Tissue transglutaminase antibodies, or tTG-IgA, blood test results produce a positive result in 98 percent of patients who do have celiac disease, and a negative result in 95 percent of patients who do not have celiac disease. In order for the positive result to be accurate, a patient with celiac disease must be consuming a diet that contains gluten, according to the Celiac Disease Foundation.
The tTG-IgA test can produce a false positive result in individuals who have associated autoimmune disorders such as type 1 diabetes, chronic liver disease, Hashimoto's thyroiditis, heart failure or rheumatoid arthritis. Other tests can be administered to check for conditions that would result in a false positive, such as the IgA endomysial antibody, or EMA, test, the total serum IgA test and the deaminated gliadin peptide test, states the Celiac Disease Foundation.
A genetic test for the genes HLA DQ2 and DQ8 can be done to verify that a person does not have celiac disease if other test results are inconclusive or if a patient is already consuming a gluten free diet and can't take the tTG-IgA test. All people with celiac disease have one or both of these genes, but 40 percent of the general population does as well. Therefore, the genetic test cannot be a conclusive test for the presence of celiac disease, the Celiac Disease Foundation reports.