COMPARISON OF PROBABILITY OF STROKE BETWEEN THE COPENHAGEN-CITY-HEART-STUDY AND THE FRAMINGHAM-STUDY

Background and Purpose We wished to test the validity of a stroke prob ability point system from the Framingham Study for a sample of the pop ulation of Copenhagen, Denmark. In the Framingham cohort, the regressi on model of Cox established the effect on stroke of the following fact ors: age, systolic blood pressure, the use of antihypertensive therapy , diabetes mellitus, cigarette smoking, prior cardiovascular disease, atrial fibrillation, and left ventricular hypertrophy. Derived from th is model, stroke probabilities were computed for each sex based on a p oint system. The authors claimed that a physician can use this system for individual stroke prediction. Methods The Copenhagen City Heart St udy is a prospective survey of 19 698 women and men aged 20 years or o lder invited to two cardiovascular examinations at 5-year intervals. T he baseline examination included 3015 men and 3501 women aged 55 to 84 years; 474 stroke events occurred during 10 years of follow-up. In bo th cohorts initial cases of stroke and transient ischemic attack recor ded during 10 years of follow-up were used. We used the statistical mo del from the Framingham, Study to establish a corresponding stroke pro bability point system using data from the Copenhagen City Heart Study population. We then compared the effects of the relevant risk factors, their combinations, and the corresponding stroke probabilities. We al so assessed stroke events during 10 years of follow-up in several subg roups of the Copenhagen population with different combinations of risk factors. Results For the Copenhagen City Heart Study population some of the risk factors (diabetes mellitus, cigarette smoking, atrial fibr illation, and left ventricular hypertrophy) had regression coefficient s different from those of the Framingham Study population. Consequentl y, the probability of stroke for persons presenting these risk factors and their combinations varied between the two studies. For some other risk factors (age, blood pressure, and cardiovascular disease), no ma jor differences were found. The recorded frequency of stroke events in subgroups of the Copenhagen population was compatible with the estima ted probability intervals of stroke from the Copenhagen City Heart Stu dy and with those from the Framingham Study, but these intervals were very large. Conclusions The majority of risk factors for stroke identi fied by the Framingham Study also had a significant effect in the Cope nhagen City Heart Study population. The differences found could be due partly to different definitions of these factors used by the two stud ies. Although estimated stroke probabilities based on point systems fr om the Copenhagen City Heart Study and the Framingham Study were simil ar, the points scored in the two systems did not always correspond to the same combination of risk factors. Such systems can be used for est imating stroke probability in a given population, provided that the st atistical confidence limits are known and the definitions of risk fact ors are compatible. However, because of the large statistical uncertai nty, a prognostic index should not be applied for individual predictio n unless it is used as an indicator of high relative risk associated w ith the simultaneous presence of several risk factors.