Is a skin test used to diagnose celiac disease?

No Skin Test for Celiac Disease Diagnosis

There is no skin test used to diagnose celiac disease. 1, 2 The diagnosis of celiac disease relies primarily on blood tests (serology) and intestinal biopsies, not skin testing.

Proper Diagnostic Approach for Celiac Disease

Step 1: Serological Testing

• The primary screening test is IgA tissue transglutaminase antibody (tTG-IgA) 2
  • Sensitivity: ~97.7% in children
  • Specificity: ~70.2% in children
• Other serological tests include:
  • IgA endomysial antibodies (EMA-IgA)
  • Deamidated gliadin peptide antibodies (DGP)

Step 2: Confirmation with Intestinal Biopsy

• Upper endoscopy with small bowel biopsy is essential for diagnosis 1
• Multiple duodenal biopsies are required:
  • 1-2 from the duodenal bulb
  • At least 4 from the distal duodenum
• Histological findings include:
  • Villous atrophy
  • Crypt hyperplasia
  • Increased intraepithelial lymphocytes

Special Considerations

• IgA deficiency occurs in 2-3% of celiac patients 2

  • Can lead to false-negative tTG-IgA results
  • In suspected IgA deficiency, total serum IgA should be measured
  • If IgA deficient, IgG-based testing (IgG-tTG or IgG-DGP) should be used

• HLA-DQ2/DQ8 genetic testing 2

  • Not for routine diagnosis
  • High negative predictive value (>99%)
  • Useful in specific scenarios:
    • Patients with negative serology but strong clinical suspicion
    • Patients already on gluten-free diet without prior testing
    • Patients with equivocal biopsy results

Tests NOT Recommended for Celiac Disease Diagnosis

The American College of Gastroenterology specifically states that the following tests should NOT be used for celiac disease diagnosis 1:

• Stool studies
• Small-bowel follow-through
• Intestinal permeability testing
• D-xylose testing
• Salivary testing
• Skin testing (not mentioned as a diagnostic option in any guidelines)

Common Pitfalls in Diagnosis

1. Testing while on a gluten-free diet

   • Serological tests and biopsies should be performed while the patient is on a gluten-containing diet
   • Gluten must be consumed for at least several weeks before testing

2. Inadequate biopsy sampling

   • Multiple biopsies (at least 6 specimens) are essential for accurate diagnosis
   • Patchy distribution of intestinal damage can lead to false negatives with insufficient sampling

3. Confusing non-celiac gluten sensitivity with celiac disease

   • Non-celiac gluten sensitivity should only be considered after celiac disease has been ruled out
   • Requires negative celiac serology and normal duodenal biopsies while on a gluten-containing diet

4. Relying solely on symptom response to gluten-free diet

   • Improvement of symptoms after starting a gluten-free diet has a very low positive predictive value for celiac disease 1
   • Should not be used for diagnosis without supporting evidence

Remember that celiac disease can present with various symptoms beyond gastrointestinal complaints, including iron deficiency anemia, osteoporosis, neurological symptoms, and dermatitis herpetiformis (a skin manifestation of celiac disease that does require skin biopsy for its diagnosis, but this is distinct from diagnosing celiac disease itself).