This population-based prospective cohort study shows that: (1) Serum TG2A screening at 6 years of age in the healthy childhood population has a positive predictive value of 61% to detect subclinical CD. (2) The level of serum TG2A in subclinical CD is not predictive for the severity of enteropathy.
Although we followed the ESPGHAN guideline for CD diagnosis in the majority of asymptomatic children, the PPV of TG2A screening may still have been influenced by misclassification of the outcome. According to the Oslo definitions [
10],
potential CD refers to children who are at increased risk of developing CD as indicated by positive serology, but with a
normal small intestinal bowel mucosa. In our study, 23 children were considered to have
subclinical CD on the basis of the combination of positive TG2A and the presence of enteropathy. However, five CD cases did not consent for GI endoscopy, thus we lacked formal proof for diagnosis of CD. Still, three of them had elevated levels >10 ULN, and they were all EmA and HLA DQ2 or 8 positive, suggesting that enteropathy is highly likely. Therefore, excluding these children would likely result in underdiagnosis. Second, loss to follow-up might have affected the precision of the PPV of TG2A screening. If children who were lost to follow-up (
n = 8) would not have CD, then the initial PPV of screening on TG2A would have been 31/59 (53%). In contrast, if all children who were lost would be CD cases, then the PPV would have been 39/59 (66%) Thus, the positive predictive value of serum TG2A screening to detect subclinical CD in the general childhood population would be maximally 66%.
In contrast with several other studies, we did not find a positive association between serum TG2A levels and the degree of enteropathy [
16,
21,
31‐
33]. However, these previous studies concerned children with gastrointestinal symptoms that triggered CD testing, and contrast our cases of subclinical CD, complicating a direct comparison between studies. In fact, it has been shown that TG2A levels are more strongly correlated with the severity of intestinal lesions in symptomatic patients, than in asymptomatic children [
21]. Hence, the association between TG2A levels and the degree of enteropathy might be differentially influenced by the presence -or lack- of symptoms. In our study, the majority of children with high TG2A levels mentioned gastrointestinal symptoms. According to the ESPGHAN guideline, biopsies could have been omitted in this group. However, on the basis of the present study, it needs to be considered that children with TG2A ≥10 ULN in most cases needed a biopsy to confirm CD. Moreover, our results confirm that the presence and severity of gastrointestinal symptoms, such as abdominal pain, are insufficient to discriminate subclinical CD cases from healthy children [
34]. The majority (90%) of children who did not develop CD mentioned gastrointestinal symptoms as well, such as abdominal pain, constipation, diarrhea, nausea, or fatigue. Gastrointestinal symptoms were also not related to the degree of enteropathy, nor TG2A levels. Nonetheless, consistent with our previous findings [
25], subclinical children weighed less than healthy children. Interestingly, the TEDDY study demonstrated that the majority of subclinical children had normal weight and height growth at age 4 [
21], which may suggest that the deviation in height and weight growth becomes more prominent between 4 and 6 years of age, and appears before gastrointestinal symptoms occur. Hence, increased clinical vigilance focusing on weight growth parameters, especially BMI [
35], or systematic growth monitoring in the general pediatric population, might improve early detection of CD [
36]. Nevertheless, the effects of early diagnosis, and the benefit of treatment with a gluten-free diet of subclinical patients, needs to be further studied. In the short run, symptoms that may -or may not- have been recognized upon the start of a GFD may disappear, serving as a proof to parents [
37], but evidence in children is lacking. In addition, the benefits and cost-effectiveness of screening in asymptomatic individuals remains controversial [
38‐
40]. Introducing a screening test in the general pediatric population with a positive predictive value of 61% to diagnose a disease with lifelong consequences (such as a gluten-free diet, regular health care visits, screening for other diseases, screening and investigating family members, fear of complications, and economic burden from the gluten-free diet) may not be reasonable. Therefore, it would be too premature to recommend screening in the general pediatric population.
Methodological considerations
The premise of the study was the identification of CD in asymptomatic children. Three children in our study developed symptoms following screening, thereby triggering CD diagnosis in routine clinical practice. One of the strengths of our study is that we used a prospective study design, with a similar protocol for the diagnostic process for all screened TG2A-positive children. Furthermore, all screened TG2A-positive children were of the same age, and analyzed 3 years later by the same laboratory and same test kit. Because all participants were unaware of TG2A determination, we were able to study the development of TG2A levels over 3 years of time. Ten children with negative TG2A did not have CD, despite TG2A positivity at 6 years of age. Explanations for the contradictory test results at 6 and 9 years may be that TG2A levels were transiently high at 6 years, test results at 6 years were false positive (i.e., 1-specificity), or gluten intake decreased over time. Intriguingly, on top of the 1.4% of children with positive TG2A levels at 6 years of age (of whom 61% received a subclinical CD diagnosis), 0.2% of TG2A negative children developed CD within 3 years after the negative TG2A screening result at 6 years of age. The median age of retesting was 9.9 years, with a range between 8.4 and 11.4 years. This large age range is related to the inclusion period of 2.5 years. Another strength of our study is that TG2A measurements were performed in combination with assessment of EMA, genetic risk types, and biopsy specimens at the same time of second serology assessment. Last, all biopsies were evaluated by expert pathologists by using the Marsh–Oberhuber criteria to classify the degree of enteropathy. Nevertheless, several limitations should be taken into account as well. First of all, five children in the CD group were considered to have subclinical CD without biopsy results. Therefore, we did not fully meet the ESPGHAN criteria for CD diagnosis. However, three of them had levels exceeding 10 ULN, they were all EMA positive, and carried the genetic risk type. Hence, CD diagnosis is highly likely. Second, symptoms were assessed only among those with TG2A positivity at 9 years of age, after parents were informed about the initial screening TG2A status, which might have induced bias. However, the presence of gastrointestinal symptoms was evaluated systematically during routine clinical evaluation, preceding second serological (TG2A) assessment, additional EMA assessment, genetic risk typing, and gastrointestinal endoscopies at 9 years of age. Hence, symptom assessment was independent of the outcome, making bias less likely. Furthermore, symptoms were assessed by one experienced gastroenterologist minimizing inter-observer bias. We did not specifically ask for the presence of joint pains or neurological symptoms, but these complaints were not reported on the general question “any complaints”. Hence, the occurrence of joint pains and neurological symptoms seems unlikely.