Identification of Patients with Colon Ischemia in the Swedish ESPRESSO Cohort: A Validation Study

Colon ischemia is the most common form of intestinal ischemia, yet case identification in epidemiological research remains challenging due to heterogeneous diagnostic criteria and absence of a specific International Classification of Diseases (ICD) code. The use of SNOMED (Systematized Nomenclature of Medicine) for gastrointestinal biopsies and surgical specimens enables a unique possibility to identify colon ischemia cases.

In this validation study, 231 individuals with SNOMED code M54 (necrosis) and colorectal topography codes (T67-T68) were randomly selected from five Swedish regions. Medical charts were retrieved for 204 cases, where 143 contained sufficient information for evaluation. Cases were classified by clinical overall assessment and assigned an etiological group. Positive predictive values (PPVs) were calculated for overall colon ischemia based on histopathology alone and for etiological subsets where histopathology was combined with ICD codes.

Of 143 patients with sufficient clinical information for validation, histopathological ischemic injury of the colon was confirmed in 141, corresponding to a PPV of 99% (95% CI, 95-99%). Combining SNOMED codes with selected ICD codes yielded a PPV of 84% (95% CI, 73-92%) for clinically confirmed idiopathic colon ischemia, increasing to 92% (95% CI, 79-98%) when more restrictive ICD-based criteria were applied.

SNOMED-based histopathological case identification demonstrated a very high PPV for ischemic injury of the colon but could not distinguish idiopathic disease from ischemia secondary to identifiable clinical conditions. Combining SNOMED and ICD codes provides a feasible and reproducible strategy for identifying underlying causes of colon ischemia in Swedish nationwide health registers.