Whole-Exome Sequencing Identifies Loci Associated with Blood Cell Traits and Reveals a Role for Alternative GFI1B Splice Variants in Human Hematopoiesis.

Circulating blood cell counts and indices are important indicators of hematopoietic function and a number of clinical parameters, such as blood oxygen-carrying capacity, inflammation, and hemostasis. By performing whole-exome sequence association analyses of hematologic quantitative traits in 15,459 community-dwelling individuals, followed by in silico replication in up to 52,024 independent samples, we identified two previously undescribed coding variants associated with lower platelet count: a common missense variant in CPS1 (rs1047891, MAF = 0.33, discovery + replication p = 6.38 × 10(-10)) and a rare synonymous variant in GFI1B (rs150813342, MAF = 0.009, discovery + replication p = 1.79 × 10(-27)). By performing CRISPR/Cas9 genome editing in hematopoietic cell lines and follow-up targeted knockdown experiments in primary human hematopoietic stem and progenitor cells, we demonstrate an alternative splicing mechanism by which the GFI1B rs150813342 variant suppresses formation of a GFI1B isoform that preferentially promotes megakaryocyte differentiation and platelet production. These results demonstrate how unbiased studies of natural variation in blood cell traits can provide insight into the regulation of human hematopoiesis.

Measuring thrombin generation as a tool for predicting hemostatic potential and transfusion requirements following trauma.

BACKGROUND: Thrombin is the central coagulation protease that activates clotting proteins, triggers platelet aggregation, and converts fibrinogen to fibrin. Relationships between thrombin generation (TG) and clinical outcomes have not been defined following trauma. We hypothesize that TG is predictive of transfusion requirements and patient outcomes. METHODS: Plasma was collected from 406 highest-level activation trauma patients upon admission and 29 healthy donors. Standard coagulation tests were performed, and TG was measured by calibrated automated thrombogram. Mann-Whitney U-tests were used to compare healthy versus trauma patients, and subgroup analyses were used to compare hypocoagulable versus nonhypocoagulable patients. Hypocoagulability was determined by area under the receiver operating characteristic curve analysis and was defined as peak TG of less than 250 nM. Multiple logistic regressions were used to assess the ability of TG to predict massive transfusion and mortality. RESULTS: The median (interquartile range) age was 39 years (28-52 years), with an Injury Severity Score (ISS) of 17 (9-26). The trauma patients had greater TG (peak, 316.2 nM [270.1-355.5 nM]) compared with the healthy controls (124.6 nM [91.1-156.2 nM]), p < 0.001. The overall rate of hypocoagulability was 17%. The patients with peak TG of less than 250 nM were more severely injured (ISS, 25 [13-30] vs. 16 [9-25], p = 0.003); required more transfusions of red blood cells (p = 0.02), plasma (p = 0.003), and platelets (p = 0.006); had fewer hospital-free days (p = 0.001); and had increased mortality (10% vs. 3% at 24 hours, p = 0.006, and 29% vs. 11% at 30 days, p = 0.0004). Peak TG of less than 250 nM was predictive of massive transfusion (odds ratio, 4.18; p = 0.01) and 30-day mortality (odds ratio, 2.78; p = 0.02). Finally, peak TG was inversely correlated with standard coagulation tests. CONCLUSION: While the physiologic response to injury is to upregulate plasma procoagulant activity, the patients with reduced TG required more transfusions and had poorer outcomes. Measuring TG may provide an exquisitely sensitive tool for detecting disturbances in the enzymatic phases of coagulation in critically injured patients. LEVEL OF EVIDENCE: Prognostic/epidemiologic study, level III.

Never-frozen liquid plasma blocks endothelial permeability as effectively as thawed fresh frozen plasma.

