Assay

Tissue transglutaminase (TTG) antibodies

Key Words

Tissue transglutaminase IgA  antibodies , TTGA

Specimen Collection

Serum (Brown)

Turnaround time

5 days

Test indications

IgA anti-tTG antibodies are indicated as a screening test for Coeliac disease.  As per NICE guidance (https://www.nice.org.uk/guidance/ng20/chapter/Recommendations [1]) patients must have commenced a normal diet (eating some gluten in more than one meal every day) for at least 6 weeks before testing. The presence of IgA antibodies to tTG closely correlates with the detection of endomysial antibodies detected by indirect immunofluorescence but have the advantage that they are reported quantitatively. All newly positive anti-tTG results will be confirmed by endomysial antibodies.  In known coeliac patients anti-tTG concentrations may predict recovery of villous atrophy as concentrations have an inverse relationship with adherence with a gluten free diet.  As patients with IgA deficiency (found in up to 1/500 of the normal population) can cause false negative results, all likely low/deficient patients will automatically have total IgA and anti-IgG tTG measured.

False positive anti-tTG results have been described in patients with liver disease.  False negative results can be found in patients with IgA deficiency (but unlikely to occur with testing strategy in place).  The gold standard diagnosis is duodenal biopsy and histological confirmation.

Please see new guidelines from ESPGHAN for the diagnosis of Paediatric Coeliac disease. https://www.espghan.org/knowledge-center/publications/Clinical-Advice-Guides/2020_New_Guidelines_for_the_Diagnosis_of_Paediatric_Coeliac_Disease [2]

Methodology

Enzyme immunoassay

Interferences

No known methodological interferences

Reference Range

IgA and IgG TTG

Negative : <7 U/mL

Equivocal: 7-10 U/mL

Positive: >10 U/mL

Analytical error

Contact the laboratory (x8454)

Reference change value

NA

Minimum retesting interval

Requests made within 30 days of a previous request on a patient are intervened.