Fibrinolytic Variables in Patients with Recurrent Venous Thrombosis: a Prospective Cohort Study

Overall haemostatic potential assay for prediction of outcomes in venous and arterial thrombosis and thrombo-inflammatory diseases

Thromboembolic diseases including arterial and venous thrombosis are common causes of morbidity and mortality globally. Thrombosis frequently recurs and can also complicate many inflammatory conditions through the process of 'thrombo-inflammation,' as evidenced during the COVID-19 pandemic. Current candidate biomarkers for thrombosis prediction, such as D-dimer, have poor predictive efficacy. This limits our capacity to tailor anticoagulation duration individually and may expose lower risk individuals to undue bleeding risk. Global coagulation assays, such as the Overall Haemostatic Potential (OHP) assay, that investigate fibrin generation and fibrinolysis, may provide a more accurate and functional assessment of hypercoagulability. We present a review of fibrin's critical role as a central modulator of thrombotic risk. The results of our studies demonstrating the OHP assay as a predictive biomarker in venous thromboembolism, chronic renal disease, diabetes mellitus, post-thrombotic syndrome, and COVID-19 are discussed. As a comprehensive and global measurement of fibrin generation and fibrinolytic capacity, the OHP assay may be a valuable addition to future multi-modal predictive tools in thrombosis.

Overall haemostatic potential (OHP) assay can risk stratify for venous thromboembolism recurrence in anticoagulated patients

Assessing the risk of recurrent venous thromboembolism (VTE), particularly when patients are anticoagulated, remains a major challenge largely due to the lack of biomarkers. Blood was sampled from adult VTE patients recruited between January 2018 and September 2020, while receiving therapeutic anticoagulation. Results were compared to 144 healthy subjects (34.7% male, median age 42 years). Overall haemostatic potential (OHP) assay, a spectrophotometric assay, was performed on platelet-poor plasma, in which fibrin formation (triggered by small amounts of thrombin (overall coagulation potential, OCP)) and fibrinolysis (by the addition of thrombin and tissue plasminogen activator (OHP)) are simultaneously measured. Results were obtained from 196 patients (52.6% male, mean age 57.1 years). Compared to healthy subjects, VTE patients displayed significantly higher OCP (39.6 vs 34.5 units, p < 0.001) and OHP (9.3 vs 6.4 units, p < 0.001) as well as lower overall fibrinolytic potential (75.6 v s81.1%, p < 0.001). All 16 VTE recurrences, including 11 unprovoked, occurred above an OCP cut-off of 40^th percentile (recurrence rate 4.32/100 patient-years (100PY), 95% confidence interval (CI) 2.39-7.80, p = 0.002). Of 97 patients who subsequently discontinued anticoagulation, all unprovoked VTE recurrences (n = 9) occurred above the 40^th OCP percentile (recurrence rate 9.10/100PY, 95% CI 4.74-17.49, p = 0.005) and the 40^th OHP percentile (recurrence rate 8.46/100PY, 95% CI 4.40-16.25, p = 0.009). Our pilot study demonstrates that the OHP assay can detect a hypercoagulable and hypofibrinolytic state in anticoagulated VTE patients and may be able to risk stratify VTE recurrence, allowing for more individualised decision on long-term anticoagulation. Further larger prospective studies are required.

Assessing Plasmin Generation in Health and Disease

Fibrinolysis is an important process in hemostasis responsible for dissolving the clot during wound healing. Plasmin is a central enzyme in this process via its capacity to cleave fibrin. The kinetics of plasmin generation (PG) and inhibition during fibrinolysis have been poorly understood until the recent development of assays to quantify these metrics. The assessment of plasmin kinetics allows for the identification of fibrinolytic dysfunction and better understanding of the relationships between abnormal fibrin dissolution and disease pathogenesis. Additionally, direct measurement of the inhibition of PG by antifibrinolytic medications, such as tranexamic acid, can be a useful tool to assess the risks and effectiveness of antifibrinolytic therapy in hemorrhagic diseases. This review provides an overview of available PG assays to directly measure the kinetics of plasmin formation and inhibition in human and mouse plasmas and focuses on their applications in defining the role of plasmin in diseases, including angioedema, hemophilia, rare bleeding disorders, COVID-19, or diet-induced obesity. Moreover, this review introduces the PG assay as a promising clinical and research method to monitor antifibrinolytic medications and screen for genetic or acquired fibrinolytic disorders.

Individualised Risk Assessments for Recurrent Venous Thromboembolism: New Frontiers in the Era of Direct Oral Anticoagulants

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality and is associated with high recurrence rates. The introduction of direct oral anticoagulants (DOACs) in the 2010s has changed the landscape of VTE management. DOACs have become the preferred anticoagulant therapy for their ease of use, predictable pharmacokinetics, and improved safety profile. Increasingly, guidelines have recommended long term anticoagulation for some indications such as following first unprovoked major VTE, although an objective individualised risk assessment for VTE recurrence remains elusive. The balance of preventing VTE recurrence needs to be weighed against the not insignificant bleeding risk, which is cumulative with prolonged use. Hence, there is a need for an individualised, targeted approach for assessing the risk of VTE recurrence, especially in those patients in whom the balance between benefit and risk of long-term anticoagulation is not clear. Clinical factors alone do not provide the level of discrimination required on an individual level. Laboratory data from global coagulation assays and biomarkers may provide enhanced risk assessment ability and are an active area of research. A review of the prediction models and biomarkers for assessing VTE recurrence risk is provided, with an emphasis on contemporary developments in the era of DOACs and global coagulation assays.

Fibrinolysis and Inflammation in Venous Thrombus Resolution

Clinical observations and accumulating laboratory evidence support a complex interplay between coagulation, inflammation, innate immunity and fibrinolysis in venous thromboembolism (VTE). VTE, which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), and the subsequent complications of post-thrombotic syndrome (PTS), are significant causes of morbidity and mortality in patients. Clinical risk factors for VTE include cancer, major trauma, surgery, sepsis, inflammatory bowel disease, paralysis, prolonged periods of immobility, and aging. Abnormalities in venous blood flow or stasis initiates the activation of endothelial cells, and in concert with platelets, neutrophils and monocytes, propagates VTE in an intact vein. In addition, inflammatory cells play crucial roles in thrombus recanalization and restoration of blood flow via fibrinolysis and vascular remodeling. Faster resolution of the thrombus is key for improved disease prognosis. While in the clinical setting, anticoagulation therapy is successful in preventing propagation of venous thrombi, current therapies are not designed to inhibit inflammation, which can lead to the development of PTS. Animal models of DVT have provided many insights into the molecular and cellular mechanisms involved in the formation, propagation, and resolution of venous thrombi as well as the roles of key components of the fibrinolytic system in these processes. Here, we review the recent advances in our understanding of fibrinolysis and inflammation in the resolution of VTE.

Uncertain thrombophilia markers

The development of venous thromboembolism (VTE), which includes deep-vein thrombosis and pulmonary embolism, may be associated with inherited or acquired risk factors that can be measured in plasma or DNA testing. The main inherited thrombophilias include the plasma deficiencies of the natural anticoagulants antithrombin, protein C and S; the gain-of-function mutations factor V Leiden and prothrombin G20210A; some dysfibrinogenaemias and high plasma levels of coagulation factor VIII. Besides these established biomarkers, which usually represent the first-level laboratory tests for thrombophilia screening, a number of additional abnormalities have been less consistently associated with an increased VTE risk. These uncertain causes of thrombophilias will be discussed in this narrative review, focusing on their clinical impact and the underlying pathogenetic mechanisms. Currently, there is insufficient ground to recommend their inclusion within the framework of conventional thrombophilia testing.

