It Starts with a Blood Test
How Should a Diagnosis of Celiac Disease Be Conducted?
Blood tests are the first step in diagnosing celiac disease and can help determine the need for further evaluation for confirmation of celiac disease. It is important that patients continue to consume gluten as normal and do not start a gluten-free diet, as this can result in false negative test results.
Although high titers in serological testing are indicative of celiac disease, they alone do not provide a definitive diagnosis of celiac disease and a biopsy of the small intestine is required for a definitive diagnosis1. Similar to serological testing, a normal, gluten-containing diet must also be maintained in order for the histological testing to be accurate.
There are several serological tests that are sensitive in the evaluation of celiac disease. These include antibodies to:
- Deamidated gliadin
Tissue transglutaminase antibody (tTG)-IgA in adults and most children is reported with a sensitivity and specificity greater than 90% and 95%, respectively2-4. Endomysial antibody (EMA)-IgA usually correlates with tTG. It is more costly and is identified manually, thus it is not the first line marker4.
The IgA-tTG is the best choice for both the adult and most pediatric populationsSome research indicates that IgA-EMA or IgA-tTG is, in fact, as comparable or more accurate than antigliadin (AGA) antibodies among children younger than three years old 2,5-8.
In recent years, testing for IgA and IgG antibodies to deamidiated gliadin peptide (DGP) have been clinically introduced and available2. The DGP antibody has a remarkably higher specificity for celiac disease than native gluten, the anti-gliadin (AGA) antibodies2,9. In particular, IgA/IgG antibodies to DGP are useful among patients who have selective Immunoglobulin A (IgA) deficiency2. IgA deficiency is between 10 to 15 times more common among patients with celiac disease than in the general population, occurring in an estimated 2% to 3% of patients with celiac disease. Thus, total IgA should be quantified. Notably, IgA/IgG anti-DGP testing provides a valuable alternative to IgG anti-tTG testing in the case of IgA deficiency2, 10. It is important to note that because of accuracy and cost matters, IgA anti-tTG with total IgA levels be the first choice for testing on the population level, followed by IgA/IgG anti-DGP testing in patients who are IgA deficient2.
Since the levels of anti-tTG and EMA tend to wane in the absence of gluten ingestion, these markers are useful to monitor adherence to a gluten-free diet. This serology may be checked 3 to 6 months after diagnosis and from then forward minimally once approximately every year in patients who are in clinical remission. Testing can also be performed at any time in individuals with persistent or recurrent symptoms11.
Further, serologic testing can be conducted on patients who were diagnosed in the past but have been followed by a physician for a suboptimal length of time. Additionally, serology tests have a role in monitoring patient’s who were told they “outgrew celiac disease” at one point in time. Celiac disease is a lifelong autoimmune condition that cannot be outgrown and the only treatment is a strict gluten-free diet.
Finally, it is particularly important to note that because the sensitivity and specificity vary significantly among each of the celiac disease serum antibody assays, it has been recently recommended that physician groups indicate the specific antibody test1.
What does the Quest Diagnostics panel include?
Tests available include Tissue Transglutaminase Antibody (IgA) (test code 8821) and Endomysial Antibody Screen (IgA) with Reflex to Titer (test code 15064).
Physicians and hospitals can initiate testing for celiac disease by assessing the following antibodies. Celiac disease serology will normalize if the patient is on a gluten-free diet. Therefore, confirm that the patient is maintaining a normal, gluten-containing diet in order to ensure for the most accurate test results.
- Total Immunoglobulin A Antibody (test code 539)
- IgA-tTG (test code 8821)
- If the IgA-tTG is positive, IgA-EMA with Reflex to IgA-EMA Titer (test code 15064) will be performed.
- If total IgA concentration is low IgG-tTG antibody test (test code 11070) will be performed.
- Deamidated Gliadin Peptide Antibody (IgA (test code 11228/IgG (test code 11212)can be ordered for IgA deficient patients as well .
What is the next step if serology is positive?
An esophagogastroduodenoscopy (EGD) and biopsy should be performed on the small intestine with 4-6 samples, one including the duodenal bulb1. Primary care providers and other non-gastroenterology specialists should refer patients to a gastroenterologist in order to confirm celiac disease. Remember, a normal, gluten-containing diet must also be maintained in order for the histological testing to be accurate.
What is the Function of Genetic Testing?
Complex genetics contribute to pathology as typical dominant or recessive traits are not followed16. The most contributory genetic material is the HLA class II: HLA-DQ2 (DQA1*05/DQB1*02), which is the most common, and/or HLA-DQ8 (DQA1*03/DQB1*0302) genes17. One or both of these are present in celiac disease, accounting for up to 40% of the genetic load17. Different alpha and beta variants exist and can determine disease risk. Quest identifies these to allow for individual patient interpretation. Examples of high risk variants include HLA-DQA1*03, HLA-DQA1*05, HLA-DQB1*0201 and HLA-DQB1*0302. A high negative predictive value is appreciated so if these genes are absent it is very unlikely that celiac disease can manifest18. Though the genes are common, presenting in approximately 30% to 40% of the general population in Americans and Europeans, only 1% to 3%-4% respectively develop celiac disease18. Family members of persons with celiac disease who have positive genetic testing are at an increased risk for developing celiac disease and should have their serology tested for celiac disease. While a consensus on the timeline of serology testing of family members of persons with diagnosed celiac disease does not exist at this time, clinical practices generally recommend follow-up testing every 1 to 3 years.
In what cases should you consider genetic testing?
Genetic testing is first and foremost a tool to rule out the risk for developing celiac disease. It is the only celiac disease test that does not have to be performed on a normal, gluten-containing diet. Genetic testing is particularly useful in infants and children with familial history or suspected celiac disease16. Genetic testing when negative in these young patients can spare the concern for disease surveillance for life. When accounting for other factors it is considered useful to aid in diagnosis. Some scenarios include young children who don’t produce adequate tTG or EMA antibodies, those on immunosuppressant drugs and those with other potential conditions causing the same histological changes in the small intestine as those of celiac disease1, such as giardia, milk allergy and other autoimmune diseases like Crohn’s.
Most especially, genetic testing can provide guidance with a particular dilemma that seems to be currently widespread – self-diagnosis of a gluten-related disorder. In those patients without a formal diagnosis, having self initiated the gluten-free diet for several months, having negative antibodies and/or biopsy and who will not undergo gluten challenge genetic testing can provide a scientific approach to an obscure scenario16.
Quest Diagnostics offers HLA typing for celiac disease. More information can be found here.
Once diagnosed, what are some other parameters you should check at baseline and during the management of celiac disease?
The National Institutes of Health (NIH) Consensus Statement on Celiac Disease recommends the following five key elements to celiac disease management19:
- Consultation with a skilled dietitian
- Education about the disease
- Lifelong adherence to a gluten-free diet
- Identification and treatment of nutritional deficiencies
- Access to an advocacy group
- Continuous long-term follow-up by a multidisciplinary team
Quest Diagnostics provides you with the following information and resources as your partner in helping you to facilitate and fulfill these five important elements. Additional information can be found at Quest Diagnostics Physicians and Hospitals Gluten-Related Disorders pages within the Helping Your Patients section.
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(Name change January 1, 2012: Academy of Nutrition and Dietetics)
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16. Leffler, D., Dennis, M. Real Life with Celiac Disease. AGA. Bethesda, MD. 2010.
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