Summary

Risk factors for venous thrombo-embolism (VTE) in the blackpopulation are poorly characterized. Of 142 black cases testeda genetic cause was identified in only 9.1%: 4.2% had protein Cdeficiency, 2.8% protein S deficiency, 0.7% antithrombin deficiencyand 1.4% were heterozygous for FV Leiden. We hypothesisedthat elevated factor VIII levels constitute a candidaterisk factor for venous thrombosis in the black population.Factor VIII (FVIII:C) levels were determined in 100 blackpatients with VTE and 100 black controls in a casecontrolstudy. Of the patients 34% had a FVIII:C above 228 IU/dL (the90 th centile value in normal blacks) compared to 10% controls.Relative to those with FVIII:C below this value, odds ratio (OR)for risk of VTE was 4.64 (95% CI 2.02-10.85). When FVIII:Cbelow 150 IU/dL was used as a comparator, OR was 11.1 (95%CI 4.29-29.43). There was evidence for a dose-response rela-tionship.We propose that raised FVIII:C is a major risk factorfor VTE in black subjects with prevalence and odds ratioexceeding those reported for white subjects.