In this study, we provide evidence that antibody tests are more reliably predicting mucosal status in children with CD before than in children after prescription of a GFD.
In our patients, according to AUCs (Figure 2), TG2-IgA, DPG-IgG and DPG-IgA antibody tests performed very well in diagnosing CD in group A, similar to the performances reported elsewhere . However, when used for monitoring mucosal status in CD after a median of 2.2 years after primary diagnosis (group B), all tests suffered a performance loss turning out to be significant in case of DPG-IgA. According to LRs, additional parameters quantifying the non-invasive tests' performance, TG2-IgA, DGP-IgG and -IgA antibodies were most informative and clinically useful with respect to diagnosing CD in group A. Conversely, the limited ability to detect mucosal injury in group B was reflected by LRs + in all tests being < 10. Regarding LRs-, only negative EMA had an LR- < 0.1 thus being an informative and clinically useful marker of mucosal healing in CD .
Positive EMA, however, were detected in 18 children from group B. Twelve of these EMA-positive children showed mucosal healing, a finding that reflects faster mucosal recovery than EMA-seroconversion. Indeed, EMA-positive children exhibiting mucosal healing had been on the GFD for a significantly shorter period of time than the EMA-negative children. Moreover, 9 of 12 developed EMA-negativity on further follow-up. This delayed seroconversion might partially explain positive EMA in subjects showing mucosal healing . However, adherence to the dietary treatment was not evaluated in this study nor was small intestinal mucosa examined for IgA deposits . Therefore, we cannot rule out that serum EMA-positivity is more sensitive than gross histological damage to detect minor dietary transgressions. Positive EMA without histological evidence of CD were also detected in 3 children from group A2. EMA normalized on a normal gluten-containing diet in 2 of the EMA-positive group B children while the third became seronegative on a self-prescribed GFD and stayed seronegative even after a 11-month gluten challenge. However, since EMA is a very strong predictor of a subsequent CD diagnosis , there is need of further follow-up in these children including endoscopy.
All the children participating in the study underwent EGD as criterion standard for the evaluation of the diagnostic reliability of the antibody tests. In the light of the possibility to diagnose CD without biopsies , an important finding of our study was that experiences with the diagnostic biopsy did not deter two thirds of the children eligible for group B from undergoing re-biopsy. We found mucosal healing in the majority of the re-biopsied children, 90% of them had Marsh < 2. All group B children with mucosal injury were ≥ 9 years old and belonged to the subgroup that had been on a GFD < 2 years. In children, the long-term mucosal healing rate was reported to be 100% and histological recovery might even occur after more than 2 years after primary diagnosis . In contrast, it has been shown that children diagnosed after the age of 4 tend to follow the GFD less strictly and therefore are expected to have a higher prevalence of mucosal injury . Surprisingly, a very low frequency (1.8%) of isolated increase of intraepithelial lymphocyte count (Marsh 1) was found among group B children. This finding could be related to the somewhat high cut-off for an increased intraepithelial lymphocyte count used in the study (≥ 30 lymphocytes/100 epithelial cells).
This study has several strengths. In the first place, it was conducted in children. Concerning the correlation between follow-up histology and serology, most of the studies investigating this correlation were conducted in adults [2, 3, 8, 9, 11, 24–27]. However, in one pediatric study on the value of DGP-antibodies in the follow-up of CD, only 13 children had both re-endoscopy and follow-up serology . Another study with children is of limited value in the aspect that only seroconverted children were included . Then, in contrast to the current study, most of the studies reporting on correlations between follow-up histology and serologies are retrospective [2, 26, 28, 29]. Another strength of the current study was the cut-off point being adjusted for the study population in case of all antibody tests according to ROC analysis (Table 1). This adjustment is especially important in children since manufacturers’ cut-offs are usually based on data from adults. A further advantage was the use of AUCs. AUCs as effective single indicators of the agreement between a test and a reference standard facilitate the comparison of the overall performance between different non-invasive diagnostic tests [15, 16]. Additionally, in order to increase the reliability of the reference standard, two pathologists, before reaching a consensus diagnosis, independently reviewed all biopsy samples, which had been taken according to guidelines [7, 30, 31]. Furthermore, we were able to systematically examine all recommended serologic tests. In contrast to recent recommendations for the use of DGP-IgA in monitoring treated CD , we found that DGP-IgA suffered a significant performance loss when used for follow-up in children. We therefore consider DGP-IgA less reliable for follow-up purposes compared with EMA, TG2-IgA and DGP-IgG. For the comparisons regarding the performance loss of the serologic tests other than DGP-IgA, mean empirical power was rather low, a finding we consider an important limitation of this study. Therefore, future research is needed to further clarify the correlation of EMA, TG2-IgA and DGP-IgG with follow-up histology or identify other reliable non-invasive follow-up tests in CD.