerative Colitis)

When to strongly suspect IBD:

• Persistent elevation of calprotectin despite dietary modifications
• Calprotectin >250 μg/g has 76% sensitivity and 74% specificity for endoscopically active Crohn's disease 6
• Associated alarm features: persistent diarrhea, rectal bleeding, weight loss, anemia
• Abnormal platelet levels or abdominal ultrasound findings 2

Proceed to endoscopy if:

• Calprotectin remains elevated on repeat testing (3-6 months)
• Clinical symptoms persist despite dietary intervention
• Any alarm features present

Step 5: Rare but Important Causes in Adolescent Females

Collagenous gastritis 4:

• Presents with chronic abdominal pain and iron deficiency anemia
• Can cause markedly elevated calprotectin (507-796 μg/g reported)
• Requires esophagogastroduodenoscopy with gastric biopsies showing thickened subepithelial collagen bands
• Consider when ileocolonoscopy is normal but symptoms and elevated calprotectin persist

Critical Pitfalls to Avoid

1. Don't assume all elevated calprotectin means IBD: In children with calprotectin 51-249 μg/g, the majority do NOT have IBD 2. Food intolerances are common and treatable causes.

2. Repeat testing is valuable: Except in patients with IBD, calprotectin levels significantly reduce on repeat testing, making serial measurements diagnostically useful 2

3. Consider upper GI pathology: If colonoscopy is normal but calprotectin remains elevated, perform upper endoscopy to evaluate for collagenous gastritis or other gastric pathology 4

4. Test variability matters: Use the same calprotectin assay for serial measurements, as assays are not interchangeable and there is substantial within-day variation 1

5. Non-GI inflammation can elevate calprotectin: Swallowed inflammatory exudate from oral lesions can falsely elevate levels 7, though this is less relevant in malabsorption presentations

Practical Management Algorithm

For calprotectin 150-500 μg/g with malabsorption:

1. Stool culture and C. difficile testing
2. Celiac serology
3. Hydrogen breath testing for lactose/fructose malabsorption
4. Trial of targeted elimination diet based on suspected intolerance
5. Repeat calprotectin in 3-6 months
6. If persistently elevated → endoscopy (both upper and lower)

For calprotectin >500 μg/g:

1. Urgent stool studies for infection
2. Complete blood count, CRP, albumin
3. If infection excluded → proceed directly to endoscopy for IBD evaluation 2

The evidence strongly supports that food intolerances, particularly lactose intolerance, are underrecognized causes of elevated calprotectin in adolescents 3, and therapeutic trials of targeted diets can both diagnose and treat these conditions before pursuing invasive testing.