Serology-based diagnosis of coeliac disease in secondary care: a single-centre study in Norway

Background Coeliac disease (CeD) affects 1–2% of the western population. Diagnosis is based on serology and duodenal biopsy, but serology-based diagnosis in adults has been approved in Europe.Objective To evaluate the diagnostic performance of IgA anti-transglutaminase 2 (IgA-TG2) and IgG anti-deamidated gliadin peptides (IgG-DGP), and their combinations, compared with biopsy in a real-world secondary care setting.Methods Adult patients referred to secondary care endoscopy service at Oslo University Hospital for suspected CeD were invited to participate. CeD diagnosis followed European and Norwegian guidelines, requiring positive serology and mucosal damage.Results Among 312 evaluable patients, 215 were diagnosed with CeD between 2018 and 2024. Analysis of IgA-TG2 above threshold (>4 U/ml) showed 93% specificity and 94% sensitivity, while IgG-DGP (>20 U/ml) showed 88% specificity and 83% sensitivity. In ROC analyses, the AUC values were 0.98 and 0.95, respectively. Higher threshold (2x, 3x, 5x and 10x ULN) of IgA-TG2 increased specificity (99% to 100%) but lowered sensitivity (82% to 49%). Using IgG-DGP did not increase specificity but detected six missed CeD cases by IgA-TG2. Forty-two percent (n = 92) of cases could be diagnosed with a no-biopsy approach with 10x ULN IgA-TG2 at referral with 100% specificity.Conclusion Serology correlates strongly with histological changes, supporting diagnosis without gastroscopy. A 10x ULN threshold shows excellent specificity at the expense of sensitivity, thus lower thresholds may be preferable due to diminishing gains in specificity. IgG-DGP serves as a valuable complementary marker, that improves sensitivity and helps identify patients with weak IgA-TG2 responses.