Systematic Review With Meta-analysis

The Accuracy of Serological Tests to Support the Diagnosis of Coeliac Disease

Athena L. Sheppard; Martha M. C. Elwenspoek; Lauren J. Scott; Victoria Corfield; Hazel Everitt; Peter M. Gillett; Alastair D. Hay; Hayley E. Jones; Susan Mallett; Jessica Watson; Penny F. Whiting

Disclosures

Aliment Pharmacol Ther. 2022;55(5):514-527.

Abstract and Introduction

Abstract

Background: There is growing support for a biopsy avoidant approach to diagnose coeliac disease in both children and adults, using a serological diagnosis instead.

Aims: To assess the diagnostic accuracy of serological tests for coeliac disease in adults and children.

Methods: Seven electronic databases were searched between January 1990 and August 2020. Eligible diagnostic studies evaluated the accuracy of serological tests for coeliac disease against duodenal biopsy. Risk of bias assessment was performed using QUADAS-2. Bivariate random-effects meta-analyses were used to estimate serology sensitivity and specificity at the most commonly reported thresholds.

Results:113 studies (n = 28,338) were included, all in secondary care populations. A subset of studies were included in meta-analyses due to variations in diagnostic thresholds. Summary sensitivity and specificity of immunoglobulin A (IgA) anti-tissue transglutaminase were 90.7% (95% confidence interval: 87.3%, 93.2%) and 87.4% (84.4%, 90.0%) in adults (5 studies) and 97.7% (91.0%, 99.4%) and 70.2% (39.3%, 89.6%) in children (6 studies); and of IgA endomysial antibodies were 88.0% (75.2%, 94.7%) and 99.6% (92.3%, 100%) in adults (5 studies) and 94.5% (88.9%, 97.3%) and 93.8% (85.2%, 97.5%) in children (5 studies).

Conclusions: Anti-tissue transglutaminase sensitivity appears to be sufficient to rule out coeliac disease in children. The high specificity of endomysial antibody in adults supports its use to rule in coeliac disease. This evidence underpins the current development of clinical guidelines for a serological diagnosis of coeliac disease. Studies in primary care are needed to evaluate serological testing strategies in this setting.

Introduction

Coeliac disease is a chronic small intestinal immune-mediated enteropathy triggered by the ingestion of gluten, a protein found in wheat, rye and barley.^[1] Exposure to gluten results in intestinal damage of varying severity in patients affected by coeliac disease. Symptomatic coeliac disease is characterised by gastrointestinal symptoms, including diarrhoea, nausea, vomiting and abdominal pain, and extraintestinal symptoms such as fatigue and weight loss.

Coeliac disease is estimated to affect around 1% of people in the UK,^[2] however only 24% of those with coeliac disease are thought to be diagnosed.^[3] These large numbers of undiagnosed patients—known as the "coeliac iceberg"—are thought to be a consequence of the non-specific nature of coeliac disease symptoms and variation in clinical presentation, from none (asymptomatic coeliac disease) to a broad spectrum of symptoms.^[1] People with certain health conditions, such as type I diabetes, autoimmune thyroid disease or Down syndrome, as well as first-degree relatives of people with coeliac disease, are at higher risk of developing coeliac disease than the general population and are more likely to present without classical symptoms.^[4]

Currently, the only treatment for coeliac disease is lifetime adherence to a gluten-free diet, which is expensive and can be difficult to comply with. Left undiagnosed and untreated, coeliac disease often leaves patients with troublesome symptoms that significantly affect their quality of life and lead to a higher risk of complications such as osteoporosis, infertility and small bowel cancer.^[5] As such, a timely and accurate diagnosis of coeliac disease is important.

Coeliac disease is diagnosed using a combination of serological tests for coeliac-specific antibodies and endoscopic intestinal biopsy. Current guidelines by the National Institute for Health and Care Excellence recommend both adults and children with suspected coeliac disease first undergo serological testing for total immunoglobulin A (IgA) and IgA anti-tissue transglutaminase (tTG).^[4] In IgA deficient patients, immunoglobulin G (IgG) endomysial antibodies (EMA), IgG deamidated gliadin peptide (DGP) or IgG tTG can be used. In adults, weakly positive for IgA tTG, IgA EMA should be measured. Seropositive adults should be referred for intestinal biopsy, while seropositive children should be referred for further investigation, which may include intestinal biopsy, IgA EMA, human leukocyte antigen (HLA) genetic testing, or a combination of the above.^[4]

