Coeliac screen/ Tissue transglutaminase antibodies (TTg) IgA, TTG IgG
| Category | Immunology |
|---|---|
| Test background |
Coeliac disease is a gluten sensitive enteropathy affecting genetically-predisposed people (HLA DQ2/HLA DQ8) of all ages from infancy. Dermatitis herpetiformis (DH) is a blistering cutaneous manifestation of coeliac disease, these patients usually have mild gastrointestinal symptoms. DH is characterised by itchy vesicles on the forearms, elbows and buttocks. Coeliac disease is caused by an autoimmune reaction to dietary wheat gluten proteins (gliadin & glutenins) barley hordeins and rye secalins, following processing by the enzyme tissue transglutaminase (TTG). Autoantibodies to gliadin, deamidated gliadin, tissue endomysium and TTG can be detected in patients with coeliac disease. Of these positive antibodies against tissue transglutaminase IgA subclass (TTGA) are highly specific and sensitive for the diagnosis of coeliac disease. The gold standard test for dermatitis herpetiformis diagnosis is direct immunofluorescence on skin biopsy, although TTG IgA is present in a high proportion of these patients. In the paediatric population a TTG IgA result over 10x the upper limit of normal (i.e. >150 U/ml for our assay) together with a positive endomysium IgA result on two separate samples is sufficient to diagnose Coeliac disease without the requirement for a duodenal biopsy (ESPGHAN 2020). This assay measures TTG IgA and IgG antibodies using a magnetic bead based fluoroenzymeimmunoassay. As IgA deficiency is found at higher frequency in this patient group the assay has the ability to detect low IgA levels and will automatically test for TTG IgG instead. Newly TTG IgA positive patients will further be tested for IgA endomysial antibodies by indirect immunofluorescence on primate tissue. |
| Clinical Indications |
Suspected gluten sensitivity Testing is also recommended in at risk groups (type 1 diabetes, trisomy 21 syndrome, autoimmune thyroid and liver disease and first degree relatives of people with coeliac disease). |
| Reference range | <15 U/mL |
| Sample & container required | Serum (rust top RST tube) |
| Sample volume | 5-10 mL blood (1 mL serum) |
| Turnaround time | 7 days |
| Notes | This test is currently unaccredited due to a relocation of the analyser (no changes to assay used) |