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Celiac HLA DQ Association With Reflex to Celiac Antibodies tTG IgA/IgG With DGP IgA/IgG Pos/Neg Combination Screen
- Celiac Disease
- Deamidated Gliadin Antibodies (DGP)
- HLA DQ2
- HLA DQ8
- HLA Typing (DQ2, DQ8)
- Tissue Transglutaminase (tTG)
Aids in the diagnosis of celiac disease and other gluten sensitive enteropathies. The HLA DQ Association test provides genotyping for detection of HLA-DQ2 (DQA1*05:01 or 05:05 and DQB1*02:01 or *02:02) and HLA-DQ8 (DQB1*03:02). Patients with DQ2, half DQ2 and/or HLA DQ8 are predisposed to celiac disease. Patients who are positive for any of these celiac-associated alleles are reflexed to testing for a combination of celiac disease associated antibodies tTG and/or DGP, classes IgA and/or IgG. The results will be reported as positive if tTG and/or DGP of either antibody class are present.
A negative result from the HLA DQ Association test essentially rules out celiac disease. In addition to DQ2 and DQ8 status, the report also includes complete DQA and DQB genotypes, homozygosity for DQB1*02, and genetic risk assessment.
Celiac HLA DQ Association with Reflex to Celiac Antibodies tTG IgA/IgG with DGP IgA/IgG Pos/Neg Combination Screen is useful for individuals with symptoms suggestive of celiac disease and may be considered for asymptomatic relatives of patients with celiac disease to identify silent celiac disease (celiac antibody positivity not currently manifesting symptoms) or genetic predisposition to celiac disease. Early diagnosis of celiac disease and subsequent treatment with a strict gluten-free diet will control disease activity in most cases and can prevent secondary complications of the disorder.
The HLA DQ Association test detects celiac disease-associated alleles that predispose to the disorder but the test is not diagnostic of celiac disease. More than 95% of celiac disease patients are positive for DQ2, half DQ2, or DQ8, but many individuals with these genetic results do not develop celiac disease.
Celiac antibody testing has high but <100% sensitivity and specificity. Celiac antibody testing is not useful for celiac diagnosis in individuals on a gluten-free diet since these antibodies may no longer be present.
The Celiac Antibodies tTG IgA/IgG with DGP IgA/IgG Pos/Neg Combination Screen does not discriminate between the antibody types tested. A positive result indicates positivity for any individual or combination of the antibodies tTG IgA, tTG IgG, DGP IgA, DGP IgG. Even with appropriate precautions, an occasional specimen may not be satisfactory for testing. In such cases, fresh specimens should be collected for retesting.
HLA DQ Association: Polymerase chain reaction (PCR)/sequence-specific oligonucleotide probes (Luminex®). This is a class II antigen level and an allele level test. Celiac Antibodies: Enzyme Immunoassay (EIA)
Celiac disease is an autoimmune disorder characterized by a well defined genetic predisposition and sensitivity to gluten (found in wheat, barley and rye) that causes inflammation in the small intestine, villous atrophy, and malabsorption. Celiac disease can present with gastrointestinal symptoms and/or widely variable non-gastrointestinal findings such as iron deficiency anemia, dermatitis herpetiformis, osteoporosis, chronic fatigue, short stature, neurologic symptoms, and many more. Gastrointestinal symptoms are present in fewer than 50% of cases of symptomatic celiac disease. Strict avoidance of gluten in the diet will rid inflammation in most cases, and celiac-associated antibodies are likely to disappear with time.
Celiac disease affects approximately 1% of the US population, but only 17% of cases are currently diagnosed. Underdiagnosis is likely due to the variable presentation of celiac disease and clinical overlap with numerous other disorders such as IBS. The prevalence of celiac disease is increased in certain autoimmune disorders such such as insulin-dependent diabetes (~6%), thyroiditis (~2% to 4%) and Sjogren syndrome (~5%). It is also increased in Down syndrome (5% to 12%), Turner syndrome (~3%), Williams syndrome (3% to 10%) and selective IgA deficiency (~2% to 10%).
Genetic predisposition to celiac disease requires the presence of specific variants of the human leukocyte antigen (HLA) class II genes HLA-DQA1 and HLA-DQB1 to be present. These genes encode the alpha and beta chains of the celiac-associated proteins DQ2 and DQ8. Presence of DQ2, half DQ2 and/or DQ8 is required but not sufficient for the development of celiac disease. One or more of these HLA results are present in 30% of the population but overall, only 3% of these individuals develop celiac disease. The risk for developing celiac disease increases when there is a first degree relative with celiac disease (eg. the risk approaches 40% for sibs with the same HLA genotype as a patient with celiac disease).
Whole blood or buccal swabs and serum specimen should be collected to perform reflex assays if criteria is met.
7 mL blood or four buccal swabs and 0.5 mL serum
3 mL blood or two buccal swabs and 0.25 mL serum (Note: This volume does not allow for repeat testing).
EDTA blood and serum: 14 days; Buccal swab: 1 year
EDTA blood: 1 month; Serum: 14 days
Causes for Rejection
Incorrect sample type; lack of proper patient identification on the tube; Serum: hemolysis, lipemia, gross bacterial contamination
This combination antibody screen does not discriminate between the antibody types tested; The results will be reported as positive if any individual or combination of the antibodies tTG IgA, tTG IgG, DGP IgA, or DGP IgG is present.
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|164031||Celiac HLA Rflx to Ab Combo||167083||DQ2 (DQA1 0501/0505,DQB1 02XX)||4935-3|
|164031||Celiac HLA Rflx to Ab Combo||167084||DQ8 (DQA1 03XX, DQB1 0302)||41283-3|
|164031||Celiac HLA Rflx to Ab Combo||167085||Comment:||49549-9|
|164031||Celiac HLA Rflx to Ab Combo||167137||Additional Information:||48767-8|
|164031||Celiac HLA Rflx to Ab Combo||167086||QC||N/A|
|164031||Celiac HLA Rflx to Ab Combo||164021||Reflex to Celiac Ab Testing||N/A|
|Reflex Table for Reflex to Celiac Ab Testing|
|Order Code||Order Name||Result Code||Result Name||UofM||Result LOINC|
|Reflex 1||164040||tTG/DGP Screen||164041||tTG/DGP Screen||63420-4|