Bioactivity-Guided Fractionation of the Traditional Chinese Medicine Resina Draconis Reveals Loureirin B as a PAI-1 Inhibitor

Thrombotic diseases have become a global burden due to morbidity, mortality, and disability. Traditional Chinese medicine has been proven effective in removing blood stasis and promoting blood circulation, but the exact mechanisms remain unclear. Plasminogen activator inhibitor-1 (PAI-1) is a natural inhibitor of tissue-type and urokinase-type plasminogen activators. In this study, we screened four fractions of Resina Draconis (a traditional Chinese medicine) extract for PAI-1 inhibitory activity. Bioactivity-guided purification and chromogenic substrate-based assay led to the identification of loureirin B as the major PAI-1 inhibitor, with an IC₅₀ value of 26.10 μM. SDS-PAGE analysis showed that formation of the PAI-1/uPA complex was inhibited by loureirin B, and the inhibitory effect of loureirin B on PAI-1 was also confirmed by clot lysis assay. In vivo studies showed that loureirin B significantly prolonged the tail bleeding time and reduced the weight and size of arterial thrombus, reduced hydroxyproline level, and partly cured liver fibrosis in mice. Taken together, the results revealed loureirin B as a PAI-1 inhibitor, adding a new pharmacological target for loureirin B and uncovering a novel mechanism underlying the antithrombotic property of Resina Draconis, which might be useful in the treatment of cardiovascular diseases such as thrombosis and fibrosis.

Inhibition of PAI-1 Activity by Toddalolactone as a Mechanism for Promoting Blood Circulation and Removing Stasis by Chinese Herb Zanthoxylum nitidum var. tomentosum

Traditional Chinese medicine has been used to treat a variety of human diseases for many centuries. Zanthoxylum nitidum var. tomentosum is used as an adjuvant to promote blood circulation and remove stasis. However, the mechanisms of improving circulation and other biological activities of Z. nitidum var. tomentosum are still unclear. Plasminogen activator inhibitor-1 (PAI-1) regulates the plasminogen activation system through inhibition of tissue-type and urokinase-type plasminogen activators (tPA and uPA). PAI-1 has been linked to fibrin deposition that evolves into organ fibrosis and atherosclerosis. In the present study, we showed that ethanol extract prepared from Z. nitidum var. tomentosum exhibited PAI-1 inhibitory activity, and identified toddalolactone as the main active component that inhibited the activity of recombinant human PAI-1 with IC₅₀ value of 37.31 ± 3.23 μM, as determined by chromogenic assay, and the effect was further confirmed by clot lysis assay. In vitro study showed that toddalolactone inhibited the binding between PAI-1 and uPA, and therefore prevented the formation of the PAI-1/uPA complex. Intraperitoneal injection of toddalolactone in mice significantly prolonged tail bleeding and reduced arterial thrombus weight in a FeCl₃-induced thrombosis model. In addition, the hydroxyproline level in the plasma and the degree of liver fibrosis in mice were decreased after intraperitoneal injection of toddalolactone in CCl₄-induced mouse liver fibrosis model. Taken together, PAI-1 inhibition exerted by toddalolactone may represent a novel molecular mechanism by which Z. nitidum var. tomentosum manifests its effect in the treatment of thrombosis and fibrosis.

Prolonged clot lysis time increases the risk of a first but not recurrent venous thrombosis

The role of the fibrinolytic system in the development of venous thrombosis (VT) is unclear. We studied the risk of first and recurrent VT associated with reduced fibrinolysis, as measured by clot lysis time (CLT). We also studied the relationship between CLT and thrombin generation to determine if any relationship between CLT and VT was affected by thrombin generation. Analyses were performed in the Thrombophilia Hypercoagulability Environmental risk for Venous Thromboembolism Study, a two-centre population-based case-control study, including 579 patients and 338 controls, with patients followed from the event to determine incidence of recurrent VT. Hypofibrinolysis was associated with a 1·8-fold increased risk of a first VT [95% confidence interval (CI) 1·2-2·7]. Adjustment for sex, age, study location and Endogenous Thrombin Potential (ETP) did not change the result. The risk of VT was 2·9-fold increased when the 90th percentiles of prolonged CLT and high ETP were combined, with the highest risk for unprovoked first events (Odds Ratio = 4·2, 95% CI 1·3-13·5). In the follow-up study the Hazard Ratio for a recurrent VT associated with hypofibrinolysis was 1·5 (95% CI 0·9-2·6). A weak dose response effect was observed in relation to prolongation of CLT and recurrent VT. Although hypofibrinolysis constitutes a risk factor for a first VT, an association with recurrence is, at best, weak.

The Occurrence of Thrombosis in Inflammatory Bowel Disease Is Reflected in the Clot Lysis Profile

BACKGROUND

The occurrence of thromboembolic events (TE) is an important extraintestinal manifestation in patients with inflammatory bowel disease (IBD). The aim of this study was to compare fibrinolysis and clot lysis parameters between (1) patients with IBD and healthy controls and (2) patients with IBD with TE (IBD + TE) and without TE (IBD - TE).

METHODS

One hundred thirteen healthy controls and 202 patients with IBD, of which 84 patients with IBD + TE and 118 patients with IBD - TE, were included in this case-control study. Three clot lysis parameters (area under the curve, 50% clot lysis time, and amplitude) were determined using a clot lysis assay. Plasminogen activator inhibitor 1 (PAI-1) and thrombin activatable fibrinolysis inhibitor concentrations were determined by enzyme-linked immunosorbent assay.

RESULTS

PAI-1 antigen, active PAI-1, and intact thrombin activatable fibrinolysis inhibitor concentrations, as well as 50% clot lysis time and area under the curve, were significantly associated with the presence of IBD (all P < 0.05). The median time between TE and plasma collection was 5.0 (1.8-11.0) years. Comparing IBD + TE versus IBD - TE, active to total PAI-1 ratio (0.36 [0.24-0.61] versus 0.24 [0.13-0.40]), area under the curve (31 [24-49] versus 22 [13-31]), 50% clot lysis time (110 [64-132] versus 95 [70-126] minutes), and amplitude (0.295 [0.222-0.436] versus 0.241 [0.168-0.308]) were significantly higher in IBD + TE (all P <0.05) and remained higher after adjustment for age, gender, C-reactive protein, type of disease, presence of comorbidities, and disease activity.

CONCLUSIONS

Patients with IBD have an altered clot lysis profile compared with healthy controls. Clot lysis parameters differ significantly between patients with IBD with and without a history of TE and should be included in the risk assessment.

