Genomic and transcriptomic association studies identify 16 novel susceptibility loci for venous thromboembolism.

Venous thromboembolism (VTE) is a significant contributor to morbidity and mortality. To advance our understanding of the biology contributing to VTE, we conducted a genome-wide association study (GWAS) of VTE and a transcriptome-wide association study (TWAS) based on imputed gene expression from whole blood and liver. We meta-analyzed GWAS data from 18 studies for 30 234 VTE cases and 172 122 controls and assessed the association between 12 923 718 genetic variants and VTE. We generated variant prediction scores of gene expression from whole blood and liver tissue and assessed them for association with VTE. Mendelian randomization analyses were conducted for traits genetically associated with novel VTE loci. We identified 34 independent genetic signals for VTE risk from GWAS meta-analysis, of which 14 are newly reported associations. This included 11 newly associated genetic loci (C1orf198, PLEK, OSMR-AS1, NUGGC/SCARA5, GRK5, MPHOSPH9, ARID4A, PLCG2, SMG6, EIF5A, and STX10) of which 6 replicated, and 3 new independent signals in 3 known genes. Further, TWAS identified 5 additional genetic loci with imputed gene expression levels differing between cases and controls in whole blood (SH2B3, SPSB1, RP11-747H7.3, RP4-737E23.2) and in liver (ERAP1). At some GWAS loci, we found suggestive evidence that the VTE association signal for novel and previously known regions colocalized with expression quantitative trait locus signals. Mendelian randomization analyses suggested that blood traits may contribute to the underlying risk of VTE. To conclude, we identified 16 novel susceptibility loci for VTE; for some loci, the association signals are likely mediated through gene expression of nearby genes.

Venous Thromboembolism (VTE) Incidence and VTE-Associated Survival among Olmsted County Residents of Local Nursing Homes.

Nursing home (NH) residency is an independent risk factor for venous thromboembolism (VTE), but the VTE burden within the NH population is uncertain. This study estimates VTE incidence and VTE-associated mortality among NH residents. We identified all NH residents in any NH in Olmsted County, Minnesota, United States, 1 October 1998 to 31 December 2005 and all first lifetime VTE among county residents to estimate VTE incidence while resident of local NHs (NHVTE), using Centers for Medicare and Medicaid Services Minimum Data Set and Rochester Epidemiology Project resources. We tested associations between NHVTE and age, sex and time since each NH admission using Poisson modelling. Additionally, we tested incident NHVTE as a potential predictor of survival using Cox proportional hazards, adjusting for age, sex and NH residency. Between 1 October 1998 and 31 December 2005, 3,465 Olmsted County residents with ≥1 admission to a local NH, contributed 4,762 NH stays. Of the 3,465 NH residents, 111 experienced incident NHVTE (2.3% of all eligible stays), for an overall rate of 3,653/100,000 NH person-years (NH-PY). VTE incidence was inversely associated with time since each NH admission, and was highest in the first 7 days after each NH admission (18,764/100,000 NH-PY). The adjusted hazard of death for incident NHVTE was 1.90 (95% confidence interval [CI]: 1.38-2.62). In conclusion, VTE incidence among NH residents was nearly 30-fold higher than published incidence rates for the general Olmsted County population. VTE incidence was highest within 7 days after NH admission, and NHVTE was associated with significantly reduced survival. These data can inform future research and construction of clinical trials regarding short-term prophylaxis.

Diagnostic laboratory standardization and validation of platelet transmission electron microscopy.