Intestinal biopsy is invasive and can be burdensome for patients, particularly children, who require general anaesthesia to undergo the procedure. Patients must consume a gluten-containing diet for at least six weeks prior to any serological test or biopsy, meaning those with coeliac disease may continue to experience painful and debilitating symptoms while they wait. Guidelines in the UK have begun to move towards biopsy-avoidance strategies for coeliac disease in children and, more recently, in adults. In their 2013 guidelines, the British Society of Paediatric Gastroenterology, Hepatology and Nutrition advised that children with IgA tTG greater than or equal to 10x the upper limit of normal for the assay, positive for IgA EMA and HLA positive do not need to undergo biopsy to confirm their coeliac disease diagnosis.^[6] During the coronavirus pandemic, the British Society of Gastroenterology published interim guidance including a COVID-19 specific non-biopsy protocol for adults with suspected coeliac disease.^[7]

Previous systematic reviews of the accuracy of serological testing for diagnosing coeliac disease suggest that the tests are highly sensitive and specific in both adults and children.^[8–12] These systematic reviews, however, are all out-of-date and most have methodological limitations. Limitations included: limited search;^[8–11] use of the Moses-Littenberg model^[13] to pool estimates of sensitivity and specificity rather than the more robust bivariate or hierarchical summary receiver operating characteristic (HSROC) models^[14,15] or no statistical synthesis of results;^[10] and use of the original QUADAS-tool^[16] to assess study quality (although at the time this was the most appropriate tool) the results of which were then not incorporated into the synthesis,^[8,9,11] or no quality assessment.^[10] The most recent, comprehensive review by Maglione et al, conducted for the AHRQ programme, was the only review to include more than 20 studies.^[12] However, this review also included existing systematic reviews and only generated overall summary estimates for studies published since existing reviews; it did not produce overall estimates of the accuracy of the included serological tests. This review was restricted to studies that either included at least 300 participants or were conducted in an "at risk" population—reasons for the sample size restriction were not justified. None of the reviews considered the study threshold when calculating pooled estimates of sensitivity and specificity.

The purpose of this systematic review is to provide a robust and up-to-date evaluation of the accuracy of serological tests for coeliac disease in adults and children.

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Next Section

Abstract and Introduction
Materials and Methods
Results
Discussion
References

Table 1. Study estimates of test accuracy, stratified by age group and test
Serological test	Studies, n	Participants (coeliac disease), n	Threshold	Sensitivity (range), %	Specificity (range), %
All data
Adults
IgA tTG	27	11 355 (2566)	5–25 U/mL	35.2–100.0	0.0–100.0
IgG tTG	1	65 (14)	10 U/mL	71.4	96.1
IgA EMA	19	7122 (1028)	1:5–1:20	61.3–100.0	87.5–100.0
IgG EMA	1	96 (28)	1:20	39.3	98.5
IgA DGP	3	885 (154)	10–20 U/mL	85.7–98.3	92.2–95.7
IgG DGP	4	1046 (217)	10–20 U/mL	90.0–96.7	99.2–100.0
IgA/IgG DGP	4	1161 (280)	20 U/mL	86.2–98.3	95.9–98.8
IgA/IgG tTG/DGP	3	1849 (173)	20 U/mL	72.2–96.3	80.4–97.4
IgA AAA	2	820 (140)	25 U/mL	80.0, 86.7	92.2, 95.1
Children
IgA tTG	37	7944 (4164)	3–100 U/mL	28.6–100.0	7.9–100.0
IgG tTG	5	599 (278)	3, 7 U/mL	31.0–97.4	70.8–100.0
IgA/IgG tTG	2	742 (282)	6, 45.1 U/mL	94.4, 96.0	85.8, 99.5
IgA EMA	28	4974 (2472)	1:5–1:40	40.0–100.0	29.4–100.0
IgA/IgG EMA	2	173 (131)	1:2.5, 1:5	95.3, 95.7	74.2, 90.9
IgA DGP	1	212 (109)	20 U/mL	85.3	88.3
IgG DGP	3	1135 (669)	10–25 U/mL	77.2–92.0	83.5–94.1
IgA/IgG DGP	6	941 (464)	16–20 U/mL	87.5–100.0	22.2–96.4
IgA/IgG tTG/DGP	4	986 (415)	3–32.7 U/mL	87.5–98.2	61.2–99.5
Mixed or unspecified
IgA tTG	25	4564 (1414)	2–89.5 U/mL	38.1–100.0	9.5–100.0
IgG tTG	2	432 (122)	10, 18.9 U/mL	40.6, 84.6	78.0, 89.0
IgA/IgG tTG	1	254 (26)	7.8 U/mL	92.3	82.9
IgA EMA	15	2884 (843)	1:2.5–1:10	68.0–100.0	38.9–100.0
IgA DGP	2	561 (58)	19.9 U/mL	77.1, 90.0	93.4, 96.6
IgG DGP	2	562 (56)	19.9 U/mL	76.1, 80.0	92.0, 99.2
IgA/IgG DGP	3	480 (48)	NR	70.6–85.7	92.9–98.7
IgA AAA	1	391 (10)	NR	50	91.3

Abbreviations: AAA, anti-actin antibodies; DGP, deamidated gliadin peptide; EMA, endomysial antibodies; IgA, immunoglobulin A; IgG, immunoglobulin G; NR, not reported; tTG, anti-tissue transglutaminase.