High Plasma Levels of D-Dimer Are Independently Associated with a Heightened Risk of Deep Vein Thrombosis in Patients with Intracerebral Hemorrhage

Deep venous thrombosis (DVT) is a complication of stroke. Our aim was to determine whether D-dimer plasma levels at admission could be a risk factor for DVT in Chinese patients with acute intracerebral hemorrhage (ICH). From December 2012 to November 2014, all patients with first-ever acute ICH were included. At baseline, the demographical and clinical data were taken. These patients were assessed for DVT using color Doppler ultrasonography (CDUS) on 15 days after ICH and whenever clinically requested. Multivariate analyses were performed using logistic regression models. Receiver operating characteristic (ROC) curves were used to test the overall predictive accuracy of D-dimer and other markers. In our study, acute ICH was diagnosed in 265 patients and 210 completed a 15-day follow-up and were included in the analysis. Fifty-four (25.7 %) out of the 210 patients were diagnosed as DVT. Plasma D-dimer levels were significantly higher in ICH patients with DVT as compared to those without DVT (P < 0.0001). Multivariate logistic regression analysis adjusted for common risk factors showed that plasma D-dimer levels ≥1.20 mg/L were an independent predictor of DVT [odds ratio (OR) = 12.99, 95 % confidence interval (CI) = 3.17-32.98; P < 0.0001]. With an area under the curve (AUC) of 0.91 (95 % CI = 0.86-0.94), D-dimer showed a significantly greater discriminatory ability to predict DVT as compared with high-sensitivity C-reactive protein (Hs-CRP) (AUC = 0.77, 95 % CI = 0.70-0.82; P < 0.01), homocysteine (HCY) (AUC = 0.75, 95 % CI = 0.70-0.81; P < 0.01), and National Institutes of Health Stroke Scale (NIHSS) score (AUC = 0.80, 95 % CI = 0.72-0.85; P < 0.01). The present study suggested that elevated D-dimer plasma levels were independent predictors for DVT in Chinese patients with ICH.

Fibrinolysis and the control of blood coagulation

Fibrin plays an essential role in hemostasis as both the primary product of the coagulation cascade and the ultimate substrate for fibrinolysis. Fibrinolysis efficiency is greatly influenced by clot structure, fibrinogen isoforms and polymorphisms, the rate of thrombin generation, the reactivity of thrombus-associated cells such as platelets, and the overall biochemical environment. Regulation of the fibrinolytic system, like that of the coagulation cascade, is accomplished by a wide array of cofactors, receptors, and inhibitors. Fibrinolytic activity can be generated either on the surface of a fibrin-containing thrombus, or on cells that express profibrinolytic receptors. In a widening spectrum of clinical disorders, acquired and congenital defects in fibrinolysis contribute to disease morbidity, and new assays of global fibrinolysis now have potential predictive value in multiple clinical settings. Here, we summarize the basic elements of the fibrinolytic system, points of interaction with the coagulation pathway, and some recent clinical advances.

Active PAI-1 as marker for venous thromboembolism: case-control study using a comprehensive panel of PAI-1 and TAFI assays

BACKGROUND

Both activated Thrombin Activatable Fibrinolysis Inhibitor (TAFI) and active Plasminogen Activator Inhibitor-1 (PAI-1) attenuate fibrinolysis and may therefore contribute to the pathophysiology of Venous ThromboEmbolism (VTE). Whether increased TAFI and/or PAI-1 concentrations are associated with VTE is unclear.

OBJECTIVE

To study an association of impaired fibrinolysis and VTE using a comprehensive panel of in-house developed assays measuring intact TAFI, activation peptide of TAFI (AP-TAFI), PAI-1 antigen, endogenous PAI-1:t-PA complex (PAI-1:t-PA) and active PAI-1 levels in 102 VTE patients and in 113 healthy controls (HC).

RESULTS

Active PAI-1 was significantly higher in VTE patients compared to HC (20.9 [9.6-37.8] ng/ml vs. 6.2 [3.5-9.7] ng/ml, respectively). Active PAI-1 was the best discriminator with an area under the ROC curve and 95% confidence interval (AUROC [95%CI]) of 0.84 [0.79-0.90] compared to 0.75 [0.68-0.72] for PAI-1:t-PA, 0.65 [0.58-0.73] for PAI-1 antigen, 0.62 [0.54-0.69] for AP-TAFI and 0.51 [0.44-0.59] for intact TAFI. Using ROC analysis, we defined an optimal cut-off of 12.8 ng/ml for active PAI-1, with corresponding sensitivity of 71 [61-79] % and specificity of 89 [82-94] %. A lack of association with the time between VTE event and sample collection or with the intake of anticoagulant treatment suggests that active PAI-1 levels are sustainable high in VTE patients.

CONCLUSIONS

This case-control study emphasizes the clinical importance of measuring active PAI-1 instead of PAI-1 antigen and identifies active PAI-1 as a potential marker of VTE. Prognostic studies will need to address the clinical significance of active PAI-1 as biomarker.

New combinational assay using soluble fibrin and d-dimer determinations: a promising strategy for identifying patients with suspected venous thromboembolism

Aim

To establish a new and reliable assay for quantification of the soluble fibrin (SF) in combination with that of D-dimer for early diagnosis of venous thromboembolism.

Methods and Samples

The SF assay is based on D-dimer generated after incubation of plasma with tissue-type plasminogen activator (t-PA). SF and standard D-dimer assays, run in blind, were used to test 119 untreated outpatients with clinically suspected deep-vein thrombosis (DVT, 49 patients) or pulmonary embolism (PE, 70 patients) consulting at the emergency unit of the hospital. Thromboses were confirmed by current imaging methods such as ultrasonography, scintigraphy, computed tomographic pulmonary angiography (CTPA) and ventilation/perfusion scan.

Results

SF assay was validated in 270 healthy volunteers [51.8% males; mean age years ± SD: 41±13; age range 19 to 65]. Among these normal plasmas, SF levels were ≤200 ng/mL in 97.8% of them, and 200–250 ng/mL in the remainder [26–46 years old; 50% males]. ROC curves were used to determine the SF cut-off value for plasma SF positivity, which was found to be 300 ng/mL. In patients with suspected venous thromboembolism, SF sensitivities for DVT and PE (92% and 94%, respectively) were comparable to those of D-dimer (96% and 94%), whereas SF specificities (86% and 95%) were higher than those of D-dimer (50% and 54%). Positive-predictive values for SF (89% and 94%) were again higher than those of D-dimer (70% and 65%) in DVT and PE. The amount of circulating SF normalized rapidly after anticoagulant therapy.

Conclusion

Results from this small group of patients suggest that the evaluation of plasma SF, in combination with that of D-dimer, represents a potentially useful tool for the early diagnosis of venous thromboembolism, provided that the patients have not been treated previously by anticoagulants.

The role of urokinase plasminogen activator and plasmin activator inhibitor-1 on vein wall remodeling in experimental deep vein thrombosis

OBJECTIVE

Deep vein thrombosis (DVT) resolution instigates an inflammatory response, resulting in vessel wall damage and scarring. Urokinase-plasminogen activator (uPA) and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), are integral components of the fibrinolytic system, essential for venous thrombosis (VT) resolution. This study determined the vein wall response when exposed to increased and decreased plasmin activity.

METHODS

A mouse inferior vena cava (IVC) ligation model in uPA -/- or PAI-1 -/- and their genetic wild types (B6/SvEv and C57/BL6, respectively) was used to create stasis thrombi, with tissue harvest at either 8 or 21 days. Tissue analysis included gene expression of vascular smooth muscle cells (alpha smooth muscle actin [αSMA], SM22) and endothelial marker (CD31), by real-time polymerase chain reaction, enzyme-linked immunosorbent assay, matrix metalloproteinase (MMP)-2 and -9 activity by zymography, and vein wall collagen by picro-Sirius red histologic analysis. A P < .05 was considered significant.