Platelet transmission electron microscopy (PTEM) is considered the gold standard test for assessing distinct ultrastructural abnormalities in inherited platelet disorders (IPDs). Nevertheless, PTEM remains mainly a research tool due to the lack of standardized procedures, a validated dense granule (DG) count reference range, and standardized image interpretation criteria. The aim of this study was to standardize and validate PTEM as a clinical laboratory test. Based on previously established methods, we optimized and standardized preanalytical, analytical, and postanalytical procedures for both whole mount (WM) and thin section (TS) PTEM. Mean number of DG/platelet (plt), percentage of plts without DG, platelet count (PC), mean platelet volume (MPV), immature platelet fraction (IPF), and plt light transmission aggregometry analyses were measured on blood samples from 113 healthy donors. Quantile regression was used to estimate the reference range for DG/plt, and linear regression was used to assess the association of DG/plt with other plt measurements. All PTEM procedures were standardized using commercially available materials and reagents. DG interpretation criteria were established based on previous publications and expert consensus, and resulted in improved operator agreement. Mean DG/plt was stable for 2 days after blood sample collection. The median within patient coefficient of variation for mean DG/plt was 22.2%; the mean DG/plt reference range (mid-95th %) was 1.2-4.0. Mean DG/plt was associated with IPF (p = .01, R2 = 0.06) but not age, sex, PC, MPV, or plt maximum aggregation or primary slope of aggregation (p > .17, R2 < 0.02). Baseline ultrastructural features were established for TS-PTEM. PTEM was validated using samples from patients with previously established diagnoses of IPDs. Standardization and validation of PTEM procedures and interpretation, and establishment of the normal mean DG/plt reference range and PTEM baseline ultrastructural features, will facilitate implementation of PTEM as a valid clinical laboratory test for evaluating ultrastructural abnormalities in IPDs.

Correction to: Assessing the causal relationship between obesity and venous thromboembolism through a Mendelian Randomization study.

The co-author name Immaculata DeVivo was incorrectly published. The correct name is given below.

Coronary Embolus: An Underappreciated Cause of Acute Coronary Syndromes.

Coronary embolism is the underlying cause of 3% of acute coronary syndromes but is often not considered in the differential of acute coronary syndromes. It should be suspected in the case of high thrombus burden despite a relatively normal underlying vessel or recurrent coronary thrombus. Coronary embolism may be direct (from the aortic valve or left atrial appendage), paroxysmal (from the venous circulation through a patent foramen ovale), or iatrogenic (following cardiac intervention). Investigations include transesophageal echocardiography to assess the left atrial appendage and atrial septum and continuous electrocardiographic monitoring to assess for paroxysmal atrial fibrillation. The authors review the historic and contemporary published data about this important cause of acute coronary syndromes. The authors propose an investigation and management strategy for work-up and anticoagulation strategy for patients with suspected coronary embolism.

Is Infection an Independent Risk Factor for Venous Thromboembolism? A Population-Based, Case-Control Study.

BACKGROUND: The independent association of recent infection with venous thromboembolism is uncertain. The study aims were to test both overall infection (site unspecified) and specific infection sites as potential risk factors for deep vein thrombosis and pulmonary embolism adjusting for other known venous thromboembolism factors. METHODS: By using Rochester Epidemiology Project resources, we identified all Olmsted County, Minnesota, residents with objectively diagnosed incident deep vein thrombosis or pulmonary embolism over the 13-year period 1988 to 2000 (cases; n = 1303) and 1 to 2 residents without venous thromboembolism matched to each case on age, sex, and incident venous thromboembolism date (controls; n = 1494). Using conditional logistic regression, we tested recent infection and infection site(s) for an association with venous thromboembolism, adjusting for body mass index, smoking, current/recent hospitalization with/without surgery, nursing home confinement, active cancer, trauma/fracture, leg paresis, prior superficial vein thrombosis, transvenous catheter/pacemaker, ischemic heart disease, congestive heart failure, chronic lung or renal disease, serious liver disease, asthma, diabetes mellitus, hormone therapy, and pregnancy/postpartum. RESULTS: A total of 513 cases (39.4%) and 189 controls (12.7%) had an infection in the previous 92 days (odds ratio, 4.5; 95% confidence interval, 3.6-5.5; P < .0001). In a multivariable analysis adjusting for common venous thromboembolism risk factors, pneumonia and symptomatic urinary tract, oral, intra-abdominal, and systemic bloodstream infections were associated with significantly increased odds of venous thromboembolism. CONCLUSIONS: Infection as a whole and specific infection sites in particular are independent risk factors for venous thromboembolism and should be considered as potential indications for venous thromboembolism prophylaxis.

