Could the patient have celiac disease?

Diagnostic Approach to Possible/Probable Celiac Disease

For adults with suspected celiac disease, start with IgA anti-tissue transglutaminase (TG2-IgA) serology while the patient is consuming gluten, and if strongly positive (>10× upper normal limit), you can now conditionally proceed without biopsy in select cases, though duodenal biopsy remains the traditional gold standard for confirmation. 1, 2

Initial Serologic Testing

The diagnostic algorithm begins with IgA TG2 antibody testing as your primary screening tool 1, 3:

• High-titre positive (>10× ULN): Virtually diagnostic when combined with positive endomysial antibody on a second sample (PPV ~100%) 1
• The 2025 ESsCD guidelines now conditionally support a no-biopsy approach for selected adults with IgA TG2 ≥10× ULN, representing a major shift from traditional practice 2
• Always check total IgA levels concurrently, as IgA deficiency occurs in ~2-3% of celiac patients and will cause false-negative IgA-based testing 1

Critical Pitfall: The Gluten Requirement

Patients MUST be consuming gluten at the time of testing - both serology and biopsy sensitivity plummet on gluten-free diets 1. If a patient has already started avoiding gluten:

• Restart normal diet with 3 slices of wheat bread daily for 1-3 months before repeat testing 1
• Some patients require even longer gluten challenge (up to several years in rare cases) 3

When to Proceed to Biopsy

Despite the new no-biopsy option, duodenal biopsy remains indicated in most scenarios 1, 2:

Biopsy is Essential When:

• TG2-IgA is positive but <10× ULN
• Clinical suspicion is high despite negative serology
• Differential diagnosis is needed (other causes of villous atrophy)
• Patient presentation is atypical or complex

Proper Biopsy Technique:

• Obtain at least 4-6 specimens from the second part of duodenum or beyond 3, 2
• Avoid relying solely on duodenal bulb biopsies (Brunner's glands and peptic changes interfere) 3
• Mucosal changes can be patchy, making multiple samples critical 3

The diagnostic histology shows: moderate-to-severe villous atrophy with crypt hyperplasia and increased intraepithelial lymphocytes 4. Isolated intraepithelial lymphocytosis without architectural changes is insufficient for diagnosis 3.

Special Testing Scenarios

IgA Deficiency (2-3% of celiac patients):

If total IgA is low, switch to:

• IgG-based testing: IgG deamidated gliadin antibody or TG2-IgG 1
• Note: IgG TG2 is NOT specific in patients with normal IgA levels 1

Seronegative but High Clinical Suspicion:

1. Verify patient was consuming adequate gluten during testing
2. Consider HLA-DQ2/DQ8 testing - its value lies in its negative predictive value 1, 3
   • ~95% of celiac patients have DQ2, ~5% have DQ8
   • Absence of both alleles effectively rules out celiac disease
   • However, 40% of general population carries these alleles, so presence doesn't confirm diagnosis 3
3. Proceed to biopsy if HLA-positive or clinical suspicion remains very high 3

Recognizing Atypical Presentations

Don't limit your suspicion to classic diarrhea and malabsorption 5, 6, 4. Test for celiac disease when patients present with:

Gastrointestinal:

• Chronic diarrhea, bloating, flatulence, abdominal pain
• Weight loss, poor appetite

Hematologic:

• Iron deficiency anemia (even without GI symptoms) 5, 4
• Unexplained anemia

Metabolic/Endocrine:

• Unexplained hypoalbuminemia/hypoproteinemia 7
• Hypothyroidism or thyroid autoimmunity 4
• Elevated liver enzymes (hepatocellular or cholestatic pattern) 4

Musculoskeletal:

• Osteopenia/osteoporosis 7, 4
• Pathologic fractures 7
• Polyarthralgia 4

Neuropsychiatric:

• Depression, anxiety, anhedonia 4
• Idiopathic ataxia 5

Other:

• Infertility 5
• Idiopathic short stature 5

High-Risk Groups Requiring Screening

Screen even asymptomatic individuals with 5:

• Type 1 diabetes
• Down syndrome
• First-degree relatives of celiac patients
• Autoimmune thyroid disease

Avoiding Common Diagnostic Errors

1. Never advise gluten avoidance before completing diagnostic workup - this is the most common reason for diagnostic failure 1

2. Don't rely on visual endoscopy alone - endoscopic appearance is not sufficiently sensitive; always biopsy 3

3. Don't use IgG testing in IgA-sufficient patients - it lacks specificity 1

4. Don't diagnose based on isolated intraepithelial lymphocytosis - requires villous architectural changes 3

5. Don't skip confirmatory serology if biopsy was done first - obtain celiac-specific antibodies before starting gluten-free diet 1

The strongest recent evidence from 2025 ESsCD guidelines 2 and 2019 AGA expert review 1 supports this algorithmic approach, balancing the new conditional no-biopsy pathway with the continued importance of histologic confirmation in most clinical scenarios.