RESULTS

Thrombi were significantly larger in both 8-day and 21-day uPA -/- as compared with wild type (WT) and were significantly smaller in both 8-day and 21-day PAI-1 -/- as compared with WT. Correspondingly, 8-day plasmin levels were reduced in half in uPA -/- and increased three-fold in PAI-1 -/- when compared with respective WT thrombi (P < .05; n = 5-6). The endothelial marker CD31 was elevated two-fold in PAI-1 -/- mice at 8 days, but reduced 2.5-fold at 21 days in uPA -/- as compared with WT (P = .02; n = 5-6), suggesting less endothelial preservation. Vein wall vascular smooth muscle cell (VSMC) gene expression showed that 8-day and 21-day PAI-1 -/- mice had 2.3- and 3.8-fold more SM22 and 1.8- and 2.3-fold more αSMA expression than respective WT (P < .05; n = 5-7), as well as 1.8-fold increased αSMA (+) cells (P ≤ .05; n = 3-5). No significant difference in MMP-2 or -9 activity was found in the PAI-1 -/- mice compared with WT, while 5.4-fold more MMP-9 was present in 21-day WT than 21-day uPA -/- (P = .03; n = 5). Lastly, collagen was ∼two-fold greater at 8 days in PAI-1 -/- IVC as compared with WT (P = .03; n = 6) with no differences observed in uPA -/- mice.

CONCLUSIONS

In stasis DVT, plasmin activity is critical for thrombus resolution. Divergent vein wall responses occur with gain or loss of plasmin activity, and despite smaller VT, greater vein wall fibrosis was associated with lack of PAI-1.

Failure to lyse venous thrombi because of elevated plasminogen activator Inhibitor 1 (PAI-1) and 4G polymorphism of its promotor genome (The PAI-1/4G Syndrome)

Plasminogen activator Inhibitor 1 (PAI-1) inhibits plasminogen activators leading to decreased fibrinolysis and increased risk of thromboembolic disease (TED). Shifts in PAI-1 promoter genome from normal 5G>5G to 4G>5G or 4G>4G alleles are associated with overexpression of PAI-1. In this study patients with residual venous thrombi were observed to have increased PAI-1 levels and more frequent shifts to 4G alleles. Of the 26, 20 (76.9%) patients with unresolved thrombus had elevated PAI-1 values. 4G genomic shifts were found in 92.9% patients studied. Normal PAI-1 levels were found in 5 patients with 4G polymorphisms. Thus, PAI-1 is often elevated among patients with residual thrombus, with an unexpectedly high prevalence of the 4G polymorphism of the promoter genome. Patients with persistent thrombus should be considered at risk of having constituently increased PAI-1 due to genomic changes in the PAI-1 promoter genome. Hypotheses are proposed to explain those with normal PAI-1, despite having 4G polymorphisms.

Risk assessment for recurrent venous thrombosis

Venous thrombosis is a common disease that frequently recurs. Recurrence can be prevented by anticoagulants, albeit at the cost of bleeding. Thus, assessment of the risk of recurrence is important to balance the risks and benefits of anticoagulation treatment. Many clinical and laboratory risk factors for recurrent venous thrombosis have been established. Nevertheless, prediction of recurrence in an individual patient remains a challenge. Detection of some laboratory markers is associated with only a moderate risk of recurrence, and the relevance of others is not known. Many patients have several risk factors and the effect of combined defects is obscure. Routine screening for these laboratory markers should therefore be abandoned. Risk assessment can be improved by measurement of global markers that encompass the effects of clotting and fibrinolytic disorders. Analysis of preliminary data suggests that risk assessment can also be refined through integration of prothrombotic coagulation changes and clinical risk factors.

Diagnostic algorithm for thrombophilia screening

Thrombophilia screening is aimed at detecting the most frequent and well-defined causes of venous thrombosis, such as activated protein C resistance/factor V Leiden mutation, prothrombin G20210A gene mutation, deficiencies of natural anticoagulants, such as antithrombin, protein C and protein S, the presence of antiphospholipid antibodies, hyperhomocysteinemia and increased factor VIII activity. At this time, thrombophilia screening is not recommended for those possible congenital or acquired risk factors, whose association with increased risk of thrombosis has not been proven sufficiently. Laboratory investigations should include a step-wise approach to the diagnosis of thrombotic disorders with respect to the assays and methods of analysis that are used. The assays recommended for the first diagnostic step of screening should establish, whether the subject has one of the common causes of thrombophilia. If one or more abnormal results are obtained, the second diagnostic step includes the assays recommended for confirmation and/or characterization of the defect. When performing the investigation of thrombophilia, it is important to consider all pre-analytical and other variables that may affect the results of thrombophilia testing, including time of testing, age, gender, liver function, hormonal status, pregnancy or the acute phase response to inflammatory diseases. This is necessary, in order to avoid, any misinterpretation of the results. This review summarizes the current knowledge concerning thrombophilia investigations, with special focus on the diagnostic algorithm regarding patient selection, the assays and methods of analysis used and all the variables that should be considered when employing tests for the diagnosis of thrombophilia.

Effect of the small molecule plasminogen activator inhibitor-1 (PAI-1) inhibitor, PAI-749, in clinical models of fibrinolysis

BACKGROUND

The principal inhibitor of fibrinolysis in vivo is plasminogen activator inhibitor-1 (PAI-1). PAI-749 is a small molecule inhibitor of PAI-1 with proven antithrombotic efficacy in several preclinical models.

OBJECTIVE

To assess the effect of PAI-749, by using an established ex vivo clinical model of thrombosis and a range of complementary in vitro human plasma-based and whole blood-based models of fibrinolysis.

METHODS

In a double-blind, randomized, crossover study, ex vivo thrombus formation was assessed using the Badimon chamber in 12 healthy volunteers during extracorporeal administration of tissue-type plasminogen activator (t-PA) in the presence of PAI-749 or control. t-PA-mediated lysis of plasma clots and of whole blood model thrombi were assessed in vitro. The role of vitronectin was examined by assessing lysis of fibrin clots generated from purified plasma proteins.

RESULTS

There was a dose-dependent reduction in ex vivo thrombus formation by t-PA (P < 0.0001). PAI-749 had no effect on in vitro or ex vivo thrombus formation or fibrinolysis in the presence or absence of t-PA. Inhibition of PAI-1 with a blocking antibody enhanced fibrinolysis in vitro (P < 0.05).

CONCLUSIONS

Despite its efficacy in a purified human system and in preclinical models of thrombosis, the current study suggests that PAI-749 does not affect thrombus formation or fibrinolysis in a range of established human plasma and whole blood-based systems.

Impaired fibrinolysis as a risk factor for Budd-Chiari syndrome

In Budd-Chiari syndrome (BCS), thrombosis develops in the hepatic veins or inferior vena cava. To study the relationship between hypofibrinolysis and BCS, we measured plasma levels of fibrinolysis proteins in 101 BCS patients and 101 healthy controls and performed a plasma-based clot lysis assay. In BCS patients, plasminogen activator inhibitor 1 (PAI-1) levels were significantly higher than in controls (median, 6.3 vs 1.4 IU/mL, P < .001). Thrombin-activatable fibrinolysis inhibitor and plasmin inhibitor levels were lower than in controls (13.8 vs 16.9 μg/mL and 0.91 vs 1.02 U/L, both P < .001). Median plasma clot lysis time (CLT) was 73.9 minutes in cases and 73.0 minutes in controls (P = .329). A subgroup of cases displayed clearly elevated CLTs. A CLT above the 90th or 95th percentile of controls was associated with an increased risk of BCS, with odds ratios of 2.4 (95% confidence interval, 1.1-5.5) and 3.4 (95% confidence interval, 1.2-9.7), respectively. In controls, only PAI-1 activity was significantly associated with CLT. Analysis of single nucleotide polymorphisms of fibrinolysis proteins revealed no significant differences between cases and controls. This case-control study provides the first evidence that an impaired fibrinolytic potential, at least partially caused by elevated PAI-1 levels, is related to the presence of BCS.

