Astrid van Hylckama Vlieg

Activated protein C resistance determined with a thrombin generation-based test predicts for venous thrombosis in men and women

Summary. Activated protein C (APC) resistance, determined with a thrombin‐generation‐based APC resistance test, may explain risk differences of venous thrombosis in users of second‐ and third‐generation oral contraceptives (OC). To clinically validate this test, we analysed the Leiden thrombophilia case–control study (474 patients with a first episode of deep vein thrombosis and 474 age‐ and sex‐matched control subjects). Data for men and women were analysed separately. As hormonal status in women is known to strongly influence the APC sensitivity ratio (APCsr), additional strata (OC use and menopausal state) were defined. The APCsr was higher in all patients than in control subjects. Odds ratios (OR), using the 90th percentile of all control subjects (APCsr > 4·5) as cut‐off, were: 7·5 [95% confidence interval (CI) 1·6–33·8] for men, 3·0 (95% CI 1·0–8·8) for premenopausal women not using OC, 4·8 (95% CI 1·6–14·7) for premenopausal women using OC and 4·7 (95% CI 1·4–15·6) for postmenopausal women. After excluding the carriers of factor V Leiden, the OR became infinite for men (no control had an APCsr > 4·5), 1·4 (95% CI 0·2–8·2) for premenopausal women not using OC, 3·4 (95% CI 1·1–10·8) for premenopausal women using OC and 3·6 (95% CI 0·6–20·5) for postmenopausal women. A high APCsr, determined with the thrombin‐generation‐based APC resistance test, predicts venous thrombotic risk, in populations with and without factor V Leiden. In addition, acquired APC resistance resulting from OC use predicts an increased risk for venous thrombosis independent of factor V Leiden.

Does thrombophilia testing help in the clinical management of patients

Thrombophilia can be identified in about half of all patients presenting with venous thrombosis. Testing has increased tremendously for various indications, but whether the results of such tests help in the clinical management of patients has not been settled. Here, we review the most commonly tested thrombophilic abnormalities, i.e. protein C, protein S, and antithrombin deficiencies, the F5 R506Q (factor V Leiden) and F2 G20210A (prothrombin G20210A) mutations, and elevated levels of coagulation factor VIII, and their association with venous and arterial thrombosis as well as pregnancy complications. We conclude that testing for hereditary thrombophilia generally does not alter the clinical management of patients with venous or arterial thrombosis or pregnancy complications. Because testing for thrombophilia only serves limited purpose this should not be performed on a routine basis.

The Risk of Deep Venous Thrombosis Associated With Injectable Depot–Medroxyprogesterone Acetate Contraceptives or a Levonorgestrel Intrauterine Device

Objective—To assess the risk of venous thrombosis associated with nonoral contraceptives (ie, injectable depot–medroxyprogesterone acetate contraceptives, hormone [levonorgestrel]–releasing intrauterine devices, a contraceptive patch, or a contraceptive implant). Methods and Results—Analyses were performed in the Multiple Environmental and Genetic Assessment study, a large case-control study on risk factors for venous thrombosis. For the current analyses, we selected premenopausal women, aged 18 to 50 years, who were not pregnant nor within 4 weeks postpartum and were not using oral contraceptives; 446 patients and 1146 controls were included. Injectable depot–medroxyprogesterone acetate contraceptives were associated with a 3.6-fold (95% CI, 1.8- to 7.1-fold) increased risk of venous thrombosis compared with nonusers of hormonal contraceptives. The use of a levonorgestrel intrauterine device was not associated with an increased risk (odds ratio, 0.3; 95% CI, 0.1 to 1.1). Unfortunately, the few women using a contraceptive patch or an implant prevented a reliable estimate of the risk of thrombosis. Conclusion—The risk of venous thrombosis was increased for injectable depot–medroxyprogesterone acetate contraceptive users, while we were able to reliably exclude an increased risk associated with levonorgestrel intrauterine device use. Therefore, the latter seems to be the safest option regarding the risk of venous thrombosis.

Factor XIII Val34Leu polymorphism, factor XIII antigen levels and activity and the risk of deep venous thrombosis.