Table 2. Summary estimates of sensitivity, specificity and likelihood ratios, restricted to the most commonly reported threshold only
Serological test	Studies, n	Participants (coeliac disease), n	Threshold	Sensitivity (95% CI), %	Specificity (95% CI), %	Positive likelihood ratio (95% CI)	Inverse negative likelihood ratio (95% CI)
Most common threshold
Adults
IgA tTG	5	4310 (454)	15 U/mL	90.7 (87.3, 93.2)	87.4 (84.4, 90.0)	7.2 (5.8, 9.1)	9.4 (6.8, 12.8)
IgA EMA	5	927 (446)	1:05	88.0 (75.2, 94.7)	99.6 (92.3, 100.0)	340.7 (12.2, 9539.8)	7.6 (3.9, 14.7)
IgA DGP^†	2	820 (140)	20 U/mL	96.4 (91.7, 98.5)	95.4 (93.6, 96.8)	21.2 (15.0, 29.9)	26.7 (11.3, 63.2)
IgG DGP^†	3	981 (203)	20 U/mL	93.6 (88.6, 96.5)	99.4 (98.5, 99.7)	145.7 (60.8, 349.4)	15.6 (8.6, 28.3)
IgA/IgG DGP	4	1161 (280)	20 U/mL	91.5 (84.7, 95.4)	96.7 (95.3, 97.7)	27.7 (19.0, 40.5)	11.4 (6.2, 20.9)
IgA/IgG tTG/DGP^†	2	851 (155)	20 U/mL	93.5 (88.4, 96.5)	86.3 (79.7, 91.0)	6.8 (4.5, 10.3)	13.4 (7.3, 24.5)
IgA AAA^†	2	820 (140)	25 U/mL	82.9 (75.7, 88.2)	92.5 (90.3, 94.3)	11.0 (8.4, 14.5)	5.4 (3.7, 7.8)
Children
IgA tTG	6	2232 (1051)	20 U/mL	97.7 (91.0, 99.4)	70.2 (39.3, 89.6)	3.3 (1.3, 8.0)	30.4 (8.5, 108.7)
IgA EMA	5	1257 (685)	1:10	94.5 (88.9, 97.3)	93.8 (85.2, 97.5)	11.2 (3.3, 37.4)	14.8 (7.7, 28.2)
IgA/IgG DGP	5	533 (276)	20 U/mL	96.4 (91.7, 98.5)	77.4 (44.0, 93.7)	4.3 (1.4, 13.1)	21.5 (10.7, 43.4)
IgA/IgG tTG/DGP^†	2	244 (133)	20 U/mL	95.6 (83.9, 98.9)	62.2 (52.8, 70.7)	2.5 (2.0, 3.2)	14.3 (3.6, 57.0)

Abbreviations: AAA, anti-actin antibodies; CI, confidence interval; DGP, deamidated gliadin peptide; EMA, endomysial antibodies; IgA, immunoglobulin A; IgG, immunoglobulin G; tTG, anti-tissue transglutaminase.
^†Univariate fixed-effect meta-analysis.

Table 3. Study estimates of sensitivity and specificity limited to specific subgroups, stratified by age group and test
Serological test	Studies, n	Participants (coeliac disease), n	Threshold	Sensitivity (range), %	Specificity (range), %
Symptomatic patients only
Adults
IgA tTG	7	4244 (325)	5–20 U/mL	64.3–100.0	88.2–98.1
IgA EMA	8	3786 (327)	1:5–1:20	61.3–100.0	98.1–100.0
Children
IgA tTG	8	1126 (615)	4–20 U/mL	40.0–100.0	7.9–100.0
IgA EMA	8	1327 (753)	1:5–1:20	40.0–97.6	42.9–100.0
All patients underwent biopsy
Adults
IgA tTG	26	11 183 (2444)	5–25 U/mL	64.3–100.0	0.0–100.0
IgA EMA	18	7010 (1021)	1:5–1:20	61.3–100.0	87.5–100.0
Children
IgA tTG	31	5824 (3330)	3–100 U/mL	28.6–100.0	23.5–100.0
IgA EMA	22	3685 (2015)	1:5–1:40	45.8–100.0	29.4–100.0
Low risk of bias
Adults
IgA tTG	5	1577 (426)	5–20 U/mL	76.0–100.0	87.5–98.3
IgA EMA	2	268 (103)	1:5, 1:20	61.3, 89.3	100.0, 100.0
Children
IgA tTG	4	1319 (823)	20–21 U/mL	94.8–100.0	23.5–98.7
IgA EMA	1	873 (528)	1:10	95.3	94.2

Abbreviations: EMA, endomysial antibodies; IgA, immunoglobulin A; tTG, anti-tissue transglutaminase.