Role of selectins and fibrinolysis in VTE

Venous thromboembolism (VTE) accounts for an estimated 900,000 cases of deep venous thrombosis (DVT) and pulmonary embolism (PE) yearly, resulting in approximately 300,000 deaths [1]. For the past 150 years, Virchow's triad has encompassed the elements of venous thrombogenesis, including stasis, changes in the vessel wall, and thrombogenic changes in the blood. However, in the early 1970s, through the work of Gwendylen Stewart, a relationship between thrombosis and inflammation was suggested. In this review, we will address the role of selectins and fibrinolysis in the process of venous thrombogenesis.

Duration of anticoagulation after initial idiopathic venous thrombosis--the swinging pendulum: risk assessment to predict recurrence

Despite considerable advances in the identification of new risk factors for VTE, predicting the risk of recurrence in an individual patient remains a challenge. The impact of many of these risk factors on the recurrence risk is moderate, while the relevance of others is unknown or is regarded controversial. The determination of some markers of thrombophilia either lacks standardization or is too elaborate for routine purposes. Many patients carry more than one risk factor and their combined effect is unknown. Use of global coagulation markers that encompass the effects of clotting and/or fibrinolytic defects may improve risk assessment. In a future step, prothrombotic coagulation alterations need to be integrated with clinical risk factors. Reproducible and simple scoring systems may improve stratification of patients according to their recurrence risk and optimize duration of anticoagulant therapy.

Inherited Thrombophilia

Inherited thrombophilia can be defined as a genetically determined predisposition to the development of thromboembolic complications. Since the discovery of activated protein C resistance in 1993, several additional disorders have been described and, at present, it is possible to identify an inherited predisposition in about 60 to 70% of patients with such complications. These inherited prothrombotic risk factors include qualitative or quantitative defects of coagulation factor inhibitors, increased levels or function of coagulation factors, defects of the fibrinolytic system, altered platelet function, and hyperhomocysteinemia. In this review, the main inherited prothrombotic risk factors are analyzed from epidemiological, laboratory, clinical, and therapeutic points of view. Finally, we discuss the synergism between genetic and acquired prothrombotic risk factors in particular conditions such as childhood and pregnancy.

Mechanisms of Venous Thrombosis and Resolution

Venous thromboembolism is a significant health care problem in the US. In this review, the unique role of inflammation to the venous thrombotic process is emphasized as well as the potential role of abnormalities of fibrinolytic mechanisms to the thrombotic process. Inflammation influences not only thrombogenesis but also thrombus resolution and vein wall remodeling, and these interactions are also discussed. Knowledge of molecular and immunologic mechanisms for venous thrombosis and its resolution should allow for the future development of targeted therapies.

Fibrinolysis and the risk of venous and arterial thrombosis

PURPOSE OF REVIEW

The fibrinolytic system is often regarded as just an innocent bystander in the pathogenesis of venous and arterial thrombosis, while (hyper)coagulation as a risk factor has been studied extensively. In this review, we evaluated studies that investigated the association between fibrinolysis and thrombosis.

RECENT FINDINGS

There is some evidence for an association between impaired overall fibrinolytic activity and increased risk of venous or arterial thrombosis. Plasminogen levels were found not to be related to thrombosis. Plasma levels of tissue-type plasminogen activator were related to arterial thrombosis in a number of studies but not to venous thrombosis. Thrombin activatable fibrinolysis inhibitor levels appeared to be associated with venous thrombosis. Studies on the association between thrombin activatable fibrinolysis inhibitor or plasminogen activator inhibitor-1 and arterial thrombosis had conflicting results.

SUMMARY

Current evidence on an association between fibrinolysis and thrombosis is inconclusive. Although overall assays point to an association, not all individual factors have an association with thrombosis. Most importantly, plasminogen deficiency is not related to thrombosis, which suggests that the fibrinolytic system as a whole is unimportant in the occurrence of thrombosis. Certain components of the fibrinolytic system, however, appear to be involved in processes unrelated to fibrin degradation but related to other processes important in the development of thrombosis.

Evaluation of pre-analytical, demographic, behavioural and metabolic variables on fibrinolysis and haemostasis activation markers utilised to assess hypercoagulability

BACKGROUND

Measurement of some haemostatic factors and products formed during activation of haemostasis seems to be promising in the determination of hypercoagulability.

METHODS

The fibrinolytic variables euglobulin clot lysis time, tissue-type plasminogen activator, plasminogen activator inhibitor-1 and the haemostasis activation markers prothrombin fragment 1+2, thrombin-antithrombin complex and D-dimer were determined in 101 apparently healthy men and women aged 20-92 years (58+/-18 years, mean+/-SD) to establish variability due to several demographic, behavioural and metabolic factors.

RESULTS

None of the fibrinolytic variables were affected by smoking, while tissue-type plasminogen activator antigen was significantly lower in women compared to men. Multiple regression analysis revealed several independent associations between tissue-type plasminogen activator, plasminogen activator inhibitor, body mass index and lipid levels, describing up to 40% of the variance in fibrinolytic variables. For haemostasis activation markers, no gender difference or effect of smoking was observed. Only D-dimer was independently associated with age. The haemostasis activation markers determined proved to be extremely sensitive to blood sampling procedure and were significantly higher in samples obtained by an untrained nurse compared to a trained nurse.

CONCLUSIONS

Fibrinolytic variables are predominantly modulated by age, body mass index and blood lipids, while haemostasis activation markers are mainly un-influenced by these factors.

Endogenous risk factors for deep-vein thrombosis in patients with acute spinal cord injuries

STUDY DESIGN

Case-control study.

AIM OF THE STUDY

Investigate the presence of additional endogenous risk factors of deep-vein thrombosis (DVT).

SETTING

Regional Spinal Unit of Florence, Italy.

METHODS

A total of 43 patients with spinal lesion and a history of DVT during the acute stage of their neurological impairment (Group A) were comprehensively evaluated and the blood concentrations of the following risk factors, that are presumably associated with DVT, were determined: antithrombin III (ATIII), protein C (PC), protein S (PS), factor V Leiden, gene 200210A polymorphism, homocysteine (Hcy), inhibitor of plasminogen activator-1 (PAI-1) and lipoprotein A (LpA). The control group (Group B) consisted of 46 patients matched to Group A for sex, age, neurological status and prophylactic treatment during the acute stage, with no history of DVT. Statistical analysis was performed using the Mann-Whitney and Fisher's exact tests.

RESULTS

Of the individuals in Group A, 14% had no risk factor and 86% had at least one; however, in Group B 54% had no endogenous risk factors and 46% had at least one. None of the individuals in either group had a deficit in their coagulation inhibitors (ATIII, PC and PS), and the LpA level was equivalent in the two groups. The levels of Hcy and PAI-1 were significantly higher in Group A.

CONCLUSIONS

Increases in the levels of plasma Hcy and PAI-1 are demonstrated to be independent risk factors for developing a DVT.