BACKGROUND: Thawed fresh frozen plasma (TP) is a preferred plasma product for resuscitation but can only be used for up to 5 days after thawing. Never-frozen, liquid plasma (LQP) is approved for up to 26 days when stored at 1°C to 6°C. We have previously shown that TP repairs tumor necrosis factor α (TNF-α)-induced permeability in human endothelial cells (ECs). We hypothesized that stored LQP repairs permeability as effectively as TP. METHODS: Three single-donor LQP units were pooled. Aliquots were frozen, and samples were thawed on Day 0 (TP0) then refrigerated for 5 days (TP5). The remaining LQP was kept refrigerated for 28 days, and aliquots were analyzed every 7 days. The EC monolayer was stimulated with TNF-α (10 ng/mL), inducing permeability, followed by a treatment with TP0, TP5, or LQP aged 0, 7, 14, 21, and 28 days. Permeability was measured by leakage of fluorescein isothiocyanate-dextran through the EC monolayer. Hemostatic profiles of samples were evaluated by thrombogram and thromboelastogram. Statistical analysis was performed using two-way analysis of variance, with p < 0.05 deemed significant. RESULTS: TNF-α increased permeability of the EC monolayer twofold compared with medium control. There was a significant decrease in permeability at 0, 7, 14, 21, and 28 days when LQP was used to treat TNF-α-induced EC monolayers (p < 0.001). LQP was as effective as TP0 and TP5 at reducing permeability. Stored LQP retained the capacity to generate thrombin and form a clot. CONCLUSION: LQP corrected TNF-α-induced EC permeability and preserved hemostatic potential after 28 days of storage, similar to TP stored for 5 days. The significant logistical benefit (fivefold) of prolonged LQP storage improves the immediate availability of plasma as a primary resuscitative fluid for bleeding patients.

Waiver of consent in noninterventional, observational emergency research: the PROMMTT experience.

BACKGROUND: In the PRospective Observational Multicenter Major Trauma Transfusion (PROMMTT) study, waiver of consent was used because previous literature reported low response rates and subsequent bias. The goal of this article was to examine the rationale and tradeoffs of using waiver of consent in PROMMTT. METHODS: PROMMTT enrolled trauma patients receiving at least 1 U of red blood cells within 6 hours after admission at 10 US Level 1 trauma centers. Local institutional review boards (IRBs) from all sites approved the study. Site 8 was required by their IRB to attempt consent but was allowed to retain data on patients unable to be consented. RESULTS: Of 121 subjects enrolled at Site 8, 55 consents were obtained (46%), and no patient or legally authorized representative refused to give consent. Of the patients, 36 (30%) died, and 6 (5%) were discharged before consent could be attempted. Consent was attempted but not possible among 24 patients (20%). Of the 10 clinical sites, 6 of the local IRBs approved collection of residual blood samples, 1 had previous approval to collect timed blood samples under a separate protocol, and 3 reported that their local IRBs would not approve collection of residual blood under a waiver of consent. CONCLUSION: Waiver of consent was used in PROMMTT because of the potential adverse impact of consent refusals; however, there were no refusals. If the IRB for Site 8 had required withdrawal of patients unable to consent and destruction of their data, a serious bias would likely have been introduced. Other tradeoffs included a reduction in sites participating in residual blood collection and a smaller than expected amount of residual blood collected among sites operating under a waiver of consent. Noninterventional emergency research studies should consider these potential tradeoffs carefully before deciding whether waiver of consent would best achieve the goals of a study.

Clinical and mechanistic drivers of acute traumatic coagulopathy.

BACKGROUND: Acute traumatic coagulopathy (ATC) occurs after severe injury and shock and is associated with increased bleeding, morbidity, and mortality. The effects of ATC and hemostatic resuscitation on outcome are not well-explored. The PRospective Observational Multicenter Major Trauma Transfusion (PROMMTT) study provided a unique opportunity to characterize coagulation and the effects of resuscitation on ATC after severe trauma. METHODS: Blood samples were collected upon arrival on a subset of PROMMTT patients. Plasma clotting factor levels were prospectively assayed for coagulation factors. These data were analyzed with comprehensive PROMMTT clinical data. RESULTS: There were 1,198 patients with laboratory results, of whom 41.6% were coagulopathic. Using international normalized ratio of 1.3 or greater, 41.6% of patients (448) were coagulopathic, while 20.5% (214) were coagulopathic using partial thromboplastin time of 35 or greater. Coagulopathy was primarily associated with a combination of an Injury Severity Score (ISS) of greater than 15 and a base deficit (BD) of less than -6 (p < 0.05). Regression modeling for international normalized ratio-based coagulopathy shows that prehospital crystalloid (odds ratio [OR], 1.05), ISS (OR, 1.03), Glasgow Coma Scale (GCS) score (OR, 0.93), heart rate (OR, 1.08), systolic blood pressure (OR, 0.96), BD (OR, 0.92), and temperature (OR, 0.84) were significant predictors of coagulopathy (all p < 0.03). A subset of 165 patients had blood samples collected and coagulation factor analysis performed. Elevated ISS and BD were associated with elevation of aPC and depletion of factors (all p < 0.05). Reductions in factors I, II, V, VIII and an increase in aPC drive ATC (all p < 0.04). Similar results were found for partial thromboplastin time-defined coagulopathy. CONCLUSION: ATC is associated with the depletion of factors I, II, V, VII, VIII, IX, and X and is driven by the activation of the protein C system. These data provide additional mechanistic understanding of the drivers of coagulation abnormalities after injury. Further understanding of the drivers of ATC and the effects of resuscitation can guide factor-guided resuscitation and correction of coagulopathy after injury.

