What labs should be ordered for a gluten sensitivity test?

Laboratory Testing for Gluten Sensitivity (Celiac Disease)

Order IgA tissue transglutaminase (tTG-IgA) as the primary screening test, combined with total IgA level to rule out IgA deficiency. 1

Primary Screening Panel

The essential initial laboratory workup consists of:

• IgA tissue transglutaminase (tTG-IgA): This is the preferred first-line test with sensitivity of 90-97% and specificity of 96-100% 1, 2
• Total IgA level: Must be measured simultaneously because IgA deficiency occurs in 1-3% of celiac disease patients and causes falsely negative tTG-IgA results 1

Critical Pre-Testing Requirement

The patient must be consuming gluten at the time of testing. All diagnostic serologic testing must be performed before initiating a gluten-free diet, as gluten withdrawal causes antibody levels to decline and produces false-negative results 1, 2. If the patient has already reduced gluten intake, they should consume at least three slices of wheat bread daily for 1-3 months before testing 1

Additional Testing Based on Initial Results

If IgA Deficiency is Detected (Low Total IgA):

• IgG deamidated gliadin peptide (DGP-IgG): This is the preferred test in IgA-deficient patients with superior diagnostic accuracy (93.6% sensitivity, 99.4% specificity) 3, 4
• IgG tissue transglutaminase (tTG-IgG): Alternative option, though less reliable than DGP-IgG 1

If tTG-IgA is Positive:

• IgA endomysial antibody (EMA): Confirmatory test with excellent specificity of 99.6% in adults 1, 3, 2
• When tTG-IgA exceeds 10 times the upper normal limit combined with positive EMA in a second blood sample, the positive predictive value for celiac disease is virtually 100% 1

For Children Under 2 Years:

• Combine tTG-IgA with both IgG and IgA deamidated gliadin peptides to improve sensitivity 1, 4

Tests NOT Recommended

Do NOT order:

• Native gliadin antibodies (AGA): No longer recommended for primary detection 1
• IgG tissue transglutaminase alone (without documented IgA deficiency): Not specific in the absence of IgA deficiency 1
• HLA-DQ2/DQ8 testing as initial screening: Limited diagnostic role; primarily useful for its negative predictive value to rule out celiac disease in equivocal cases 1

Important Distinction: True Gluten Sensitivity vs. Celiac Disease

If you are asking about non-celiac gluten sensitivity (a distinct entity from celiac disease), the serological pattern differs significantly:

• IgG AGA may be positive in 56.4% of cases 5
• IgA AGA may be positive in only 7.7% of cases with lower titers than celiac disease 5
• tTG-IgA, EMA, and DGP-IgG are negative in non-celiac gluten sensitivity 5
• However, there are no validated diagnostic markers for non-celiac gluten sensitivity, and diagnosis requires exclusion of celiac disease first 5

Common Pitfalls to Avoid

• Never start a gluten-free diet before completing diagnostic workup, as this leads to false-negative serology and inconclusive biopsies 1, 3
• Do not rely on symptoms alone to differentiate celiac disease from other gastrointestinal disorders 1
• Do not skip total IgA measurement, as missing IgA deficiency is a frequent cause of false-negative results 1
• Do not combine multiple tests initially in low-risk populations, as this reduces specificity without meaningful improvement in sensitivity 1

Next Steps After Positive Serology

Positive serology requires confirmation with upper endoscopy and duodenal biopsy (at least 4-6 specimens from the distal duodenum) as the gold standard for diagnosis 1, 3, 2. Serology alone, even with high titers, is insufficient for definitive diagnosis without histologic confirmation 1.