An immunoassay for human D dimer using monoclonal antibodies

Advances in D-dimer testing: progress in harmonization of clinical assays and innovative detection methods

The D-dimer is a sensitive indicator of coagulation and fibrinolysis activation, especially valuable as a biomarker of intravascular thrombosis. Measurement of plasma D-dimer levels plays a crucial role in the diagnosis and monitoring of conditions such as deep vein thrombosis, pulmonary embolism, and disseminated intravascular coagulation. A variety of immunoassays, including enzyme-linked immunosorbent assays, latex-enhanced immunoturbidimetric assays, whole-blood aggregation analysis, and immunochromatography assays, are widely used in clinical settings to determine D-dimer levels. However, the results obtained from different D-dimer assays vary significantly. These assays exhibit intra-method coefficients of variation ranging from 6.4% to 17.7%, and the measurement discrepancies among different assays can be as high as 20-fold. The accuracy and reliability of D-dimer testing cannot be guaranteed due to the lack of an internationally endorsed reference measurement system (including reference materials and reference measurement procedures), which may lead to misdiagnosis and underdiagnosis, limiting its full clinical application. In this review, we present an in-depth analysis of clinical D-dimer testing, summarizing the existing challenges, the current state of metrology, and progress towards harmonization. We also review the latest advancements in D-dimer detection techniques, which include mass spectrometry and electrochemical and optical immunoassays. By comparing the basic principles, the definition of the measurand, and analytical performance of these methods, we provide an outlook on the potential improvements in D-dimer clinical testing.

Hemostasis from Bench to Bedside: The History of Three Successful Stories of Translational Medicine

Looking at the history of hemostasis, one can easily conclude that most of the achievements we see today have been done through the ingenuity and dedication of scientists, who devoted their efforts to translate the basic concepts behind their hypotheses from the laboratory to the patient bedside. I am personally excited by three of these stories. This article aims to review the history on the development of D-dimer, heparin, and coagulometers, which have been chosen as paradigmatic examples of diagnostic testing, drugs, and measuring devices, respectively. They should be considered among the most successful histories of translational medicine.

Engineered Molecular Therapeutics Targeting Fibrin and the Coagulation System: a Biophysical Perspective

The coagulation cascade represents a sophisticated and highly choreographed series of molecular events taking place in the blood with important clinical implications. One key player in coagulation is fibrinogen, a highly abundant soluble blood protein that is processed by thrombin proteases at wound sites, triggering self-assembly of an insoluble protein hydrogel known as a fibrin clot. By forming the key protein component of blood clots, fibrin acts as a structural biomaterial with biophysical properties well suited to its role inhibiting fluid flow and maintaining hemostasis. Based on its clinical importance, fibrin is being investigated as a potentially valuable molecular target in the development of coagulation therapies. In this topical review, we summarize our current understanding of the coagulation cascade from a molecular, structural and biophysical perspective. We highlight single-molecule studies on proteins involved in blood coagulation and report on the current state of the art in directed evolution and molecular engineering of fibrin-targeted proteins and polymers for modulating coagulation. This biophysical overview will help acclimatize newcomers to the field and catalyze interdisciplinary work in biomolecular engineering toward the development of new therapies targeting fibrin and the coagulation system.

Is it possible to make a common reference standard for D-dimer measurements? Communication from the ISTH SSC Subcommittee on Fibrinolysis

BACKGROUND

D-dimer antigen is a heterogeneous mixture of fibrin degradation products that when present at high levels in plasma indicate ongoing coagulation and fibrinolysis. The heterogeneous nature of the target D-dimer antigen and the variety of assay systems means that it is difficult to compare results from different methods.

OBJECTIVES

To identify a universally agreed D-dimer standard that could help harmonize results from different methods.

METHODS

A pool of patient plasma with high D-dimer levels was freeze-dried and investigated as a long-term World Health Organization international standard for D-dimer. Fibrin degradation products from clot lysis reactions were also freeze-dried in various formulations and investigated in commutability studies with patient plasma.

RESULTS

Problems of instability of D-dimer plasma emerged suggesting loss of reactivity after freeze-drying and storage at -20°C of 10%-18% per year. Freeze-dried fibrin degradation products added to plasma were also unstable, but the sugar trehalose was found to improve stability. However, this preparation was not suitable as a standard in widely used assay platforms. Previous studies suggest fibrin degradation products are prone to structural rearrangements and amyloid formation, which may explain the instability of candidate D-dimer standards.

