Collect 6 ml Gold/SST blood tube, centrifuge then aliquot 4.0 mL serum; (2.0 mL minimum), store refrigerated and transport to the lab within 7 days, or freeze at -20ºC.

Plasma and other body fluids, hemolyzed specimens.

Store refrigerated and transport to the lab within 7 days, or freeze at -20ºC.

Performed Mon-Fri. Specimens must be received by 1500.

TTG IgA performed in Microbiology.
IGA performed in Special Chemistry.

Performed Mon-Fri. Specimens must be received by 1500.

TTG IgA performed in Microbiology.
IGA performed in Special Chemistry.

Immunoglobulin A (IGA) Quantitative

Limit of detection: levels < 7 mg/dL are considered deficient in this test battery.

Tissue Transglutaminase IgA (tTG-IgA)

Reference ranges:

Negative: =19 units

Weak Positive: 20-30 units

Moderate to Strong Positive: =31 units

Interpretation:

Positive results indicate presence of tTG-IgA antibodies and suggest gluten sensitivity-related enteropathies.

Negative results indicate no tTG-IgA antibodies or levels below the cut-off of this particular assay.

Deaminated Gliadin Peptide Immunoglobulin G (DGP-IgG)  (will only be reflexed for testing if IgA quantitative <7 mg/dL) - (RPS order code GLIGG)

Reference ranges:

Negative: =19 units

Weak Positive: 20-30 units

Moderate to Strong Positive: =31 units

The Clinical Microbiology Laboratory will offer a new test called “Celiac Disease Screen” starting March 1, 2012.  This screen will include two tests: tissue transglutaminase IgA (tTG-IgA) and immunoglobulin A (IgA) quantitative.  The screen will also include a reflex test for deaminated gliadin peptide-IgG (DGP-IgG) if the IgA quantitative is < 7 mg/dL.   This new order set of tests will provide for more uniform practice in screening for celiac disease at TNMC.  Celiac disease is a genetically (HLA-DQ2/DQ8) associated autoimmune mediated disease of the small intestine triggered by consumption of gluten peptides.  During the course of celiac disease, antibodies develop against the gliadin portion of gluten and autoantibodies develop against tTG.  Autoantibodies to tTG have a higher diagnostic value than anti-gliadin detection. Since IgA is the most abundant gastrointestinal antibody produced, this antibody is targeted for diagnostic purposes. Celiac disease is associated with selective IgA deficiencies with a general frequency in the population of 1:400.  Deaminated gliadin peptide IgG has a higher diagnostic value than conventional gliadin IgG and is recommended when IgA is deficient.  The relative sensitivity of the tTG-IgA assay is 93% and specificity is 92%.  In low probability cases the Celiac Disease Screen is recommended.  For a high probability case, it is recommended for the patient to have both a duodenal biopsy and serum tTG-IgA.  tTG-IgA can also be used to monitor adherence to a strict gluten-free diet since IgA levels decline in the absence of gluten and is available to order separately.  To monitor treatment, the tTG-IgA alone can be retested 6 months after initiation of a gluten-free diet and then monitored annually.