Identification of Genetic Interaction with Risk Factors Using a Time-To-Event Model.

BACKGROUND: Certain diseases can occur with and without a trigger. We use Venous Thromboembolism (VTE) as our example to identify genetic interaction with pregnancy in women with VTE during pre- or postpartum. Pregnancy is one of the major risk factors for VTE as it accounts for 10% of maternal deaths. METHODS: We performed a whole genome association analysis using the Cox Proportional Hazard (CoxPH) model adjusted for covariates to identify genetic variants associated with the time-to-event of VTE related to pre- or postpartum during the childbearing age of 18-45 years using a case-only design in a cohort of women with VTE. Women with a VTE event after 45 years of age were censored and contributed only follow-up time. RESULTS: We identified two intragenic single nucleotide polymorphisms (SNPs) at genome-wide significance in the PURB gene located on chromosome 7, and two additional intragenic SNPs, one in the LINGO2 gene on chromosome 9 and one in RDXP2 on chromosome X. CONCLUSIONS: We showed that the time-to-event model is a useful approach for identifying potential hazard-modification of the genetic variants when the event of interest (VTE) occurs due to a risk factor (pre- or post-partum).

The Impact of Antithrombin Deficiency on Women's Reproductive Health Experiences and Healthcare Decision-Making.

BACKGROUND: Women with inherited antithrombin (AT) deficiency are at high risk for venous thromboembolism (VTE), especially during times of estrogen exposure, but little is known about patient-oriented reproductive decision-making in this population. MATERIALS AND METHODS: Provider-administered survey of women with AT deficiency. Participants were asked to discuss their diagnosis of AT deficiency and questioned about (1) contraception, (2) pregnancies, and (3) menorrhagia, and the impact of their AT deficiency on each reproductive health experience. RESULTS: Of 31 women with inherited AT deficiency, 18 (58%) were surveyed, 8 (26%) were unreachable, and 5 (16%) were deceased. Twelve (67%) had a VTE, including two which occurred during pregnancy and five during oral contraceptive (OCP) use. Women reported using OCPs, intrauterine device (IUD), and condoms for contraception. Of five women diagnosed with AT deficiency while taking OCPs, three switched to an IUD, one to condoms, and one used no alternative method. Eighteen women reported 42 total pregnancies, with 33 (79%) resulting in live term birth, 3 (7%) in live preterm birth, and 6 (14%) in spontaneous abortion at a median of 12 weeks. Four (22%) women reported the use of anticoagulation during pregnancy. Eleven (61%) women reported menorrhagia and 4 (36%), while on anticoagulation for VTE events. Ten of 18 women (56%) reported that the diagnosis of AT had affected their reproductive health in some way. CONCLUSION: Women with AT deficiency require careful multidisciplinary management to avoid complications in the setting of contraception and pregnancy. AT deficiency impacts women's reproductive health experiences and patient-oriented reproductive decision-making is key.

Assessing the causal relationship between obesity and venous thromboembolism through a Mendelian Randomization study.

Observational studies have shown an association between obesity and venous thromboembolism (VTE) but it is not known if observed associations are causal, due to reverse causation or confounding bias. We conducted a Mendelian Randomization study of body mass index (BMI) and VTE. We identified 95 single nucleotide polymorphisms (SNPs) that have been previously associated with BMI and assessed the association between genetically predicted high BMI and VTE leveraging data from a previously conducted GWAS within the INVENT consortium comprising a total of 7507 VTE cases and 52,632 controls of European ancestry. Five BMI SNPs were associated with VTE at P < 0.05, with the strongest association seen for the FTO SNP rs1558902 (OR 1.07, 95% CI 1.02-1.12, P = 0.005). In addition, we observed a significant association between genetically predicted BMI and VTE (OR = 1.59, 95% CI 1.30-1.93 per standard deviation increase in BMI, P = 5.8 × 10-6). Our study provides evidence for a causal relationship between high BMI and risk of VTE. Reducing obesity levels will likely result in lower incidence in VTE.

