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

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Abstract
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.