Summary. Varying results on the effect of factor XIII (FXIII) Val34Leu on venous thrombotic risk have been reported. The probability of a true association between this polymorphism and venous thrombotic risk would be enhanced by a laboratory phenotype associated with this polymorphism and with the thrombotic risk. The aim of this study was to assess the effect of FXIII Val34Leu, FXIII activity and subunit levels on venous thrombotic risk in a large case–control study, The Leiden Thrombophilia study (LETS). We found higher FXIII activity for 34Leu carriers (Leu/Leu: 158·0, Val/Val: 95·0). FXIII subunit levels were not associated with genotype. Higher FXIII activity was associated with a slightly decreased thrombotic risk [Odds ratio (OR): 0·8, 95% confidence intervals (CI): 0·5–1·3]. This effect was not present for elevated FXIII subunit levels. Higher FXIII activity was also associated with a higher dissociation index (percentage A2B2 complex dissociated after activation by thrombin for a fixed time interval). This index was higher for FXIII 34Leu carriers. The risk of deep venous thrombosis was slightly decreased for carriers of the 34Leu allele [OR: 0·9 (95%CI: 0·7–1·1)]. For homozygous 34Leu carriers the OR was 0·7 (95%CI: 0·4–1·3). This finding, suggesting a weak protective effect, was completely restricted to men. An overall estimate of thrombotic risk was calculated by using earlier reports on the risk of FXIII Val34Leu. The overall risk estimate for homozygous 34Leu carriers was 0·8 (95%CI: 0·6–1·0). In this study, a weak protective effect against venous thrombosis was found, of FXIII 34Leu as well as of increased FXIII activity.

Genetic variation associated with plasma vonWillebrand factor levels and the risk of incident venous thrombosis

In a recent genome-wide association study, variants in 8 genes were associated with VWF level, a risk factor for venous thrombosis (VT). In an independent, population-based, case-control study of incident VT, we tested hypotheses that variants in these genes would be associated with risk. Cases were 656 women who experienced an incident VT, and controls comprised 710 women without a history of VT. DNA was obtained from whole blood. Logistic regression was used to test associations between incident VT and single nucleotide polymorphisms (SNPs) in 7 genes not previously shown to be associated with VT. Associations with P < .05 were candidates for replication in an independent case-control study of VT in both sexes. Two of the 7 SNPs tested yielded P < .05: rs1039084 (P = .005) in STXBP5, a novel candidate gene for VT, and rs1063856 (P = .04) in VWF, a gene whose protein level is associated with VT risk. Association results for the remaining 5 variants in SCARA5, STAB2, STX2, TC2N, and CLEC4M were not significant. Both STXBP5 and VWF findings were replicated successfully. Variation in genes associated with VWF levels in the genome-wide association study was found to be independently associated with incident VT.

Broadening the factor V Leiden paradox: pulmonary embolism and deep-vein thrombosis as 2 sides of the spectrum.

Risk factors for deep-vein thrombosis have been shown not to be always the same as for pulmonary embolism. A well-known example is the factor V Leiden (FVL) paradox: the FVL mutation poses a clearly higher risk for deep-vein thrombosis (DVT) than for pulmonary embolism. We aimed to expand this paradox and therefore present risk estimates for several established risk factors for DVT and pulmonary embolism separately. When such separate risk estimates could not be retrieved from the literature, we calculated these risks in our own data, a large population-based case-control study on venous thrombosis (the MEGA study). Our results showed that the FVL paradox can be broadened (ie, the risk factors oral contraceptive use, pregnancy, puerperium, minor leg injuries, and obesity have an effect comparable with FVL). Furthermore, we found that pulmonary conditions, such as chronic obstructive pulmonary disease, pneumonia, and sickle cell disease, were risk factors with an opposite effect: a higher risk of pulmonary embolism, but little or no effect on DVT. These findings suggest that pulmonary embolism and DVT may not always have the same etiology, and encourage unraveling this phenomenon in further studies.

Long-Term Survival in a Large Cohort of Patients with Venous Thrombosis: Incidence and Predictors

Linda Flinterman and colleagues report on the long-term mortality rate for individuals who have experienced a first venous thrombosis or pulmonary embolism. They describe an ongoing elevated risk of death for individuals who had experienced a venous thrombosis or pulmonary embolism as compared to controls, for up to eight years after the event.