Effect of a near-universal hospitalization-based prophylaxis regimen on annual number of venous thromboembolism events in the US.

The annual number of US venous thromboembolism (VTE) events, the number of potentially preventable events, and the effect of hospitalization-based prophylaxis are uncertain. We estimated VTE attack (incident plus recurrent VTE) rates and the total annual number of US VTE events related and unrelated to hospitalization using Rochester Epidemiology Project resources to identify all Olmsted County, Minnesota, residents with incident or recurrent VTE over the 6-year period 2005-2010. The average annual VTE attack rates related and unrelated to hospitalization were 282 and 8 per 10 000 person-years, respectively. The estimated average number of US VTE events was 495 669 per year (48% unrelated to hospitalization). Among Olmsted County residents hospitalized at a Mayo Clinic hospital from 2005 to 2010, the proportion of patients receiving VTE prophylaxis or with an indication that prophylaxis was unnecessary increased from ∼40% in 2005 to ∼90% by 2010. The annual age- and sex-adjusted hospitalization-related (in-hospital) VTE attack rates from 2005 to 2010 ranged from 251 to 306 (1155 to 1751) per 10 000 person-years (bed-years) and did not change significantly. The median durations of hospitalization and in-hospital prophylaxis were 3 days and 70 hours, respectively. A total of 75% of VTE events occurred after hospital discharge, with a 19.5-day median time to VTE. Additional efforts are needed to identify the individual inpatient and outpatient at high risk for incident and recurrent VTE and target (longer duration) primary and secondary prophylaxis to high-risk individuals who would benefit most.

Thrombin generation profiles as predictors of symptomatic venous thromboembolism after trauma: A prospective cohort study.

BACKGROUND: Reliable biomarkers predictive of venous thromboembolism (VTE) after acute trauma are uncertain. The objective of the study was to identify risk factors for symptomatic VTE after trauma, including individual plasma coagulome characteristics as reflected by thrombin generation. METHODS: In a prospective, case-cohort study, trauma patients were enrolled over the 4.5-year period, 2011 to 2015. Blood was collected by venipuncture into 3.2% trisodium citrate at 0, 6, 12, 24, and 72 hours after injury and at hospital discharge. Platelet poor plasma was stored at -80 °C until analysis. Thrombin generation, as determined by the calibrated automated thrombogram (CAT) using 5 pM tissue factor (TF)/4 µM phospholipid (PS), was reported as peak height (nM thrombin) and time to peak height (ttPeak [minutes]). Data are presented as median [IQR] or hazard ratio with 95% CI. RESULTS: Among 453 trauma patients (injury severity score = 13.0 [6.0, 22.0], hospital length of stay = 4.0 [2.0, 10.0] days, age = 49 [28, 64] years, 71% male, 96% with blunt mechanism, mortality 3.2%), 83 developed symptomatic VTE within 92 days after injury (35 [42%] after hospital discharge). In a weighted, multivariate Cox model that included clinical and CAT characteristics available within 24 hours of admission, increased patient age (1.35 [1.19,1.52] per 10 years, p < 0.0001), body mass index ≥30 kg/m (4.45 [2.13,9.31], p < 0.0001), any surgery requiring general anesthesia (2.53 [1.53,4.19], p = 0.0003) and first available ttPeak (1.67 [1.29, 2.15], p < 0.00001) were independent predictors of incident symptomatic VTE within 92 days after trauma (C-statistic = 0.799). CONCLUSION: The individual's plasma coagulome (as reflected by thrombin generation) is an independent predictor of VTE after trauma. Clinical characteristics and ttPeak can be used to stratify acute trauma patients into high and low risk for VTE. LEVEL OF EVIDENCE: Prognostic, level III.

Identification of unique venous thromboembolism-susceptibility variants in African-Americans.

