Sandbox:iqra

High probability (>5%)

• Duodenal biopsy • TTGA IgG

Both negative

Both positive

Serology/biopsy disagreement

Celiac disease unlikely

Celiac disease

Needs • HLA DQ2 and DQ8 genotyping •IgA level ± TTGA/DGP IgG •work up for other causes of villous atrophy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: : Iqra Qamar M.D.[2]

Laboratory Findings

Electrolyte and Biomarker Studies

• Complete blood count (CBC)
• Liver function tests (LFTs)
• B12
• Vitamin D
• Folate
• Ferritin (+/- Ca, alk phos) – at diagnosis and annually

Serologic Markers

Serologic tests may be divided into 2 groups based upon antibodies against respective antigens:

1. anti-TTG Ab tests
2. anti-gliadin antibody tests 

• IgA endomysial antibody (IgA EMA)
• IgA tissue transglutaminase antibody (IgA tTG)
• IgG tissue transglutaminase antibody (IgG tTG)
• IgA deamidated gliadin peptide (IgA DGP)
• IgG deamidated gliadin peptide (IgG DGP)

IgA endomysial assay:

• Endomysial antibodies bind to the endomysium and can be seen via indirect immunofluorescence producing a staining pattern. The target antigen is a tissue transglutaminase
• IgA EMA have high specificity and even low titres indicate a positive test result
• It has moderate sensitivity but high specificity for untreated celiac disease and is negative in treated patients.

Anti-tissue transglutaminase antibodies:

• These antibodies are directed against tissue transglutaminase-2 (tTG) antigen.
• They can be easily detected by ELISA
• Anti-tTG antibodies have high diagnostic accuracy

NOTE:

• Serum IgA EMA and IgA tTG have the highest diagnostic accuracy
• The IgA and IgG antigliadin antibody (AGA) are not recommended for estabilishing diagnosis as they have low accuracy and give more false positive results when compared with IgA tTG and IgA DGP assays
• The anti-deamidated gliadin peptide (DGP) assays also have high diagnostic accuracy

Sensitivity and Specificity of Antibody testing:

Literature review has shown that IgA endomysial and IgA tissue transglutaminase antibodies have a sensitivity more than 95% and a specificity almost 100%. However variations in results are seen among different laboratories.

Blood antibody tests for coeliac disease

Test	sensitivity	specificity
IgA enomysial antibody	85 to 98%	97 to 100%
IgA tissue transglutaminase antibody	90 to 98%	95 to 97%
IgA deamidated gliadin peptide	94%	99%
IgG deamidated gliadin peptide	92%	100%

Blood HLA tests for coeliac disease

Test	sensitivity	specificity
HLA-DQ2	94%	73%
HLA-DQ8	12%	81%