Sarita Shrestha1, Ola Olén2,3,4, Carl Eriksson5, Asa Hallqvist Everhov2,3, Par Myrelid6 , Isabella Visuri5, The Swibreg Study Group, Jonas F Ludvigsson7, 8 Ida Schoultz1, Scott Montgomery4,9,10, Michael C Sachs2, Jonas Halfvarson5

Affiliates

1 School of Medical Sciences, Örebro University, Örebro 2 Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden 3 Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden 4 Department of pediatric gastroenterology and nutrition, Sachs' Children and Youth Hospital, Stockholm, Sweden 5 Department of Gastroenterology, Faculty of Medicine and Health, Örebro University, SE 70182 Örebro, Sweden 6 Division of surgery, Department of Clinical and Experimental Medicine, Faulty of Health Sciences, Linköping University and Department of Surgery, County Council of Östergötland Linköping, Sweden 7 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden 8 Department of Pediatrics, Örebro University Hospital, Örebro University, Örebro, Sweden 9 Clinical Epidemiology and Biostatistics, School of Medical Sciences, Örebro University, Örebro 10 Department of Epidemiology and Public Health, University College London, London, UK

Abstract

BACKGROUND: The Swedish National Patient Register (NPR) is an important data source for research and a previous study has shown a high validity for a diagnosis of inflammatory bowel disease (IBD) in cases registered both in the Swedish quality registry for IBD (SWIBREG) and the NPR. However, whether the information on International Classification of Diseases (ICD) codes from the NPR can be used to predict subgroups of IBD is unknown.

METHODS AND MATERIALS: Medical records of 1403 patients registered in SWIBREG were reviewed and classified according to international accepted criteria for subtype of IBD and according to the Montreal classification. The first two IBD-associated ICD codes in the NPR, 1966-2014, were used to predict incident diagnoses. NPR data during the 5 years prior the review of medical records were used for prediction of prevalent IBD. ICD diagnosis and procedure codes in the NPR were used to predict subgroups of patients according to the Montreal classification, as previously described. Positive predictive values (PPV) with 95% confidence interval were calculated.

RESULTS: Based on the medical records, 854 patients were diagnosed with CD, 519 patients with UC and 30 with IBD-U (Table 1a). Information on PPV for predicting incident and prevalent cases of IBD type and its various subgroups is shown in Table 2. Age at diagnosis were stratified to A1, A2 and A3 (A1≤16 years, A2:17-40 years, A3>40 years) for the ICD codes, and PPV were calculated to be 95% (95%CI=93–98), 96% (95%CI=95–97) and 90% (95%CI=86–94) respectively.

CONCLUSIONS: The validity was high for age at diagnosis, for types of IBD among incident and prevalent cases and some subtypes. However, the validity was less impressive in other subtypes and it should be considered in the future studies.