Table 4. Study estimates of sensitivity and specificity, restricted to comparative studies only
Serological test	Studies, n	Participants (coeliac disease), n	Threshold	Sensitivity (range), %	Relative sensitivity (range), %	Specificity (range), %	Relative specificity (range), %
Comparative data
Adults
IgA tTG vs IgA EMA	14	6575 (881)
IgA tTG			5–25 U/mL	64.3–100.0		81.3–99.1
IgA EMA			1:05	61.3–100.0	0.81–1.22	87.5–100.0	1.00–1.17
IgA tTG vs IgA DGP	3	885 (154)
IgA tTG			10–20 U/mL	64.3–95.0		88.2–97.5
IgA DGP			10–20 U/mL	85.7–98.3	1.04–1.33	92.2–95.7	0.96–1.04
IgA tTG vs IgG DGP	4	1046 (217)
IgA tTG			10–20 U/mL	64.3–95.2		88.2–98.0
IgG DGP			10–20 U/mL	90.0–96.7	0.99–1.44	99.2–100.0	1.02–1.13
IgA tTG vs IgA/IgG DGP	4	1161 (280)
IgA tTG			5–20 U/mL	76.0–95.0		94.8–99.0
IgA/IgG DGP			20 U/mL	86.2–98.3	1.01–1.14	95.9–98.8	0.99–1.01
Children
IgA tTG vs IgA EMA	16	3021 (1746)
IgA tTG			5.5–21 U/mL	28.6–99.0		23.5–100.0
IgA EMA			1:5–1:10	50.0–100.0	0.91–2.25	29.4–100.0	0.76–1.25

Abbreviations: DGP, deamidated gliadin peptide; EMA, endomysial antibodies; IgA, immunoglobulin A; IgG, immunoglobulin G; tTG, anti-tissue transglutaminase.

Authors and Disclosures

Athena L. Sheppard^1,2, Martha M. C. Elwenspoek^1,2, Lauren J. Scott^1,2, Victoria Corfield², Hazel Everitt³, Peter M. Gillett⁴, Alastair D. Hay², Hayley E. Jones², Susan Mallett⁵, Jessica Watson² and Penny F. Whiting²

¹The National Institute for Health Research Applied Research Collaboration West (NIHR ARC West) at University Hospitals Bristol NHS Foundation Trust, Bristol, UK
²Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
³Primary Care Research Centre, Faculty of Medicine, University of Southampton, Southampton, UK
⁴Paediatric Gastroenterology Department, Royal Hospital for Children and Young People, Edinburgh, UK
⁵Centre for Medical Imaging, University College London, London, UK

Correspondence
Athena L. Sheppard, Swansea University Medical School, Swansea University, Swansea, UK. Email: 2138248@swansea.ac.uk

Author contributions
Conceptualisation: ALS, MMCE, LJS, VC, HE, PMG, HEJ, JW, PFW. Data curation: ALS, MMCE, LJS, VC. Formal analysis: ALS, MMCE, LJS, HE, PMG, ADH, HEJ, SM, JW, PFW. Funding acquisition: PFW. Investigation: ALS, MMCE, LJS, HE, PMG, ADH, HEJ, SM, JW, PFW. Methodology: ALS, MMCE, LJS, HE, PMG, ADH, HEJ, SM, JW, PFW. Project administration: ALS. Resources: ALS. Software: ALS. Supervision: PFW. Validation: ALS, MMCE, LJS, HE, PMG, ADH, HEJ, SM, JW, PFW. Visualisation: ALS, MMCE, LJS, HE, PMG, ADH, HEJ, SM, JW, PFW. Writing—original draft: ALS. Writing—review and editing: ALS, MMCE, LJS, VC, HE, PMG, ADH, HEJ, SM, JW, PFW. All authors approved the final version of the manuscript.

Declaration of funding interests
This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment Programme (grant number NIHR129020). Athena L. Sheppard (Systematic Review Fellowship, grant number NIHR-RM-SR-2017-08-012) was funded by the NIHR for this research project. This research was supported by the NIHR Applied Research Collaboration West (NIHR ARC West) at University Hospital Bristol NHS Foundation Trust. The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care.

Declaration of personal interests
Athena L. Sheppard has received research funding from the National Institute for Health Research.
The authors wish to thank Alison Richards, Research Associate, and Sarah Dawson, Senior Research Associate in Information Retrieval, at NIHR ARC West at University Hospitals Bristol NHS Foundation Trust, and Population Health Sciences, Bristol Medical School, University of Bristol, UK, for performing the searches.