The prospective, observational, multicenter, major trauma transfusion (PROMMTT) study: comparative effectiveness of a time-varying treatment with competing risks.

OBJECTIVE: To relate in-hospital mortality to early transfusion of plasma and/or platelets and to time-varying plasma:red blood cell (RBC) and platelet:RBC ratios. DESIGN: Prospective cohort study documenting the timing of transfusions during active resuscitation and patient outcomes. Data were analyzed using time-dependent proportional hazards models. SETTING: Ten US level I trauma centers. PATIENTS: Adult trauma patients surviving for 30 minutes after admission who received a transfusion of at least 1 unit of RBCs within 6 hours of admission (n = 1245, the original study group) and at least 3 total units (of RBCs, plasma, or platelets) within 24 hours (n = 905, the analysis group). MAIN OUTCOME MEASURE: In-hospital mortality. RESULTS: Plasma:RBC and platelet:RBC ratios were not constant during the first 24 hours (P < .001 for both). In a multivariable time-dependent Cox model, increased ratios of plasma:RBCs (adjusted hazard ratio = 0.31; 95% CI, 0.16-0.58) and platelets:RBCs (adjusted hazard ratio = 0.55; 95% CI, 0.31-0.98) were independently associated with decreased 6-hour mortality, when hemorrhagic death predominated. In the first 6 hours, patients with ratios less than 1:2 were 3 to 4 times more likely to die than patients with ratios of 1:1 or higher. After 24 hours, plasma and platelet ratios were unassociated with mortality, when competing risks from nonhemorrhagic causes prevailed. CONCLUSIONS: Higher plasma and platelet ratios early in resuscitation were associated with decreased mortality in patients who received transfusions of at least 3 units of blood products during the first 24 hours after admission. Among survivors at 24 hours, the subsequent risk of death by day 30 was not associated with plasma or platelet ratios.

An emergency department thawed plasma protocol for severely injured patients.

IMPORTANCE: In an effort to expedite delivery of plasma for patients requiring massive transfusions, US medical centers began keeping thawed plasma (TP) in their blood banks (BBs), markedly reducing time to release of plasma; however, the time to transfusion was still excessively long. OBJECTIVE: To expedite delivery and transfusion of TP through implementation of an emergency department (ED) protocol. DESIGN AND SETTING: Retrospective cohort study in an American College of Surgeons-verified level I trauma center. PARTICIPANTS: Using the Trauma Registry of the American College of Surgeons database, we evaluated all adult trauma patients admitted from June 1, 2009, through August 31, 2010, who arrived directly from the scene, were the institution's highest level trauma activation, and received at least 1 U of red blood cells and 1 U of plasma in the first 6 hours after admission. The protocol was initiated in February 2010 by giving 4 U of AB plasma to patients in the ED. Patients were then divided into 2 groups: those admitted 8 months before (TP-BB) and 8 months after implementing TP location change (TP-ED). MAIN OUTCOME MEASURES: Primary outcome was time to first unit of plasma. Secondary outcomes included 24-hour blood use and 24-hour and 30-day mortality. RESULTS: A total of 294 patients met the study criteria (130 in the TP-BB group and 164 in the TP-ED). Although the patient demographics were similar, TP-ED patients had greater anatomical injury (median Injury Severity Score, 18 vs 25; P = .02) and more physiologic disturbances (median weighted Revised Trauma Score, 6.81 vs 3.83; P = .008). The TP-ED patients had a shorter time to first plasma transfusion (89 vs 43 minutes, P < .001). The TP-ED protocol was associated with a reduction in 24-hour transfusion of RBCs (P = .04), plasma (P = .04), and platelets (P < .001). Logistic regression identified TP-ED as an independent predictor of decreased 30-day mortality (odds ratio, 0.43; 95% CI, 0.194-0.956; P = .04). CONCLUSIONS: We demonstrated that implementation of an ED-TP protocol expedites transfusion of plasma to severely injured patients. This approach is associated with a reduction in overall blood product use and a 60% decreased odds in 30-day mortality.