Can haematological tests predict cardiovascular risk? The 2005 Kettle Lecture*

The risk of venous or arterial thrombosis is routinely assessed by clinical variables (risk factors) supplemented by measurement of blood lipids and glucose for arterial thrombotic events. Haematological tests that might play a role in risk prediction include haemostatic variables, haematocrit and inflammatory markers (erythrocyte sedimentation rate, plasma viscosity, white cell count). Recent epidemiological studies of these phenotypes and related genotypes are reviewed. For the risk prediction of first venous thrombosis, screening for thrombophilias in 'high-risk' situations does not appear clinically effective or cost-effective; with the possible exception of women considering oral hormone replacement therapy. General screening after a first venous event to predict recurrence (or risk in asymptomatic relatives) does not appear effective; with the possible exception of d-dimer, which requires further study. For risk prediction of first arterial thrombosis, screening adds little to prediction by current clinical risk scores. Screening of persons after a first arterial event, or with atrial fibrillation (e.g. with D-dimer for stroke prediction), requires further study. In conclusion, haematological tests have very limited roles in the prediction of cardiovascular risk, and should only be used according to evidence-based guidelines. The need for management studies is highlighted.

De novo synthesis of diacylglycerol in endothelium may mediate the association between PAI-1 and the insulin resistance syndrome

Increased free fatty acid flux, giving rise to increased de novo synthesis of diacylglycerol (DAG) and activation of protein kinase C (PKC) in vascular endothelium, may be largely responsible for the endotheliopathy and increased vascular risk associated with insulin resistance syndrome. This mechanism may also mediate, in large part, the increase in plasminogen activator inhibitor-1 (PAI-1) observed in this syndrome. PKC activation promotes transcription of PAI-1 in endothelial cells and other tissues, apparently by boosting the activity of Sp1 transcription factors that bind to the PAI-1 promoter. Plasma PAI-1 correlates inversely with the ability of insulin infusion to suppress free fatty acid levels. Moreover, infusion of triglycerides with heparin - inducing a marked increase in free fatty acids - has been shown to induce a rapid increase in plasma PAI-1. Alternatively, hyperinsulinemia and hypertriglyceridemia have been suggested as mediators of PAI-1 excess in insulin resistance, inasmuch as insulin and VLDL can stimulate PAI-1 production in cell cultures. However, plasma PAI-1 tends to decline in response to hyperinsulinemic clamps and insulin treatment of type 2 diabetes, and gemfibrozil treatment of hypertriglyceridemia does not decrease PAI-1 - suggesting that elevations of insulin or triglycerides are not likely to mediate PAI-1 excess in vivo. Hypertrophied adipose mass can secrete PAI-1, and is likely to contribute to the plasma PAI-1 pool in obese insulin-resistant subjects, but current evidence suggests that this is not likely to be the primary source of the elevated plasma PAI-1 in insulin resistance syndrome. Plasma PAI-1 can be decreased in insulin resistant subjects by improving adipocyte insulin sensitivity (with weight loss and thiazolidinediones), by consuming a very-low-fat diet that minimizes postprandial free fatty acid flux, and by administering activators of AMP-activated kinase (e.g., metformin), which can be expected to lessen tissue DAG synthesis.

Hormone replacement therapy and cardiovascular disease: increased risks of venous thromboembolism and stroke, and no protection from coronary heart disease

Hormone replacement therapy (HRT) was increasingly promoted over the last 40 years to improve quality of life, and to reduce the risks of osteoporotic fractures and coronary heart disease (CHD). In recent years, observational studies, randomized trials and systematic reviews of such trials have shown that HRT does not reduce, but actually increases cardiovascular risk. HRT increases the relative risks of venous thromboembolism (twofold), and of fatal or disabling stroke (by 50%); whilst increasing the early risk of myocardial infarction and having no protective effect against CHD on longer term use. Possible mechanisms for these increased cardiovascular risks include down-regulation of several inhibitory pathways of blood coagulation, resulting in increased coagulation activation, which promotes venous and arterial thrombosis. The implications for prescription are discussed, as are lessons for future evaluation of health care interventions.

Reduced plasma fibrinolytic potential is a risk factor for venous thrombosis

The role of the fibrinolytic system in the development of deep vein thrombosis (DVT) is unclear. We determined the plasma fibrinolytic potential of patients enrolled in the Leiden Thrombophilia Study (LETS), a population-based case-control study on risk factors for DVT. Plasma fibrinolytic potential was determined in 421 patients and 469 control subjects by means of a tissue factor-induced and tissue-type plasminogen activator (tPA)-induced clot lysis assay. Using clot lysis times above the 70th, 80th, 90th, 95th, and 99th percentiles of the values found in control subjects as cut-off levels, we found a dose-dependent increase in risk for DVT in patients with hypofibrinolysis (odds ratios of 1.4, 1.6, 1.9, 2.1, and 2.2, respectively). This indicates a 2-fold increased risk of DVT in subjects with clot lysis times above the 90th percentile. The risk increase was not affected by age or sex (adjusted odds ratio for 90th percentile, 2.0), and after correction for all possible confounders (age, sex, and levels of procoagulant proteins shown to associate with clot lysis times in the control population), the risk estimate was marginally reduced (odds ratio, 1.6 for 90th percentile). Taken together, these results indicate that plasma hypofibrinolysis constitutes a risk factor for venous thrombosis, with a doubling of the risk at clot lysis times that are present in 10% of the population.

The PAI-1 gene 4G/5G polymorphism and deep vein thrombosis in patients with inherited thrombophilia

Genetic and acquired factors may influence phenotypic expression of inherited thrombophilia. Hypofibrinolysis due to excess PAI-1 can be found in patients with deep vein thrombosis (DVT) and 4G/5G polymorphism of the PAI-1 gene may modulate the inhibitor's synthesis. In 149 patients with inherited thrombophilia, the possible thrombotic contribution of both 4G/5G polymorphism and PAI-1 plasma levels was evaluated. Sixty-seven patients with idiopathic DVT and 98 normal subjects were also studied. By comparison with controls, a significantly higher prevalence of 4G/4G genotype was seen in idiopathic DVT and in thrombophilia patients, although in this latter group the difference only remained significant in cases symptomatic for thrombosis (p = 0.01). The 4G/4G genotype was associated with a greater risk of thrombosis both in symptomatic thrombophilia patients (OR 2.85, 95% CI 1.26-6.46) and in idiopathic DVT patients (OR 3.1, 95% CI 1.26-7.59). The greater frequency of 4G allele in symptomatic thrombophilia patients with respect to controls was statistically significant (p = 0.04). Compared to healthy subjects, PAI-1:Ag levels were higher in symptomatic thrombophilia patients and related to the 4G/5G polymorphism, with significantly higher values in the 4G/4G carriers. In conclusion, PAI-1 4G/5G polymorphism may influence PAI-1 expression and thrombotic risk in patients with inherited thrombophilia.

