Comparison of different procedures to identify probable cases of myocardial infarction and stroke in two Swedish prospective cohort studies using local and national routine registers

In prospective cohort studies, person-time time is calculated from baseline until the first definite event occurs or until censoring. A way to correct ly identify and date definite events when only routine registers are availa ble is to retrieve all hospital discharge notes and death certificates with a diagnosis of probable event and perform a consecutive revision. It is im portant to detect all possible hospital stays as they may contain useful in formation for the revision study. Furthermore, loss to follow-up can be avo ided by extending the retrieval outside the specific geographical area wher e the cohort was defined. The aims of this study were (i) to describe a com prehensive retrieval of probable myocardial infarctions (diagnosis with Int ernational Classification of Diseases 8th and 9th revisions codes 410-414) or stroke (codes 430-438), (ii) to quantify the relative efficiency of diff erent local and national routine registers or their combination compared wi th the use of all available registers together, and (iii) to audit local an d national registers by comparing their outcome at the county level. The st udy was performed in two prospective cohorts studies i.e., 'Men-born-1914' (n = 500) from Skane (period 1982-1993), and Skara-1 (n = 683) from Skarabo rg (period 1988-1994.). All available routine registers were linked to the cohorts. The use of all available routine registers improved retrieval of b oth individual and hospital stays with a discharge diagnosis of probable ev ent and gave an enhanced basis for a future validation study. Local registe rs were not completely covered by the national register, but the accessible combination of national in-patient and mortality registers was an efficien t alternative.