Better hemostatic profiles of never-frozen liquid plasma compared with thawed fresh frozen plasma.

BACKGROUND: Immediate use of thawed fresh frozen plasma (FFP) when resuscitating hemorrhagic shock patients has become more common. According to the AABB (formerly known as American Association of Blood Banks), FFP is the preferred product that can be used up to 5 days after thawing. However, limited data exist on the clinical use and hemostatic profiles of Food and Drug Administration-approved liquid plasma (LQP), which can be stored at 1 °C to 6 °C for up to 26 days. We characterized changes in LQP hemostatic potential during 26 days of cold storage. METHODS: Ten FFP and 10 LQP single-donor units, matched by sex and blood group, were analyzed. FFP was thawed and kept refrigerated for 5 days and LQP for 26 days. Plasma samples were evaluated at Days 0 and 5 for thawed plasma (TP) and 0, 5, 10, 20, and 26 for LQP, by thrombelastography, thrombogram, platelet counts, platelet microparticles, clotting factors, and natural coagulation inhibitors. RESULTS: LQP had a better capacity to form a clot and generate thrombin compared with TP. LQP's hemostatic potential, expressed as endogenous thrombin potential (total amount of thrombin [nM] formed over time [minute]), initially exceeded that of TP (1,425 vs. 1,184, p < 0.05) but decreased to levels similar to TP by Day 26 (1,201 vs. 1,103, p = 0.15). Significantly higher platelet microparticles were found in LQP on Day 26 compared with those in LQP on Day 0 (23.6 x 10(9)/L vs. 3 x 10(9)/L, p < 0.001) or those in TP on Day 5 (2.8 x 10(9)/L). By Day 26, the majority of clotting factors and inhibitors retained more than 88% of their initial activities in LQP, with the few exceptions of factors well known to be unstable. CONCLUSION: The hemostatic profiles of LQP were better and sustained five times longer than the more commonly used TP, indicating that never-frozen plasma can be considered for use in the United States in trauma patients requiring immediate plasma resuscitation.

Mechanistic determinates of the acute coagulopathy of trauma (ACoT) in patients requiring emergency surgery.

INTRODUCTION: The development of acute coagulopathy of trauma (ACoT) is associated with a significant increase in mortality. However, the contributory mechanisms behind ACoT have yet to be clearly defined. The purpose of this study was to evaluate the influence of multiple variables, including base deficit and injury severity, on development of ACoT within a subset of critically ill trauma patients. METHODS: A retrospective review of all trauma laparotomies between 01/2004-12/2009 was performed. ACoT (+) was defined as an arrival INR ≥1.5, ACoT (-) defined as INR<1.5. Univariate and multivariate analyses were performed. RESULTS: Of 1218 patients, 337 (27%) were ACoT (+) and 881 (73%) were ACoT (-) upon presentation. Groups were similar in demographics, ED fluid administration, GCS scores, and admission temperatures. Admission base deficit (8.5 vs. 4, p<0.001) and ISS (median 25 vs. 16, p<0.001) were higher in the ACoT (+) group, as were intra-operative RBC (median 4 vs. 0 U) and plasma (3 vs. 0 U) transfusions; both p<0.001. Multiple-linear regression revealed INR values were independently associated with arrival base deficit and pre-hospital fluid volumes (both p<0.001). On logistic regression, the development of ACoT (+) was associated with base deficit (OR 0.92, p=0.013) as well as ISS (OR 1.05, p<0.001). However, blunt mechanism alone was not an independent predictor of ACoT. CONCLUSION: The current study revealed that ACoT is independently associated with both shock (base deficit) and tissue injury. Additionally, tissue injury is a significant contributor to the development of early ACoT regardless of blunt or penetrating mechanism.

Hyperfibrinolysis at admission is an uncommon but highly lethal event associated with shock and prehospital fluid administration.

