Validation of ischemic cerebrovascular diagnoses in the health improvement network (THIN)

Purpose To evaluate the validity of recorded diagnoses of ischemic cerebrovascular events requiring hospitalization within The Health Improvement Network (THIN) UK primary care database. Methods We identified 15 397 individuals aged 40–84 years with a first recorded ischemic event in 2000–2004. Of these, 4239 had a code suggestive of a hospitalization within 2 weeks of the event. A three‐step strategy was used to validate the records of these patients: manual review of computerized medical records excluding free‐text comments; manual review including free‐text comments (which include information gained from specialists, hospital discharge letters and results of diagnostic tests) of a random sample of possible cases (n = 300) and non‐cases (n = 100); and review of full medical records of this random sample and a questionnaire completed by their primary care physician. The positive predictive value (PPV) of each step was calculated. The confirmation rate was used to estimate incidence in the general population. Results After step 1, 3447 individuals were classified as possible cases and 792 were excluded as non‐cases. After step 2, 82% of possible cases were still classified as such. Step 3 showed that inclusion of free‐text comments increased the PPV of a diagnosis from 76 to 86%. The weighted incidence of hospitalized ischemic cerebrovascular events was 1.73 per 1000 person‐years (95% CI:1.68–1.77). Conclusions THIN demonstrates a high validity for the study of ischemic cerebrovascular events when reviewing computer records with additional free‐text comments. Accuracy of hospitalization status was not as well recorded. Copyright © 2010 John Wiley & Sons, Ltd.