Thrombin-activatable fibrinolysis inhibitor and the risk for recurrent venous thromboembolism

The impact of fibrinolysis for predicting the risk for recurrent venous thromboembolism (VTE) is low. We prospectively followed up 600 patients with a first VTE and evaluated the thrombin-activatable fibrinolysis inhibitor (TAFI) as a risk factor for recurrence. A high TAFI level (75th or higher percentile in thrombosis patients) was associated with a 2-fold higher risk for recurrence compared with lower levels. The probability of recurrence 2 years after anticoagulation was 14.5% (95% confidence interval [CI], 8.6-20.4) among patients with high TAFI levels and 6.8% (95% CI, 4.3-9.3) among patients with lower levels (P = .006). Our data also support the concept of a linkage between fibrinolysis and the coagulation system. Patients with high TAFI levels had significantly higher levels of factors XI, VIII, and IX, and a high risk of recurrence was seen among patients with high TAFI levels and high levels of one of these factors. The relative risk (RR) for recurrence was highest among patients with high TAFI and high factor XI (RR, 2.9; 95% CI, 1.3-6.9), high factor VIII (RR, 6.5; 95% CI, 2.9-14.8), or high factor IX (RR, 2.0; 95% CI, 1.0-3.9) levels compared with patients with low levels of TAFI and one of these factors.

Fibrinolytic activity in multiple myeloma

The incidence of thromboembolic events is high as a result of disease, disease-related complications, and therapy in multiple myeloma (MM). In patients with hematologic tumors, impaired fibrinolysis may be present and may contribute to the development of thrombotic complications. Therefore, we designed a study to investigate fibrinolytic activity in MM. We compared plasma levels of interleukin (IL)-6, C-reactive protein (CRP), IL-1beta, IL-11, tissue plasminogen activator (tPA) activity, plasminogen activator inhibitor-1 (PAI-1) activity, and global fibrinolytic capacity (GFC) in patients with MM (n = 66) and in control subjects (n = 18). The prevalence of venous thromboembolism was 4.5%, with a median follow-up period of 7 months in our myeloma group. Results are given as mean (median, range). Plasma levels of IL-6 (8.27 +/- 0.74 [9.65, 0.90-13.32] pg/mL versus 2.64 +/- 0.66 [1.80, 0.10-11.86] pg/mL, P < 0.001), CRP (45.57 +/- 9.92 [21.00, 1.34-330.00] mg/L versus 1.96 +/- 0.50 [1.05, 0.19-8.03] mg/L, P < 0.001), PAI-1 (7.40 +/- 0.67 [5.57, 2.40-31.80] IU/mL versus 4.73 +/- 0.65 [3.60, 2.32-11.00] IU/mL, P < 0.01), GFC score (1.90 +/- 0.02 [2, 1-3] versus 2.50 +/- 0.14 [3, 1-3], P < 0.001) were increased compared with controls. In patients with MM, the level of IL-6 was positively correlated with CRP (r = 0.66, P < 0.001), IL-1beta (r = 0.29, P < 0.05), and PAI-1 (r = 0.35, P < 0.01) and negatively correlated with GFC (r = -0.37, P < 0.01). CRP level was positively correlated with plasma PAI-1 level (r = 0.40, P < 0.01) and negatively correlated with GFC (r = -0.44, P < 0.001). A significant negative correlation between PAI-1 level and GFC (r = -0.75, P < 0.001) was also detected. IL-1beta levels were negatively correlated with tPA level (r = -0.26, P < 0.05). These results suggest that patients with myeloma have a decreased fibrinolytic activity mainly because of increased PAI-1 activity. In MM, increased PAI-1 activity seems to be related with elevated IL-6 level. MM should be considered as a hypercoagulable state as a result of both increased procoagulant activity and decreased fibrinolytic activity. Achieving a plateau by means of conventional chemotherapies does not improve the decreased fibrinolytic activity.

Comparison of six D-dimer methods in patients suspected of deep vein thrombosis

We evaluated six D-dimer methods to determine their sensitivity, specificity, and negative predictive values (NPV) in symptomatic patients suspected of deep vein thrombosis (DVT). In patients suspected of DVT a whole blood D-dimer test (SimpliRED, Agen) was performed, and then tested using enzyme-linked immunosorbent assay (VIDAS D-Dimer, BioMerieux; Asserachrome D-Di, Stago International; Dimertest Gold, Agen) and automated immunoturbidometric methods (Advanced D-Dimer, Dade Behring; MiniQuant, Biopool). Each D-dimer method was independently compared with radiographic results to determine sensitivity and NPV. There were 151 patients enrolled in the study. Thirty-five (23.2%) patients had a positive Doppler ultrasound, with 26 proximal, eight distal, and one patient with both proximal and distal thrombus. Two patients (1.3%) had inconclusive studies and were excluded from the analyses. For all patients, the sensitivities for the rapid D-dimer methods were: SimpliRED, 82.3% [95% confidence interval (CI), 80.3-84.3%]; VIDAS D-Dimer, 91.4% (95% CI, 89.9-92.9%); MiniQuant D-Dimer, 96.3% (95% CI, 95.1-97.5%); and Advanced D-Dimer, 97.1% (95% CI, 96.3-97.9%). The sensitivity improved for SimpliRED (86.4%; 95% CI, 83.3-89.4%), VIDAS D-Dimer (95.5%; 95% CI, 85.0-100%), MiniQuant D-Dimer (100%; 95% CI, 96.9-100%) and Advanced D-Dimer (100%; 95% CI, 98.9-100%) in the inpatient population. The automated immunoturbidometric methods, the MiniQuant D-Dimer and Advanced D-Dimer, demonstrated comparable sensitivities and NPV with the VIDAS D-Dimer method in symptomatic patients suspected of DVT, which would suggest that these newer D-dimer methods could be used as part of the diagnostic algorithm for patients suspected of DVT.

Incidence of recurrent venous thromboembolism in relation to clinical and thrombophilic risk factors: prospective cohort study

BACKGROUND

Stratification for risk of recurrence after a first episode of venous thromboembolism (VTE) would affect the duration of anticoagulant therapy. We aimed to determine the incidence of recurrence of VTE in relation to clinical risk factors and standard laboratory testing for heritable thrombophilic defects.

METHODS

We established a database to prospectively follow-up a cohort of unselected patients who had had a first episode of objectively proven VTE. We excluded patients with malignant disease and antiphospholipid syndrome. All patients were offered testing for heritable thrombophilia.

FINDINGS

At 2 years, the cumulative recurrence rate in 570 patients was 11%. Incidence was lowest after surgery-related VTE (0%) and highest after unprecipitated VTE (19.4%) (p<0.001). 85% of patients were tested for heritable thrombophilic defects. Recurrence rates were not related to presence or absence of laboratory evidence of heritable thrombophilia (hazard ratio 1.50 [95% CI 0.82-2.77]; p=0.187). In patients with a first event that was unprecipitated or was associated with a non-surgical trigger, recurrence rates did not differ in patients with or without thrombophilia (1.34 [0.73-2.46]; p=0.351).

INTERPRETATION

In unselected patients who have had a first episode of VTE, testing for heritable thrombophilia does not allow prediction of recurrent VTE in the first 2 years after anticoagulant therapy is stopped. However, assessment of clinical risk factors associated with the first episode of VTE does predict risk of recurrence. Patients with postoperative VTE have a very low rate of recurrence.

Relationship of metabolic syndrome and fibrinolytic dysfunction to cardiovascular disease

BACKGROUND

The clustering of impaired glucose metabolism, elevated triglycerides, low HDL cholesterol, and abdominal obesity is known as the metabolic syndrome. Individuals with this syndrome suffer an excess of cardiovascular disease (CVD) for reasons that are unclear.