BACKGROUND: Hyperfibrinolysis (HF) has been reported to occur in a range of 2% to 34% of trauma patients. Using rapid thromboelastography (r-TEG), we hypothesized that HF is (1) rarely present at admission on patients with severe injury and (2) associated with crystalloid hemodilution. To further strengthen this hypothesis, we created an in vitro hemodilution model to improve our mechanistic understanding of the early HF. METHODS: The trauma registry was queried for patients who were our highest-level trauma activations and admitted directly from the scene (October 2009-October 2010). HF was defined as more than 7.5% amplitude reduction 30 minutes after maximal amplitude (LY30). Using r-TEG, we then created an in vitro hemodilution model (0.9% NS) with and without tissue injury (addition of tissue factor and tissue plasminogen activator) to identify crystalloid volumes and injury needed to achieve specific LY30 values. RESULTS: Admission r-TEG values were captured on 1996 consecutive admissions. Only 41 patients (2%) had HF at admission r-TEG. The groups were similar in demographics. Compared with patients without HF, the HF group had more prehospital crystalloid (1.5 vs. 0.5 L), higher median Injury Severity Score (25 vs. 16), greater admission base deficit (20 vs. 2), and higher mortality (76% vs. 10%); all p < 0.001. Controlling for Injury Severity Score and base deficit on arrival, prehospital fluid was associated with a significant increase in likelihood of HF. In fact, each additional liter of crystalloid was associated with a 15% increased odds of HF. The in vitro model found that hemodilution to 15% of baseline and tissue factor + tissue plasminogen activator was required to achieve an LY30 of 50%. CONCLUSION: Although uncommon immediately after injury, HF is associated with prehospital crystalloid administration and shock at admission and is highly lethal. Our in vitro model confirms that tissue injury and significant crystalloid hemodilution result in severe and immediate HF.

Admission rapid thrombelastography predicts development of pulmonary embolism in trauma patients.

BACKGROUND: Injury leads to dramatic disturbances in coagulation with increased risk of bleeding followed by a hypercoagulable state. A comprehensive assessment of these coagulation abnormalities can be measured and described by thrombelastography. The purpose of this study was to identify whether admission rapid-thrombelastography (r-TEG) could identify patients at risk of developing pulmonary embolism (PE) during their hospital stay. METHODS: Patients admitted between September 2009 to February 2011 who met criteria for our highest-level trauma activation and were transported directly from the scene were included in the study. PE defined as clinically suspected and computed tomography angiography confirmed PE. We evaluated r-TEG values with particular attention to the maximal amplitude (mA) parameter that is indicative of overall clot strength. Demographics, vital signs, injury severity, and r-TEG values were then evaluated. In addition to r-TEG values, gender and injury severity score (ISS) were chosen a priori for developing a multiple logistic regression model predicting development of PE. RESULTS: r-TEG was obtained on 2,070 consecutive trauma activations. Of these, 2.5% (53) developed PE, 97.5% (2,017) did not develop PE. Patients in the PE group were older (median age, 41 vs. 33 years, p = 0.012) and more likely to be white (69% vs. 54%, p = 0.036). None of the patients in the PE group sustained penetrating injury (0% vs. 25% in the no-PE group, p < 0.001). The PE group also had admission higher mA values (66 vs. 63, p = 0.050) and higher ISS (median, 31 vs. 19, p = 0.002). When controlling for gender, race, age, and ISS, elevated mA at admission was an independent predictor of PE with an odds ratio of 3.5 for mA > 65 and 5.8 for mA > 72. CONCLUSION: Admission r-TEG mA values can identify patients with an increased risk of in-hospital PE. Further studies are needed to determine whether alternative anticoagulation strategies should be used for these high-risk patients. LEVEL OF EVIDENCE: Prognostic study, level III.

Coordination and management of multicenter clinical studies in trauma: Experience from the PRospective Observational Multicenter Major Trauma Transfusion (PROMMTT) Study.

AIM: Early death due to hemorrhage is a major consequence of traumatic injury. Transfusion practices differ among hospitals and it is unknown which transfusion practices improve survival. This report describes the experience of the PRospective Observational Multicenter Major Trauma Transfusion (PROMMTT) Study Data Coordination Center in designing and coordinating a study to examine transfusion practices at ten Level 1 trauma centers in the US. METHODS: PROMMTT was a multisite prospective observational study of severely injured transfused trauma patients. The clinical sites collected real-time information on the timing and amounts of blood product infusions as well as colloids and crystalloids, vital signs, initial diagnostic and clinical laboratory tests, life saving interventions and other clinical care data. RESULTS: Between July 2009 and October 2010, PROMMTT screened 12,561 trauma admissions and enrolled 1245 patients who received one or more blood transfusions within 6h of Emergency Department (ED) admission. A total of 297 massive transfusions were observed over the course of the study at a combined rate of 5.0 massive transfusion patients/week. CONCLUSION: PROMMTT is the first multisite study to collect real-time prospective data on trauma patients requiring transfusion. Support from the Department of Defense and collaborative expertise from the ten participating centers helped to demonstrate the feasibility of prospective trauma transfusion studies. The observational data collected from this study will be an invaluable resource for research in trauma surgery and it will guide the design and conduct of future randomized trials.