Protein Z and protein Z-dependent protease inhibitor - Determinants of levels and risk of venous thrombosis

To assess the potential roles of protein Z (PZ) and protein Z-dependent protease inhibitor (ZPI) in venous thrombosis, their plasma levels were measured in 426 individuals with venous thrombosis and 471 control individuals participating in the Leiden Thrombophilia Study. A relationship between the level of PZ or ZPI and venous thrombosis was not detected in the overall case-control study. PZ and ZPI circulate as a complex and their plasma levels are interdependent. Both PZ and ZPI are increased with oral contraceptive use and reduced with oral anticoagulant therapy.

Lower Risk of Cardiovascular Events in Postmenopausal Women Taking Oral Estradiol Compared With Oral Conjugated Equine Estrogens

IMPORTANCE Little is known about the comparative cardiovascular safety of oral hormone therapy products, which impedes women from making informed safety decisions about hormone therapy to treat menopausal symptoms. OBJECTIVE To compare the relative clinical cardiovascular safety of 2 commonly used oral estrogen drugs-conjugated equine estrogens (CEEs) and estradiol. DESIGN, SETTING, AND PARTICIPANTS Population-based, case-control study from January 1, 2003, to December 31, 2009, comparing cardiovascular event risk associated with current CEEs and estradiol use in a large health maintenance organization in which the preferred formulary estrogen changed from CEEs to estradiol during the course of data collection. Participants were 384 postmenopausal women aged 30 to 79 years using oral hormone therapy. MAIN OUTCOMES AND MEASURES Incident venous thrombosis was the primary clinical outcome, and incident myocardial infarction and ischemic stroke were secondary outcomes. As validation, an intermediate clotting phenotype, the endogenous thrombin potential-based normalized activated protein C sensitivity ratio, was measured in plasma of controls. RESULTS We studied 68 venous thrombosis, 67 myocardial infarction, and 48 ischemic stroke cases, with 201 matched controls; all participants were current users of oral CEEs or estradiol. In adjusted analyses, current oral CEEs use compared with current oral estradiol use was associated with an increased venous thrombosis risk (odds ratio, 2.08; 95% CI, 1.02-4.27; P = .045) and an increased myocardial infarction risk that did not reach statistical significance (odds ratio, 1.87; 95% CI, 0.91-3.84; P = .09) and was not associated with ischemic stroke risk (odds ratio, 1.13; 95% CI, 0.55-2.31; P = .74). Among 140 controls, CEEs users compared with estradiol users had higher endogenous thrombin potential-based normalized activated protein C sensitivity ratios (P < .001), indicating a stronger clotting propensity. CONCLUSIONS AND RELEVANCE In an observational study of oral hormone therapy users, CEEs use was associated with a higher risk of incident venous thrombosis and possibly myocardial infarction than estradiol use. This risk differential was supported by biologic data. These findings need replication and suggest that various oral estrogen drugs may be associated with different levels of cardiovascular risk.

Genetic Variations Associated with Recurrent Venous Thrombosis

Background—The prediction of recurrent venous thrombosis using individual genetic risk predictors has proven to be challenging. The aim of this study was to assess whether multiple genetic single nucleotide polymorphism (SNP) analysis would predict recurrent venous thrombosis. Methods and Results—Patients with a first venous thrombosis were followed for a recurrent venous thrombosis up to 2009 (MEGA follow-up study), which occurred in 608 out of 4100 patients (2.7%/year). Thirty-one common thrombosis-associated single nucleotide polymorphisms (SNPs) were associated with the risk of recurrence. A genetic risk score (GRS) for each individual was calculated by summing the number of risk-increasing alleles for each of the 31 SNPs and for a simplified model consisting of 5 SNPs: rs6025, rs1799963, rs8176719, rs2066865, and rs2036914. The risk of recurrence associated with the GRS was calculated continuously and after stratification in a low and high score. All individual SNPs were at most mildly associated with recurrence risk. Regarding the 31-SNP GRS, recurrence risk was highest in patients with ≥31 and lowest in patients with <21 risk alleles. The discriminative power of the 5-SNP GRS was similar to that of the 31-SNP GRS. The 6-year cumulative incidence of recurrence was high for individuals with ≥5 (20.3%; 95% confidence interval, 16.5–24.1) and low for individuals with ⩽1 (9.4%; 95% confidence interval, 6.7–12.1) risk alleles. Predictive power improved after stratification into provoked and unprovoked first events and sex. Conclusions—Multiple genetic SNP analysis is useful in the prediction of recurrent thrombosis, even more so when combining this model with clinical risk factors.