Assumptions about race, differing antibody levels and greater BMI contribute to disparities in testing
By Amy Ratner, director of scientific affairs
Black people in the United States who have celiac disease are at particular risk of being undiagnosed, research from the University of Alabama Birmingham suggests.
“Data have shown that celiac disease is not exclusive to a particular ancestral group,” the study concludes. “People with African ancestry can have celiac disease.”
But physicians’ common view that celiac disease is rare in Black Americans can lead to disparity in testing for the condition, according to the study, published recently as a research letter in the journal, Gastro Hep Advances.
Of 852 people in a registry of potential and confirmed celiac disease patients seen at the university health system over 10 years’ time, nearly 5 percent self-identified as Black. In addition to determining the number of Black people in the registry, researchers set out to identify if there were health-related differences in Black people and non-Hispanic white people.
They found that Black patients with confirmed celiac disease were more likely to have negative results of celiac disease blood tests than non-Hispanic white patients. They were also likely to have significantly higher body mass index (BMI).
Assumptions about race, differing antibody levels and greater BMI could all contribute to disparities in testing and missed opportunities to diagnose celiac disease in Black people, according to the study conducted by Amanda Cartee, MD, a gastroenterologist at the university, and colleagues.
Preliminary results of the study were presented at Digestive Disease Week (DDW) in 2022.
Black people with celiac disease were more likely to have negative but detectable levels of the antibody typically measured in the process of diagnosing celiac disease. Eighty percent of Black patients with biopsy-confirmed celiac disease in the registry had tissue transglutaminase (TTG) Iga test results that were less than the upper limit of normal, compared to about 9 percent of non-Hispanic white patients. A result higher than the upper limit of normal is considered positive.
TTG testing done after patients had already had a biopsy and had started a gluten-free diet and unidentified Iga deficiency are factors that could contribute to negative celiac disease blood tests results, the study says.
Additionally, normal test ranges may vary due to genetic ancestry and sex, study authors wrote, noting that negative blood test results in Black people with confirmed celiac disease need to be further studied in a larger number of patients.
Studies of large groups of people from the general population in the United States have relied heavily on positive blood test results to identify undiagnosed celiac disease, the study says. Consequently, a higher rate of negative blood test results affects diagnosis and further limits understanding of clinical differences in Black patients.
An editorial accompanying the study noted that the diagnostic accuracy of the TTG test in the general population has been called into question by previous research. The new study by Cartee suggests that the TTG test may be a particularly poor screening tool in the Black American population, wrote Isabel Hujoel, MD, a gastroenterologist at the University of Washington Medical Center, who was not involved in the study. She said the practice of relying on TTG to identify cases of celiac disease needs a closer look.
Higher BMI could also play a role in underdiagnosis of Black people because low or normal BMI is expected in classic celiac disease. However, the study found that at diagnosis, Black patients more commonly met the BMI criteria for obesity and white patients for being overweight.
Researchers reviewed billing codes in university medical records from 2011 to 2021. Patients in the registry were categorized as having possible, probable and definite celiac disease based on information used to diagnose celiac disease. This ranged from those on a gluten-free diet without any testing to those who had records of having both blood tests and a biopsy. Overall, there was no statistically significant difference in the percentage of non-Hispanic white and Black people who fell into each subgroup.
Symptoms were the primary reason both non-Hispanic white people and Black people were tested for and diagnosed with celiac disease. Anemia and elevated liver function similarly led to celiac disease testing in both groups.
But osteopenia or osteoporosis, which can be related to celiac disease, led to testing only in white people. Likewise, family history of celiac disease, type 1 diabetes or suspicious results of an endoscopy prompted by something other than celiac disease did not lead to celiac disease testing or diagnosis in Black patients.
In both Black and white patients, clinical guidelines that call for blood tests and subsequent biopsy confirmation were followed only about 50 percent of the time.
In the editorial, Hujoel noted that previous research has indicated that the Black American community has increased rates of adopting a gluten-free diet without a diagnosis of celiac disease. “This raises the possibility that Black Americans with celiac disease are unintentionally self-treating,” she wrote.
Reliance on data from studies based on the percentage of people with antibodies to celiac disease in their blood, called seroprevalence, may underestimate the prevalence in Black people if they are indeed more likely to have normal blood test results, Hujoel explained. The potentially faulty belief that celiac disease has a low prevalence in Black Americans will, in turn, result in fewer endoscopies and biopsies in Black people with suspected celiac disease but normal blood rest results, Hujoel wrote.
“The Black celiac disease community may be caught in a vicious cycle,” she noted.
Up to 80 percent of those with celiac disease remain undiagnosed. The likelihood of being diagnosed could be influenced by race and ethnicity because of access to medical care, referral bias and other factors.
Beyond Celiac research that shows one in three patients who screen positive for celiac disease never go on to get a biopsy to confirm diagnosis, with disparities driven by gender, age and race, has been selected to be presented as a poster at DDW 2024. The research is based on an analysis of private insurance healthcare claims.
Additionally, Beyond Celiac has partnered with the National Minority Quality Forum (NMQF) to examine and address health inequities in the diagnosis and treatment of celiac disease. The joint project aims to increase awareness of the prevalence of celiac disease in the United States and to investigate the extent of undiagnosed celiac disease in diverse populations.
Earlier this year, a study by a Columbia University researcher based on the analysis of data compiled by Beyond Celiac and NMQF was published as a research letter in the American Journal of Gastroenterology. The study, which looked at Medicare claims data, found that a higher income, living in an urban area and living close to a celiac disease center are all positively correlated with celiac disease prevalence, while being Black or Latino/Hispanic is negatively correlated.
You can read more about the University of Alabama study here.
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