Fully-automated, chemiluminescence IgA and IgG anti-tissue transglutaminase (tTG) antibodies serum assays for the screening of celiac disease

Diagnostic Accuracy of IgA Anti-Transglutaminase Assessed by Chemiluminescence: A Systematic Review and Meta-Analysis

A new chemiluminescence immunoassay method (CLIA) for detecting IgA anti-transglutaminase (atTG IgA) in celiac disease (CD) has prompted inquiries into its diagnostic performance. We conducted a systematic review and meta-analysis comparing CLIA with traditional enzyme-linked immunosorbent assay (ELISA) and fluorescence enzyme immunoassay (FEIA). We searched PubMed, Medline, and Embase databases up to March 2024. The diagnostic references were intestinal biopsy and ESPGHAN guidelines. We calculated the sensitivity and specificity of atTG IgA assessed by CLIA and the odds ratio (OR) between the assays. Eleven articles were eligible for the systematic review and seven for the meta-analysis. Sensitivity and specificity of atTG IgA CLIA-assay were 0.98 (95% CI, 0.95-0.99) and 0.97 (95% CI, 0.94-0.99), respectively. The sensitivity of atTG IgA antibody detection did not significantly vary across the three assay modalities examined (CLIA vs. ELISA OR: 1.08 (95% CI, 0.56-2.11; p = 0.8); CLIA vs. FEIA OR: 6.97 (95% CI, 0.60-81.03; p = 0.1). The specificity of atTG IgA assessed by FEIA was higher than for CLIA (OR 0.17 (95% CI, 0.05-0.62); p < 0.007). According to the systematic review, normalization of atTG IgA levels in CD patients following a gluten-free diet was delayed when using CLIA compared to ELISA and FEIA methods. Conflicting findings were reported on the antibody threshold to use in order to avoid biopsy confirmation.

Positive tissue transglutaminase antibodies with negative endomysial antibodies: Unresolved issues in diagnosing celiac disease

BACKGROUND

The serological screening for celiac disease (CD) is currently based on the detection of anti-transglutaminase (tTG) IgA antibodies, subsequently confirmed by positive endomysial antibodies (EMA). When an anti-tTG IgA positive/EMA IgA negative result occurs, it can be due either to the lower sensitivity of the EMA test or to the lower specificity of the anti-tTG test. This study aimed at verifying how variation in analytical specificity among different anti-tTG methods could account for this discrepancy.

METHODS

A total of 130 consecutive anti-tTG IgA positive/EMA negative samples were collected from the local screening routine and tested using five anti-tTG IgA commercial assays: two chemiluminescence methods, one fluoroimmunoenzymatic method, one immunoenzymatic method and one multiplex flow immunoassay method.

RESULTS

Twenty three/130 (17.7%) patients were diagnosed with CD. In the other 107 cases a diagnosis of CD was not confirmed. The overall agreement among the five anti-tTG methods ranged from 28.5% to 77.7%. CD condition was more likely linked to the positivity of more than one anti-tTG IgA assay (monopositive = 2.5%, positive with ≥ three methods = 29.5%; p = 0.0004), but it was not related to anti-tTG IgA antibody levels (either positive or borderline; p = 0.5).

CONCLUSIONS

Patients with positive anti-tTG/negative EMA have a low probability of being affected by CD. Given the high variability among methods to measure anti-tTG IgA antibodies, anti-tTG-positive/EMA-negative result must be considered with extreme caution. It is advisable that the laboratory report comments on any discordant results, suggesting to consider the data in the proper clinical context and to refer the patient to a CD reference center for prolonged follow up.

Celiac Disease in Patients With Cystic Fibrosis on Ivacaftor: A Case Series

Cystic fibrosis transmembrane conductance regulator (CFTR) protein modulators have revolutionized care for individuals with cystic fibrosis (CF) with positive effects on the gastrointestinal (GI) tract. There is emerging evidence linking CFTR dysfunction to celiac disease (CD). We present 3 cases of patients with CF, genotype F508del/G551D, treated with CFTR modulator, ivacaftor, and diagnosed with CD. These patients tested for CD because they had persistent GI symptoms that had partially improved with ivacaftor. This case series highlights the importance of a better understanding of how CFTR modulators impact the GI tract, their possible link to CD, and the importance of considering CD when evaluating GI symptoms in individuals with CF.

Trend of Antitissue Transglutaminase Antibody Normalization in Children With Celiac Disease Started on Gluten-free Diet: A Comparative Study Between Chemiluminescence and ELISA Serum Assays

BACKGROUND

The aim of this study is to compare the performance of antitissue transglutaminase (atTG) chemiluminescence immunoassay (CLIA) with the standard enzyme-linked immunosorbent assay (ELISA) methods in monitoring celiac children after the start of gluten-free diet (GFD).