To identify novel single nucleotide polymorphisms (SNPs) associated with venous thromboembolism (VTE) in African-Americans (AAs), we performed a genome-wide association study (GWAS) of VTE in AAs using the Electronic Medical Records and Genomics (eMERGE) Network, comprised of seven sites each with DNA biobanks (total ~39,200 unique DNA samples) with genome-wide SNP data (imputed to 1000 Genomes Project cosmopolitan reference panel) and linked to electronic health records (EHRs). Using a validated EHR-driven phenotype extraction algorithm, we identified VTE cases and controls and tested for an association between each SNP and VTE using unconditional logistic regression, adjusted for age, sex, stroke, site-platform combination and sickle cell risk genotype. Among 393 AA VTE cases and 4,941 AA controls, three intragenic SNPs reached genome-wide significance: LEMD3 rs138916004 (OR=3.2; p=1.3E-08), LY86 rs3804476 (OR=1.8; p=2E-08) and LOC100130298 rs142143628 (OR=4.5; p=4.4E-08); all three SNPs validated using internal cross-validation, parametric bootstrap and meta-analysis methods. LEMD3 rs138916004 and LOC100130298 rs142143628 are only present in Africans (1000G data). LEMD3 showed a significant differential expression in both NCBI Gene Expression Omnibus (GEO) and the Mayo Clinic gene expression data, LOC100130298 showed a significant differential expression only in the GEO expression data, and LY86 showed a significant differential expression only in the Mayo expression data. LEMD3 encodes for an antagonist of TGF-ß-induced cell proliferation arrest. LY86 encodes for MD-1 which down-regulates the pro-inflammatory response to lipopolysaccharide; LY86 variation was previously associated with VTE in white women; LOC100130298 is a non-coding RNA gene with unknown regulatory activity in gene expression and epigenetics.

Reasons for the persistent incidence of venous thromboembolism.

Reasons for trends in venous thromboembolism (VTE) incidence are uncertain. It was our objective to determine VTE incidence trends and risk factor prevalence, and estimate population-attributable risk (PAR) trends for each risk factor. In a population-based cohort study of all residents of Olmsted County, Minnesota from 1981-2010, annual incidence rates were calculated using incident VTE cases as the numerator and age- and sex-specific Olmsted County population estimates as the denominator. Poisson regression models were used to assess the relationship of crude incidence rates to year of diagnosis, age at diagnosis, and sex. Trends in annual prevalence of major VTE risk factors were estimated using linear regression. Poisson regression with time-dependent risk factors (person-years approach) was used to model the entire population of Olmsted County and derive the PAR. The age- and sex-adjusted annual VTE incidence, 1981-2010, did not change significantly. Over the time period, 1988-2010, the prevalence of obesity, surgery, active cancer and leg paresis increased. Patient age, hospitalisation, surgery, cancer, trauma, leg paresis and nursing home confinement jointly accounted for 79 % of incident VTE; obesity accounted for 33 % of incident idiopathic VTE. The increasing prevalence of obesity, cancer and surgery accounted in part for the persistent VTE incidence. The PAR of active cancer and surgery, 1981-2010, significantly increased. In conclusion, almost 80 % of incident VTE events are attributable to known major VTE risk factors and one-third of incident idiopathic VTE events are attributable to obesity. Increasing surgery PAR suggests that concurrent efforts to prevent VTE may have been insufficient.

Risk factors for venous thromboembolism after acute trauma: A population-based case-cohort study.

