Coagulopathies in Ischemic Stroke
To the Editor:
In their progress review, Bushnell and Goldstein1 have meta-analyzed the current literature (mostly retrospective case-control studies) about coagulopathies in ischemic stroke. Based on their calculated pretest probabilities and recommendations of coagulation experts, they propose a testing strategy that might help to reduce and interpret coagulation tests in unselected patients with ischemic stroke.
However, in their carefully combined analysis, we miss an interpretation and estimation of the impact of coagulopathies in ischemic stroke, especially in the young. This can be achieved by calculating the attributable risk, which combines the pretest probability (reflecting the prevalence of the risk factor in the population) with the relative risk.2 Assuming the data given in the paper, the population-attributable risks for the reported coagulopathies can be calculated (Table 1⇓; assuming that the odds ratios are an estimate for the relative risk). These data indicate, especially for younger patients, that although the pretest probability is low, due to high odds ratios the attributable risk is high. For all patients, the estimated attributable risk of coagulopathies is only 2% to 8.7%, which is low compared with other risk factors such as hypertension (which had an attributable risk of 26% in the Rochester Project3 ).
As long as definitive guidelines and prospective population-based studies are lacking, coagulopathies have to be regarded as dominant ill-defining factors for many patients. We conclude that in younger patients, in whom common arteriosclerotic risk factors are often absent, it can be estimated that a considerable proportion of ischemic strokes are caused by genetic or acquired coagulopathies or other yet-to-be-defined coagulation defects.
- Copyright © 2001 by American Heart Association
Bushnell CD, Goldstein LB. Diagnostic testing for coagulopathies in patients with ischemic stroke. Stroke. 2000;31:3067–3078.
O’Fallon WM, Sicks JD. Attributable risk. In: Whisnant JP, ed. Stroke: Populations, Cohorts and Clinical Trials. Oxford, UK: Butterworth-Heinemann; 1993.
Whisnant JP. Modeling of risk factors for ischemic stroke: the Willis lecture. Stroke. 1997;28:1839–1843.
Drs Weih and Villringer estimated attributable risk for ACL, LA, APCR, and the prothrombin mutation in ischemic stroke. We would first like to clarify that our analysisR1 was based on a systematic literature review and not a meta-analysis.
Attributable risk estimates need to be calculated with multiple regression techniques so that each risk factor is adjusted for the others that may contribute to the outcome under consideration.R2 However, the majority of the odds ratios used by Drs Weih and Villringer to calculate these estimates were not adjusted for traditional stroke risk factors. This can lead to an overestimation of attributable risk. WhisnantR2 highlighted this problem during his 1997 Willis Lecture. He found that the unadjusted attributable risk for stroke for hypertension was 37% but decreased to 26% after adjustment for other risk factors and interactions in multiple regression modeling. In addition, O’Fallon and SicksR3 have shown that all stroke risk factors have a higher attributable risk in younger patients. This could lead to a further overestimation of the attributable risk associated with coagulopathies. Because of these concerns, we felt that we could not calculate the attributable risk associated with specific coagulopathies.
Our review focused on the prevalence of coagulopathies in ischemic stroke patients from case-control studies of highly selected patients. Population-based estimates of the prevalence of these coagulation disorders in the general population and in ischemic stroke patients, as well as the number of ischemic stroke patients without these coagulation disorders, are needed to provide the most valid assessment of population-attributable risk. Because of the low yield of specialized testing for coagulopathies, an assessment of traditional risk factors and etiologies is necessary before the diagnosis is pursued.
Bushnell CD, Goldstein LB. Diagnostic testing for coagulopathies in patients with ischemic stroke. Stroke. 2000;31:3067-3978.
Whisnant JP. Modeling of risk factors for ischemic stroke: the Willis Lecture. Stroke. 1997;28:1840-1844.
O’Fallon WM, Sicks JD. Attributable risk. In: Whisnant JP, ed. Stroke: Populations, Cohorts, and Clinical Trials. Oxford, UK: Butterworth-Heinemann; 1993.