ALBERT

Description: Hyperhomocysteinemia is demonstrated as a risk factor for venous and arterial thrombosis. Experimental evidence suggests that its thrombogenic propensity results from endothelial dysfunction and injury followed by platelet and fibrin formation. However, lowering homocysteine concentrations with vitamin B6, B12 or folic acid has not resulted in a reduced risk of recurrent venous and arterial thrombosis in large prospective clinical trials. This suggests that hyperhomocysteinemia is a surrogate for another thrombophilic related specimen. As high factor VIII:C levels are associated with an increased risk of both venous and arterial thrombosis, and with endothelial injury, we hypothesize that hyperhomocysteinemia and factor VIII:C levels are closely related to each other. Therefore, we performed a study to assess the absolute risk of thrombosis in hyperhomocysteinemia and the effects of elevated factor VIII:C levels on this risk in a large cohort of families with hereditary (index) deficiencies of protein S, protein C or antithrombin. Hyperhomocysteinemia was defined as a fasting plasma homocysteine level above 18.5 μmol/l and factor VIII:C levels were elevated when higher than 150%. A total of 405 relatives were included. Median factor VIII:C levels in hyperhomocysteinemic relatives (n=26, 6%) were 169%, compared to 136% in normohomocysteinemic relatives (P=0.004) (Figure) and were more often elevated (65 vs. 38%, P=0.006). Other thrombophilic defects, including the index deficiencies, factor V Leiden and the prothrombin mutation were equally divided. Hyperhomocysteinemia was associated with an increased risk of venous and arterial thrombosis (relative risk’s 2.6 [1.3–4.8] and 3.7 [1.5–8.4)], respectively). Relatives with elevated factor VIII:C levels were also at risk; relative risk 2.3 (1.4–4.0) for venous thrombosis and 2.3 (1.0–5.1) for arterial thrombosis. After excluding all relatives with elevated factor VIII:C levels, relative risk for venous thrombosis and hyperhomocysteinemia dropped to 1.3 (0.2–9.8) and nil relatives had arterial thrombosis. These results suggest that hyperhomocysteinemia indeed is an epiphenomenon for elevated factor VIII:C levels and therefore homocysteine measurements can be omitted in risk assessment for venous and arterial thrombosis when factor VIII:C measurements are incorporated in thrombophilia screening. Figure Figure

Description: Hyperhomocysteinemia is a risk factor for venous and arterial thrombosis. Different diagnostic strategies are used to identify subjects at risk of thrombosis, related to hyperhomocysteinemia. Measurements of fasting and methionine-loading levels are usually recommended. Alternatively, random homocysteine measurements may simplify the procedure. Random levels 〈 10 and 〉 20 μmol/l are considered to indicate normohomocysteinemia and hyperhomocysteinemia, respectively, while consecutive fasting and methionine-loading tests are required at levels 10–20 μmol/l. We performed a study to assess the most suitable strategy in a large cohort of families with hereditary (index) deficiencies of protein S, protein C or antithrombin. Random, fasting and methionine-loading homocysteine samples were measured in 713 relatives. According to predefined cut-off levels hyperhomocysteinemic and normohomocysteinemic relatives were identified and their absolute risks of thrombosis were compared. Relatives with random homocysteine levels 〉 20 μmol/l were not at risk of venous or arterial thrombosis compared to relatives with levels 〈 10 μmol/l (relative risks 0.9 [95% CI, 0.4–2.3] and 1.7 [0.5–5.7], respectively). Fasting hyperhomocysteinemia (homocysteine levels 〉 18.5 μmol/l) was associated with an increased risk of venous and arterial thrombosis (relative risks 2.6 [1.3–4.8] and 3.7 [1.5–8.4)], respectively) (Table). Relatives with normal fasting homocysteine levels, but methionine-loading hyperhomocysteinemia (homocysteine levels 〉 58.8 μmol/l) were not at risk; relative risk 0.8 (0.2–1.9) for venous thrombosis and 1.1 (0.2–3.9) for arterial thrombosis. Exclusion of relatives with an index deficiency did not alter the risk estimates, while annual incidences of normohomocysteinemic relatives decreased to 0.19% per year (0.12–0.29), which is comparable with the annual incidence in the normal population. As only fasting homocysteine identified subjects at risk of thrombosis, random homocysteine and methionine-loading tests can be omitted in clinical practice. Venous Thrombosis Observation Relatives Incidence/year (%) Relative Risk years with event (95% CI) (95% CI) * Methionine-loading performed in relatives with no fasting hyperhomocysteinemia Fasting Homocysteine No hyperhomocysteinemia 10408 55 0.53 (0.40–0.69) Reference Hyperhomocysteinemia 804 11 1.37 (0.68–2.45) 2.6(1.3–4.8) Methionine-loading test* No hyperhomocysteinemia 9341 50 0.54 (0.40–0.71) Reference Hyperhomocysteinemia 986 4 0.41 (0.11–1.04) 0.8(0.2–1.9) Arterial Thrombosis Fasting Homocysteine No hyperhomocysteinemia 11096 21 0.19 (0.12–0.29) Reference Hyperhomocysteinemia 1004 7 0.70 (0.28–1.44) 3.7(1.5–8.4) Methionine-loading test* No hyperhomocysteinemia10008 10008 19 0.19 (0.11–0.30) Reference Hyperhomocysteinemia 1000 2 0.20 (0.02–0.72) 1.1(0.2–3.9)

Description: Key Points Immediate compression therapy after DVT is associated with a 20% absolute reduction of RVO. The reduction of residual thrombosis is associated with an 8% absolute reduction of postthrombotic syndrome at 24 months.

Description: The prothrombin 20210A mutation has been associated with an increased risk for venous thromboembolism (VTE) and arterial cardiovascular disease. The risks for asymptomatic carriers of this mutation have thus far been studied only in case-control and retrospective cohort studies. Here we present the results of the first prospective observational study in asymptomatic first-degree family members of patients with either VTE or premature atherosclerosis and the prothrombin 20210A mutation. We included 464 individuals (236 carriers) with a total follow-up duration of 1816 years (943 years for the carriers). The annual incidence of a first VTE was 0.37% (95% CI, 0.08-1.08) for carriers and 0.12% (95% CI, 0.00-0.69) for noncarriers (HR, 3.1; 95% CI, 0.3-29.6). The annual incidence of a first arterial cardiovascular event was 0.56% (95% CI, 0.18-1.31) for carriers and 0.73% (95% CI, 0.27-1.58) for noncarriers (adjusted HR, 0.7; 95% CI, 0.2-2.5). We conclude that the absolute incidence of a first VTE or arterial cardiovascular event is low; therefore, the clinical implications of carriership of the prothrombin 20210A mutation are limited, and routinely testing all first-degree relatives of probands with this mutation does not appear to be justified.