BACKGROUND: Predictors of venous thromboembolism (VTE) after trauma are uncertain. OBJECTIVE: To identify independent predictors of VTE after acute trauma. METHODS: Using Rochester Epidemiology Project (REP) resources, we identified all Olmsted County, MN residents with objectively-diagnosed incident VTE within 92days after hospitalization for acute trauma over the 18-year period, 1988-2005. We also identified all Olmsted County residents hospitalized for acute trauma over this time period and chose one to two residents frequency-matched to VTE cases on sex, event year group and ICD-9-CM trauma code predictive of surgery. In a case-cohort study, demographic, baseline and time-dependent characteristics were tested as predictors of VTE after trauma using Cox proportional hazards modeling. RESULTS: Among 200 incident VTE cases, the median (interquartile range) time from trauma to VTE was 18 (6, 41) days. Of these, 62% cases developed VTE after hospital discharge. In a multiple variable model including 370 cohort members, patient age at injury, male sex, increasing injury severity as reflected by the Trauma Mortality Prediction Model (TMPM) Mortality Score, immobility prior to trauma, soft tissue leg injury, and prior superficial vein thrombosis were independent predictors of VTE (C-statistic=0.78). CONCLUSIONS: We have identified clinical characteristics which can identify patients at increased risk for VTE after acute trauma, independent of surgery. Almost two thirds of all incident VTE events occurred after initial hospital discharge (18day median time from trauma to VTE) which questions current practice of not extending VTE prophylaxis beyond hospital discharge.

Periprocedural Anticoagulation Management of Patients with Thrombophilia.

BACKGROUND: Appropriate periprocedural management of the chronically anticoagulated patient with an inherited or acquired thrombophilia is uncertain. The objective of this study was to test "thrombophilia" as a potential predictor of the 3-month cumulative incidence of thromboembolism and major bleeding among chronically anticoagulated patients undergoing an invasive procedure. METHODS: In a prospective cohort study, consecutive chronically anticoagulated patients referred to the Mayo Thrombophilia Center for standardized periprocedural anticoagulation management who had venous thromboembolism and complete thrombophilia testing were categorized as "severe," "non-severe," or "no identifiable" thrombophilia. The 3-month cumulative incidence rates of thromboembolism, bleeding, and death were estimated using the Kaplan-Meier product limit method. RESULTS: Among 362 patients with complete thrombophilia testing, 165 (46%) had a defined thrombophilia; 76 patients had severe thrombophilia, mainly due to antiphospholipid syndrome (66%). Half of the patients in each of the 3 groups received pre- and postprocedure heparin. During follow-up, there were no thromboembolic events, rare major bleeding events (1% for each group), and 4 deaths. Due to the very low event rates for each of these outcomes, Cox proportional hazard modeling could not be performed. CONCLUSIONS: Periprocedural event rates were low irrespective of thrombophilia status. Inherited or acquired thrombophilia was not a predictor of thromboembolism, major bleeding, or mortality after temporary interruption of chronic anticoagulation for an invasive procedure.

Direct Medical Costs Attributable to Cancer-Associated Venous Thromboembolism: A Population-Based Longitudinal Study.

PURPOSE: The purpose of this study is to estimate medical costs attributable to venous thromboembolism among patients with active cancer. METHODS: In a population-based cohort study, we used Rochester Epidemiology Project (REP) resources to identify all Olmsted County, Minn. residents with incident venous thromboembolism and active cancer over the 18-year period, 1988-2005 (n = 374). One Olmsted County resident with active cancer without venous thromboembolism was matched to each case on age, sex, cancer diagnosis date, and duration of prior medical history. Subjects were followed forward in REP provider-linked billing data for standardized, inflation-adjusted direct medical costs from 1 year prior to index (venous thromboembolism event date or control-matched date) to the earliest of death, emigration from Olmsted County, or December 31, 2011, with censoring on the shortest follow-up to ensure a similar follow-up duration for each case-control pair. We used generalized linear modeling to predict costs for cases and controls and bootstrapping methods to assess uncertainty and significance of mean adjusted cost differences. Outpatient drug costs were not included in our estimates. RESULTS: Adjusted mean predicted costs were 1.9-fold higher for cases ($49,351) than for controls ($26,529) (P < .001) from index to up to 5 years post index. Cost differences between cases and controls were greatest within the first 3 months (mean difference = $13,504) and remained significantly higher from 3 months to 5 years post index (mean difference = $12,939). CONCLUSIONS: Venous thromboembolism-attributable costs among patients with active cancer contribute a substantial economic burden and are highest from index to 3 months, but may persist for up to 5 years.

Risk factors for incident venous thromboembolism in active cancer patients: A population based case-control study.