METHODS

Celiac children diagnosed between 2005 and 2016 at our centre were classified into 2 groups based on serum assay (ELISA vs CLIA) used for atTG monitoring, and were compared on percentage of decrease and time to normalization of atTG on GFD.

RESULTS

Among 260 included children, the rate of normalization of atTG levels at 30 months' follow-up was 86% and 70% in ELISA and CLIA group, respectively (P < 0.01). Median time to normalization was 11.7 and 14.7 months in ELISA and CLIA group respectively (P = 0.003). Marsh score at diagnosis was not associated with time to atTG normalization (P = 0.770), whereas older age at diagnosis and higher baseline atTG predicted longer time to atTG normalization (P = 0.01, P < 0.01).

CONCLUSIONS

The percentage and the time of the atTG normalization in celiac children on GFD should be interpreted according to the utilized assay: at 30 months' follow-up children tested by CLIA are less likely to normalize atTG levels compared to those tested by ELISA. Younger age at diagnosis and lower baseline atTG are predictors of earlier atTG normalization, regardless of the adopted assay.

Celiac Disease Diagnosis Without Biopsy: Is a 10× ULN Antitransglutaminase Result Suitable for a Chemiluminescence Method?

OBJECTIVES

2012 European Society of Pediatric Gastroenterology, Hepatology and Nutrition guidelines allow to establish a celiac disease diagnosis without duodenal biopsy in symptomatic pediatric patients with antitissue transglutaminase (anti-tTG) titers >10 times the upper limit of normal. For some years now, new chemiluminescence immunoassays have been made available: it is important to establish the clinical performance of anti-tTG and to determine the cut-off best suited to predict Marsh ≥2 to avoid gastrointestinal endoscopy not only in children, but also in the adult population.

METHODS

A total of 2565 patients performed duodenal biopsy from July 2012 to September 2016; we selected all the patients who had undergone QUANTA Flash anti-tTG immunoglobulin A (IgA) within -3 months of duodenal biopsy and before the start of gluten-free diet. A total of 827 patients fulfilled the criteria for selection.

RESULTS

Using a cut-off of 20 chemiluminescent unit (CU; area under the curve: 0.995), sensitivity, specificity, positive, and negative predictive value were 98.2%, 98.4%, 97.9%, and 98.6%, respectively. For the correlation with Marsh ≥2, in the pediatric population, positive predictive values (PPV) were 92.1%, 99%, and 100% at 200 CU (10×), 560 CU (28×), and 1000 CU (50×), respectively. In the adult population PPV was 94.2%, 98.2%, and 100% at 200 CU (10×), 350 CU (15×), and 400 CU (20×).

CONCLUSIONS

Sensitivity, specificity, positive, and negative predictive value of QUANTA Flash h-tTG IgA were excellent. The cut-off providing an optimized PPV for histological lesions compatible for celiac disease (Marsh ≥2) for the QUANTA Flash h-tTG IgA is 350 CU (15×) in adult and 560 CU (28×) in children.

Hemolysis and IgA-antibodies against tissue transglutaminase: When are antibody test results no longer reliable?

BACKGROUND

Antibodies against tissue transglutaminase (TTG) of isotype IgA (IgA-aTTG) represent reliable diagnostic markers to confirm or exclude celiac disease (CD). Hemolysis (HL) is an important pre-analytical factor. HL can be quantified as HL index (HI) correlating with the concentration of free hemoglobin. TTG is abundant in erythrocytes and released upon HL. In immunoassays, the released TTG may interfere with binding of IgA-aTTG to the coated TTG.

METHODS

We selected 17 HL-free sera from children with biopsy-confirmed CD: 7 with low-positive (1-5 multiples of upper limit of normal [×ULN]), 5 with intermediate (5-10 × ULN) and 5 with high IgA-aTTG (10-15 × ULN). Sera were spiked with hemolysates resulting in HIs ranging from 12.5 to 800 (12.5-800 mg/dL free hemoglobin).

RESULTS

IgA-aTTG values were significantly decreased (>10%) after addition of hemolysates even if HL was invisible (HI <50). This effect is diagnosis-relevant if IgA-aTTG values are measured just below the cut-offs: (i) 0.4-1 × ULN at HI ≥25 (CD not excludable) and (ii) 8.5-10 × ULN at HI ≥200 (diagnosis of CD without biopsy not possible). Antibodies against deamidated gliadin were not influenced by HL.

CONCLUSIONS

IgA-aTTG results in sera with HI ≥25 can yield inconclusive results. Therefore, those antibody results should be assessed only under consideration of the HI.