METHODS AND RESULTS

We randomly sampled 1276 adults of South Asian, Chinese, European, and Native Indian ancestry from 4 communities in Canada. Participants provided fasting blood samples for glucose, lipids, and fibrinolytic measurements; had an oral glucose tolerance test; and underwent a B-mode carotid ultrasound examination. CVD was determined by history and ECG. The prevalence of the metabolic syndrome was 25.8% (95% CI, 23.5 to 28.2) and varied substantially by ethnic group: 41.6% among Native Indians, 25.9% among South Asians, and 22.0% among Europeans, compared with 11.0% among the Chinese (overall, P=0.0001). People with the metabolic syndrome had more atherosclerosis (maximum intimal medial thickness, 0.78+/-0.18 versus 0.74+/-0.18 mm; P=0.0005), CVD (17.2% versus 7.0%; P=0.0001), and elevated plasminogen activator inhibitor-1 (24.2 versus 14.6 U/mL; P=0.001) compared with levels among people without the metabolic syndrome. For the same amount of atherosclerosis, people with the metabolic syndrome had a greater prevalence of CVD, even among nondiabetic individuals. This difference in CVD prevalence among the groups was attenuated after adjustment for plasminogen activator inhibitor-1 levels, suggesting that fibrinolytic dysfunction mediates the increased risk of CVD in individuals with the metabolic syndrome.

CONCLUSIONS

CVD among people with the metabolic syndrome is explained by their excess of atherosclerosis and impaired fibrinolysis. Interventions to prevent atherosclerosis progression and improve fibrinolytic function require evaluation in this high-risk group.

Prospective study of fibrinolytic markers and venous thromboembolism

Prior research has conflicted on whether increased levels of plasma fibrinolytic factors may identify patients at risk of venous thromboembolism (VTE). We therefore performed a nested case-control study of VTE within two prospective population-based studies. In 308 participants who developed VTE and 640 controls, we measured PAI-1 antigen, tPA/PAI-1 complex, plasmin-alpha 2-antiplasmin (PAP), and the PAI-1 -675 4G/5G promoter polymorphism on pre-event blood samples. There was no overall association between any of these fibrinolytic variables and VTE, after adjustment for age or for multiple VTE risk factors. There was weak evidence for an interaction of PAP with elevated factor VIIIc and elevated D-dimer in augmenting VTE risk. We conclude that, for the most part, these fibrinolytic markers do not identify healthy subjects at risk for VTE.

Fibrin fragment D-dimer and the risk of future venous thrombosis

Plasma D-dimer concentration rises more than 100-fold during acute deep vein thrombosis, but there are no prospective data concerning D-dimer as a risk factor for incident venous thrombosis in a general population. Incident venous thrombosis was ascertained in 2 prospective observational studies, the Atherosclerosis Risk in Communities Study and the Cardiovascular Health Study. Of 21 690 participants enrolled between 1987 and 1993, after 8 years of follow-up, D-dimer was measured using baseline stored plasma of 307 participants who developed venous thrombosis and 616 who did not. Relative to the first quintile of the distribution of D-dimer, the age-adjusted odds ratios for future venous thrombosis for the second to fifth quintiles of D-dimer were 1.6, 2.3, 2.3, and 4.2, respectively (P for trend <.0001). Following added adjustment for sex, race, body mass index, factor V Leiden, prothrombin 20210A, and elevated factor VIII coagulant activity (factor VIII:c), these odds ratios were 1.5, 2.1, 1.9, and 3.0, respectively (P for trend <.0001). Among those with idiopathic thrombosis or secondary thrombosis unrelated to cancer, the adjusted fifth quintile odds ratios were 3.5 and 4.8, respectively. By contrast, D-dimer in the fifth versus first quintile was not related to occurrence of cancer-associated thrombosis (odds ratio, 1.1). Odds ratios for elevated D-dimer were consistently elevated in subgroups defined by age, sex, race, duration of follow-up, and thrombosis type (deep vein thrombosis or pulmonary embolus). D-dimer is strongly and positively related to the occurrence of future venous thrombosis.

Plasminogen and tissue-type plasminogen activator deficiency as risk factors for thromboembolic disease

OBJECTIVE

To review the published evidence for an association between a deficiency of plasminogen or tissue-type plasminogen activator (tPA) and the risk of thrombosis.

DATA SOURCES

Review of the medical literature, with an emphasis on the last 10 years.

DATA EXTRACTION AND SYNTHESIS

After an initial assessment of the literature, including review of clinical study design and laboratory methods, a draft manuscript summarizing the findings was prepared and circulated to participants in the College of American Pathologists Conference on Diagnostic Issues in Thrombophilia. The key findings and each recommendation were presented for discussion at the conference. Recommendations were accepted if a consensus of the 27 experts attending the conference was reached. The results of the discussion were used to revise the manuscript into its final form.

CONCLUSIONS

The consensus of the conference was that routine laboratory assessment of plasminogen and tPA concentration in patients with thrombophilia is not warranted at this time. Analysis of plasminogen and tPA gene alterations in patients with thrombophilia is also not warranted at this time. Determination of plasminogen concentration should be performed in patients suspected of having ligneous conjunctivitis.

Plasminogen activator inhibitor-1 levels and polymorphisms

OBJECTIVE

To review the published evidence of a relationship between levels of plasminogen activator inhibitor-1 (PAI-1) or the 4G/5G polymorphism of the PAI-1 gene and the occurrence of venous thromboembolic disease.

METHODS

Review of the medical literature using computerized databases and a review of secondary sources identified through bibliographies.

DATA SYNTHESIS

Plasminogen activator inhibitor-1 is an important inhibitor of the fibrinolytic system, so it is biologically plausible that elevated levels could suppress fibrinolysis and result in an increased risk of thrombosis. Several small studies reported associations between PAI-1 levels and venous thromboembolism, some of which appear to be familial. Problems with these studies include variations in PAI-1 plasma levels due to circadian changes and the acute phase response, as well as alterations due to common comorbid disease states. More recent investigations have focused on genetic polymorphisms, particularly the 4G/5G insertion/deletion in the promoter region, affecting transcription rates. The relation of 4G/5G to venous thrombosis has been investigated primarily in case-control studies, which have produced inconsistent findings. Most studies, however, have reported higher PAI-1 plasma levels in individuals with 4G/4G.

CONCLUSIONS

The evidence regarding the relationship between an elevated PAI-1 plasma level or PAI-1 genetic polymorphism and the risk of venous thromboembolism is conflicting. There is insufficient information to recommend use of PAI-1 levels or genotype in evaluating thrombophilia.

Update on selected inherited venous thrombotic disorders

The inherited thrombophilias are a group of inherited conditions that predispose to thrombotic events. Most of the inherited thrombotic disorders are associated with venous thromboembolism rather than arterial thrombosis. Frequently, one or more predisposing genetic factors and/or environmental risk factor are identified in thrombosis patients. Significant advances in the identification of etiologies of inherited thrombosis have recently been reported. The most common inherited thrombotic disorders include activated protein C (APC) resistance (factor V Leiden), hyperhomocysteinemia, the prothrombin gene variant G20210A, elevated factor VIII levels, and deficiencies of thrombomodulin, protein C, protein S, and antithrombin. Less well characterized disorders include elevated factor IX, X, and XI levels. Recognition of these disorders now permits a laboratory diagnosis in approximately 70% of patients being evaluated for inherited thrombosis. This review focuses on the clinical and laboratory aspects of some of the most common inherited venous thrombotic disorders, including APC resistance, hyperhomocysteinemia, the prothrombin G20210A mutation, and elevated coagulation factor levels.