The ARIC carotid MRI study of blood cellular markers: an inverse association of monocyte myeloperoxidase content with peripheral arterial disease.

We evaluated the association of blood monocyte and platelet activation markers with the risk of peripheral artery disease (PAD) in a multicenter study of atherosclerosis among African American and Caucasian patients. Flow cytometric analysis of blood cells was performed in 1791 participants (209 cases with PAD and 1582 noncases) from the cross-sectional Atherosclerosis Risk in Communities Carotid Magnetic Resonance Imaging ([MRI] ARIC Carotid MRI) Study to assess platelet glycoproteins IIb and IIIa, P-selectin, CD40 ligand, platelet-leukocyte aggregates, monocyte lipopolysaccharide receptor, toll-like receptors (TLRs) 2 and 4, P-selectin glycoprotein ligand 1, cyclooxygenase 2, and myeloperoxidase. Multivariate regression analyses evaluated the association of cellular markers with the risk of PAD. After adjusting for age, race, and gender, platelet CD40L, and monocyte myeloperoxidase (mMPO) levels were significantly lower (P < .001), and monocyte TLR-4 levels were higher (P = .03) in patients with PAD. With additional adjustments for conventional risk factors, mMPO remained inversely and independently associated with the risk of PAD (odds ratio [OR]: 0.35, P = .01).

Associations between dietary patterns and flow cytometry-measured biomarkers of inflammation and cellular activation in the Atherosclerosis Risk in Communities (ARIC) Carotid Artery MRI Study.

BACKGROUND: Specific foods and overall dietary patterns are associated with soluble biomarkers of systemic inflammation and endothelial activation. However, no large epidemiological studies have evaluated relationships between such dietary factors and cell-specific markers of activation and inflammation as measured by flow cytometry. METHODS: Cell aggregates and multiple platelet and leukocyte markers were quantified by flow cytometry in fresh whole blood from 1101 white adults participating in the Carotid Artery MRI Study, a subset of the larger Atherosclerosis Risk in Communities (ARIC) Study. Two dietary patterns ("Healthy" and "Western") were empirically derived via principal components analysis using data collected by food frequency questionnaire. Cross-sectional associations between dietary patterns and flow cytometry-measured biomarkers were evaluated, adjusting for demographics and lifestyle factors, including medications use. RESULTS: After multivariable adjustment, monocyte lipopolysaccharide receptor (CD14), monocyte toll-like receptor-2, and platelet glycoprotein IIb (CD41) showed inverse associations with the Healthy dietary pattern (p=0.01, 0.04, and 0.01, respectively). In contrast, the Western dietary pattern was positively associated with CD41 and platelet-granulocyte aggregates (p=0.01 and 0.04, respectively). Independent of other dietary factors, alcohol consumption was inversely associated with levels of pan-leukocyte marker (CD45), P-selectin (CD62P) on PLA1 and on PLA2 platelets, and platelet-monocyte, platelet-granulocyte, and platelet-lymphocyte aggregates. CONCLUSION: Dietary patterns and alcohol intake were each cross-sectionally associated with select markers of cellular activation and inflammation measured by flow cytometry. These data are consistent with the hypothesis that holistic measures of dietary intake are associated with inflammation.

Hypercoagulable states and strokes.

Several hematologic disorders and hemostatic defects increase risk of ischemic stroke. A common feature of these disorders is the creation of a prothrombotic state, now commonly referred to as "hypercoagulable state." Hematologic diseases such as essential thrombocythemia, polycythemia vera, and thrombotic thrombocytopenic purpura clearly cause stroke. Effective treatment is now available for these disorders. Association of hemostatic defects with stroke risk is still at the investigational stage. Although a number of factors such as soluble thrombomodulin, fibrinogen, factor VIII, von Willebrand factor, and plasminogen activator inhibitor-1 are associated with stroke risk, their predictive values remain unknown. Furthermore, causal relationship has not been established.