Celiac disease is an autoimmune condition where ingesting gluten (a protein found in wheat, barley, and rye) triggers an immune response. This response damages the small intestine’s lining, specifically the villi, impairing nutrient absorption and leading to various health issues. Since your sister has been diagnosed, your personal risk is significantly higher than that of the general population. Having a first-degree relative elevates your lifetime risk of developing the condition to approximately 1 in 10, compared to the general population’s risk of about 1 in 100. This genetic link is why doctors strongly advise screening for close family members, even if they are currently asymptomatic.
The Genetic Basis for Celiac Screening
Celiac disease has a strong hereditary component, meaning it runs in families due to specific genes that make a person susceptible to the condition. Nearly all people who develop celiac disease carry one or both of the human leukocyte antigen (HLA) genes, known as HLA-DQ2 and HLA-DQ8. These genes are involved in presenting foreign substances, like gluten, to the immune system.
The presence of the HLA-DQ2 or HLA-DQ8 genes is a necessary prerequisite for developing celiac disease, but it is not sufficient to cause the condition on its own. About 25 to 30% of the general population carries these genes, yet only a small fraction of these individuals will ever develop the autoimmune response. This means that while you must have these genes to get celiac disease, most people who have them will never receive a diagnosis.
The genetic link establishes your underlying susceptibility to the disease. First-degree relatives have a 10% risk because they are more likely to share these predisposing HLA genes. A genetic test can determine this susceptibility, which helps guide the need for continuous monitoring. The presence of the gene signals a genetic risk, but the active disease is an autoimmune process triggered by gluten exposure.
Steps for Celiac Testing in First-Degree Relatives
Testing for celiac disease in first-degree relatives begins with a simple blood test, which serves as the initial screening step. This serological testing checks for specific antibodies that the immune system produces in response to gluten in a person with celiac disease. The primary screening test measures the Tissue Transglutaminase IgA antibody (tTG-IgA), which is the most sensitive and preferred test for most patients.
It is crucial that you continue to eat a gluten-containing diet leading up to and during the blood test for the results to be accurate. If gluten has been removed from the diet, the damaged intestinal lining may begin to heal and the antibody levels may drop, leading to a false-negative result. A total serum IgA test is also typically ordered alongside the tTG-IgA to check for an IgA deficiency, a condition more common in people with celiac disease that can cause the tTG-IgA test to be falsely low or negative.
If a total IgA deficiency is identified, the doctor will instead order an IgG-based test, such as the Deamidated Gliadin Peptide IgG (DGP-IgG) or the Tissue Transglutaminase IgG (tTG-IgG). These alternative tests measure a different class of antibodies that are not affected by the IgA deficiency, ensuring an accurate screening.
If antibody blood test results are significantly elevated, a gastroenterologist typically recommends an upper endoscopy with a small bowel biopsy to confirm the diagnosis. The biopsy is considered the gold standard because it allows direct examination of the small intestinal lining for characteristic damage, such as villous atrophy. While blood tests screen for risk, the biopsy provides definitive proof of the disease’s active state.
Understanding Your Test Results and Next Steps
The interpretation of your test results will determine your next steps, guiding whether you need further intervention or ongoing monitoring. If your serology and subsequent biopsy are positive, you will receive a formal diagnosis of celiac disease. This outcome requires an immediate consultation with a gastroenterologist and a registered dietitian specializing in celiac disease to begin a strict, lifelong gluten-free diet.
If your initial antibody blood tests come back negative, this means you do not have active celiac disease at this time. However, a negative result does not completely eliminate the risk of developing it later in life, especially since you have a first-degree relative with the condition. For this reason, physicians often recommend a monitoring protocol, which may involve repeating the celiac serology every two to five years, or immediately if any symptoms suggestive of celiac disease begin to appear.
Another option is to undergo a genetic test for the HLA-DQ2 and HLA-DQ8 genes. Since these genes are required to develop celiac disease, a negative result on this genetic test essentially rules out the possibility of ever developing the condition. If you test negative for both the HLA-DQ2 and HLA-DQ8 genes, no further screening or monitoring for celiac disease is typically necessary.