Celiac disease is an autoimmune condition where ingesting gluten, a protein found in wheat, barley, and rye, triggers an immune reaction that damages the small intestine. This damage, known as villous atrophy, impairs the body’s ability to absorb nutrients. This can lead to a wide range of symptoms and complications, including chronic diarrhea, anemia, and fatigue. Understanding the proper sequence and location of diagnostic tests is key for anyone seeking clarity on their symptoms or genetic risk.
Initiating the Testing Process
The first step in seeking a diagnosis is to consult a licensed medical professional, typically a Primary Care Provider (PCP) or a Pediatrician. During this initial appointment, the provider evaluates symptoms, medical history, and risk factors to determine if Celiac disease testing is appropriate. Symptoms are highly varied, ranging from digestive issues like abdominal pain to non-digestive problems such as anemia and fatigue. If Celiac disease is suspected, the PCP will initiate the diagnostic process by ordering initial blood work. It is important that a patient continues to consume gluten regularly throughout this period, as stopping gluten before testing can lead to inaccurate, false-negative results.
The Role of Blood Screening
Initial screening takes place at a laboratory where a blood sample is drawn for serological testing. This testing detects specific antibodies produced by the immune system in response to gluten. The primary test is the tissue Transglutaminase IgA antibody (tTG-IgA), which is highly sensitive for Celiac disease. Providers also test for total serum Immunoglobulin A (IgA) because IgA deficiency can cause a falsely negative tTG-IgA result, requiring the use of an IgG-based test (DGP-IgG or tTG-IgG) instead. For the most accurate results, a patient should consume gluten daily for at least six weeks prior to the blood draw. While a positive blood test strongly suggests the disease, it does not provide a definitive diagnosis on its own.
Confirmatory Procedures and Specialist Involvement
If the blood screening is positive, the patient is referred to a Gastroenterologist for the next stage of testing. This specialist performs an upper gastrointestinal endoscopy at a hospital or surgical center. The endoscopy is necessary to obtain definitive proof of intestinal damage required for diagnosis. During the procedure, the Gastroenterologist inserts a flexible tube with a camera into the small intestine (duodenum) to take multiple tissue samples, or biopsies. A pathologist then examines these samples under a microscope to look for characteristic damage, such as the flattening of the villi, which confirms the diagnosis.
Testing Asymptomatic Relatives
Immediate family members of someone diagnosed with Celiac disease have a higher risk of developing the condition. Screening is recommended for these relatives, even if they are asymptomatic, due to the possibility of “silent” Celiac disease. Screening begins with the same initial serology blood tests, such as tTG-IgA, performed at a lab. Another option is genetic testing, which uses a blood or saliva sample to look for the human leukocyte antigen (HLA) genes, specifically HLA-DQ2 and HLA-DQ8. While nearly all people with Celiac disease carry these genes, the test is most useful for its high negative predictive value: if the genes are absent, Celiac disease can be almost entirely ruled out.