BACKGROUND: Independent risk factors for cancer-associated incident venous thromboembolism (VTE) and their magnitude of risk are not fully characterized. AIM: To identify non-cancer and cancer-specific risk factors for cancer-associated incident VTE. METHODS: In a population-based retrospective case-control study, we used Rochester Epidemiology Project and Mayo Clinic Cancer Registry resources to identify all Olmsted County, MN residents with active cancer-associated incident VTE, 1973-2000 (cases; n=570) and 1-3 residents with active cancer matched to each case on age, sex, date and duration of active cancer (controls; n=604). Using conditional logistic regression, we tested cancer and non-cancer characteristics for an association with VTE, including a cancer site VTE risk score. RESULTS: In the multivariable model, higher cancer site VTE risk score (OR=1.4 per 2-fold increase), cancer stage≥2 (OR=2.2), liver metastasis (OR=2.7), chemotherapy (OR=1.8) and progesterone use (OR=2.1) were independently associated with VTE, as were BMI<18.5kg/m(2) (OR=1.9) or ≥35kg/m(2) (OR=4.0), hospitalization (OR=7.9), nursing home confinement (OR=4.7), central venous (CV) catheter (OR=8.5) and any recent infection (OR=1.7). In a subgroup analysis, platelet count≥350×10(9)/L at time of cancer diagnosis was marginally associated with VTE (OR=2.3, p=0.07). CONCLUSION: Cancer site, cancer stage≥2, liver metastasis, chemotherapy, progesterone, being underweight or obese, hospitalization/nursing home confinement, CV catheter, and infection are independent risk factors for incident VTE in active cancer patients.

The epidemiology of venous thromboembolism.

Venous thromboembolism (VTE) is categorized by the U.S. Surgeon General as a major public health problem. VTE is relatively common and associated with reduced survival and substantial health-care costs, and recurs frequently. VTE is a complex (multifactorial) disease, involving interactions between acquired or inherited predispositions to thrombosis and VTE risk factors, including increasing patient age and obesity, hospitalization for surgery or acute illness, nursing-home confinement, active cancer, trauma or fracture, immobility or leg paresis, superficial vein thrombosis, and, in women, pregnancy and puerperium, oral contraception, and hormone therapy. Although independent VTE risk factors and predictors of VTE recurrence have been identified, and effective primary and secondary prophylaxis is available, the occurrence of VTE seems to be relatively constant, or even increasing.

Longitudinal effects of menopausal hormone treatments on platelet characteristics and cell-derived microvesicles.

Activated platelets serve as a catalyst for thrombin generation and a source of vasoactive and mitogenic factors affecting vascular remodeling. Oral menopausal hormone treatments (MHT) may carry greater thrombotic risk than transdermal products. This study compared effects of oral and transdermal MHT on platelet characteristics, platelet proteins, and platelet-derived microvesicles (MV) in recently menopausal women. Platelets and MV were prepared from blood of a subset of women (n = 117) enrolled in the Kronos Early Estrogen Prevention Study prior to and after 48 months of treatment with either oral conjugated equine estrogen (0.45 mg/day), transdermal 17ß-estradiol (50 µg/day), each with intermittent progesterone (200 mg/day for 12 days a month), or placebo pills and patch. Platelet count and expression of platelet P-selectin and fibrinogen receptors were similar across groups. An aggregate measure of 4-year change in vasoactive and mitogenic factors in platelet lysate, by principle component analysis, indicated significantly lower values in both MHT groups compared to placebo. Increases in numbers of tissue factor positive and platelet-derived MV were significantly greater in the transdermal compared to placebo group. MHT was associated with significantly reduced platelet content of vasoactive and mitogenic factors representing a potential mechanism by which MHT may affect vascular remodeling. Various hormonal compositions and doses of MHT could differentially regulate nuclear transcription in bone marrow megakaryocytes and non-genomic pathways in circulating platelets thus determining numbers and characteristics of circulating MV. Thrombotic risk associated with oral MHT most likely involves liver-derived inflammatory/coagulation proteins rather than circulating platelets per se.