Sorting out celiac disease with serologic testing

In the U.S., the American Gastroenterological Association issued a practice update in 2019, written by the same lead author as the ESPGHAN guidelines, which says that when a tTG IgA level greater than 10 times the upper limit of normal is combined with a positive EMA antibody in a second blood sample, the positive predictive value for celiac disease is virtually 100 percent and is reliable for diagnosing celiac disease.

The American College of Gastroenterology issued a guideline update at the start of this year. It suggests a combination of high-level tTG IgA (greater than 10 times upper limit of normal) with a positive EMA in a second blood sample as reliable tests for diagnosis of celiac disease in children. “In symptomatic adults unwilling or unable to undergo upper GI endoscopy, the same criteria may be considered after the fact, as a diagnosis of likely CD,” the authors write (Rubio-Tapia A, et al. Am J Gastroenterol. 2023;118[1]:59–76).

At the AACC conference, Dr. Nandakumar presented the following case scenario and asked which test would be best to confirm the diagnosis: A 53-year-old female has symptoms of diarrhea, occasional bloating, and weight loss. She has a history of breast cancer and is six months post-surgery and chemotherapy. She tests positive for tTG IgA (35 U/mL, negative, <3 U/mL). She doesn’t want a biopsy procedure. The best test to confirm the diagnosis of likely celiac disease: anti-endomysial (EMA) IgA.

Assay methods for tTG IgA consist of chemiluminescent, enzyme-linked, and fluorescence enzyme immunoassays and particle-based multianalyte fluorescence platforms. EIA is used in the high-volume ARUP Laboratories, but Dr. Nandakumar and colleagues recently evaluated the Aptiva technology and the clinical performance of the Aptiva system’s anti-tTG IgA assay.

Sera samples from 703 patients were tested for anti-tTG IgA and IgG and for anti-DGP IgA and IgG antibodies on both Quanta Lite EIA and Aptiva platforms. Of the 703 patients, 127 were classified as celiac disease positive (58) and celiac disease negative (69) based on biopsy results. Dr. Nandakumar and coauthors report in their article published in Archives of Pathology & Laboratory Medicine that “anti-tTG IgA detection showed equal clinical sensitivity and specificity of 91% sensitivity and 99% specificity on both platforms.” They add, “Anti-tTG IgG resulted in moderate sensitivity of 69% and 72%, but high specificity of 100% and 94% on Aptiva and Quanta Lite, respectively.”

For anti-DGP IgG, they report sensitivities of 90 percent and 81 percent, and specificities of 94 and 99 percent, on Aptiva and Quanta Lite, respectively. For anti-DGP IgA, they found an 83 percent sensitivity on Quanta Lite and 69 percent on Aptiva, and similar specificities of 97 percent (Quanta Lite) and 98 percent (Aptiva).

They write, “At ≥10 × ULN levels for anti-tTG IgA, Aptiva displayed a sensitivity of 72% and a specificity of 100%, and Quanta Lite showed a sensitivity of 69% and a specificity of 100%.”

Their study, they say, supports the ESPGHAN recommendations for diagnosis of celiac disease in patients with greater than or equal to 10 times the upper limit of normal anti-tTG IgA titers without a biopsy using the Aptiva system. Both Aptiva and Quanta Lite at greater than or equal to 10 times ULN anti-tTG IgA “could be considered for a biopsy-free diagnosis,” they write, when the clinical scenario precludes biopsy, though not in patients with type one diabetes. The patient diagnosed without a biopsy should be monitored “to corroborate the reversal of serology and reconstitution of villi” with the start of a gluten-free diet.

Some patients who do their best to adhere to a gluten-free diet still have symptoms and persistent villous atrophy, Dr. Taylor says. Labcorp in late 2021 introduced a quantitative gluten test for stool samples to monitor patients for diet adherence and accidental gluten consumption and as an aid in assessing refractory celiac disease not related to accidental gluten exposure. “It makes it possible to directly measure the GI disease-triggering source in the patient,” she says.

Areas of future research in celiac disease include a possible relationship between the disease and the gut microbiome—whether changes in the intestinal microbiome play a causal role. “There are papers showing that microbiome signatures differ between people with celiac disease and control participants,” says Dr. Taylor. It raises another question, she says: “Is there a role for probiotics?”

“There are some promising clues, and research is active.”

Research is ongoing into an HLA-DQ-gluten tetramer-based assay to detect gluten-reactive T cells that drive the immune response in people with celiac disease, Dr. Taylor says. The test is designed to measure interleukin-2 release in people on a gluten-free diet after they ingest one bolus of gluten. “People with celiac disease have an increase in IL-2, which distinguishes them from people with non-celiac gluten sensitivity,” she says. The test is not yet available, “but it appears we might be going in that direction.”

The test would be an advance because it could potentially help to diagnose celiac disease in people on a gluten-free diet with no more than a single ingestion of gluten, Dr. Taylor says. Diagnosing celiac disease in such patients is difficult now because it requires a gluten challenge for several weeks, which causes the symptoms to return. “Celiac antibody tests are not reliable as indicators of celiac disease in the context of a gluten-free diet because healing from the diet reduces the antibodies.”

Drs. Lebwohl and Rubio-Tapia in their 2021 article wrote, “If proven accurate and scalable, assays that detect gluten-HLA tetramer complexes might be used in diagnosis to be made in the context of a gluten-free diet without intestinal biopsy.”

For now, Dr. Taylor says, it’s important for all to know celiac disease is underdiagnosed. “Increased awareness will help health care respond to celiac disease and the needs of patients.”

“I see laboratory professionals as educators,” she says.

Valerie Neff Newitt is a writer in Audubon, Pa.