CONCLUSIONS

The known difficulties of D-dimer standardization are compounded by instability of D-dimer antigen after freeze-drying, described in this report. Fibrin degradation products added to plasma and stabilized by trehalose are not suitable as a standard for D-dimer measurement harmonization. Trehalose stabilization of pooled patient plasma containing high D-dimer levels may produce a useful standard, but this requires confirmation.

Diagnostic value of D-dimers for limb deep vein thrombosis in children: A prospective study

The present study sought to evaluate the discriminative and predictive ability of D-dimer for pediatric limb DVT. Children aged 28 days-18 years requiring imaging to rule out limb DVT, as per the treating clinical team, were enrolled in the study. The outcome was ultrasound proven DVT. The D-dimer levels were obtained around the time of imaging. Receiver operating characteristic (ROC) curves and logistic regression models were used for data analyses. In total, 296 patients were enrolled between 2017-2020; 204 patients were diagnosed with DVT (DVT[+]). Median D-dimer levels were 2.3 μg/ml FEU (25th-75th percentile 0.9-3.9) among DVT(+) and 1.9 μg/ml FEU (25th-75th percentile 0.8-4.0) among DVT(-) patients (p = 0.60). The area under the ROC curve (AUC) was 0.52 (95% confidence interval [CI] 0.45-0.59). The odds ratio for D-dimer levels was 1.00 (95% CI 0.99-1.01), holding confounders constant. In a sub-group exploratory analysis including 23 patients with no underlying conditions or co-morbidities, the AUC curve was 0.90 (95% CI 0.76-1.00). In conclusion, in this prospective cohort study of consecutive children with suspected limb DVT, D-dimer levels had poor discriminative and predictive ability for DVT. However, D-dimer levels showed better discriminative and predictive ability for DVT in an exploratory sample of patients with no underlying conditions or co-morbidities at the time of diagnosis.

Non-Compartment and compartmental pharmacokinetics, efficacy, and safety of Kedrion FIX concentrate

BACKGROUND

An open-label phase II, multicenter clinical trial was conducted at 11  Haemophilia Centres in  Italy, Romania, and Turkey, to evaluate the pharmacokinetics (PK), efficacy, and safety of high purity, plasma-derived, double virus inactivated and double nano-filtered factor IX (pd-FIX) concentrate (Kedrion FIX), EudraCT Number: 2005-006186-14.

MATERIAL AND METHODS

16 previously treated patients (PTPs) with severe or moderately severe haemophilia B were enrolled in the study. At enrolment, 14 underwent the first PK assessment (PK I), and the second PK (PK II) assessment was performed after six months of treatment (5 on-demand and nine prophylaxis) at the end of the study. PK parameters were evaluated by Non-Compartmental Analysis (NCA), One-Compartment model (OCM), and Two-Compartment Model (TCM). Efficacy of Kedrion FIX in all 16 patients was evaluated by the number of bleeding events, and clinical response following the infusions. Periodic FIX inhibitor assays and thrombogenicity tests were scheduled throughout the study to assess the safety of the drug.

RESULTS

As compared to the published data on PK of pdFIX, Kedrion FIX displayed a longer half-life (22.37-55.73 hrs), reduced clearance, and regular volume of distribution at PK I by both NCA and OCM. The comparison of outcomes of PK II with those of PK I by OCM,  also showed significant changes, particularly in patients on prophylaxis, who showed some improved parameters of PK. Due to two outlier values at the end of the trial, the NCA parameters of PK I were not compared to those of PK II. Breakthrough bleeds were successfully treated with 1 or 2 infusions. No significant adverse events were observed during the study.

DISCUSSION

During the six-month clinical study period, the use of Kedrion FIX resulted in a safe and effective pd-FIX concentrate with excellent PK characteristics.

DNA-bound elastase of neutrophil extracellular traps degrades plasminogen, reduces plasmin formation, and decreases fibrinolysis: proof of concept in septic shock plasma

Activation of platelets and neutrophils in septic shock results in the formation of microvascular clots containing an intricate scaffold of fibrin with neutrophil extracellular traps (NETs) DNA. NETs contain multiple components that might impact endogenous fibrinolysis, resulting in failure to lyse clots in the microcirculation and residual systemic microthrombosis. We propose herein that the reservoir of human neutrophil elastase (HNE) on NETs may directly interfere with the fibrinolytic mechanism via a plasminogen proteolytic pathway. To investigate this mechanism, we constructed fibrin-NETs matrices by seeding and activating neutrophils onto a fibrin surface and monitored plasminogen activation or degradation. We demonstrate that the elastase activity of HNE-DNA complexes is protected from inhibition by plasma antiproteases and sustains its ability to degrade plasminogen. Using mass spectrometry proteomic analysis, we identified plasminogen fragments composed of kringle (K) domains (K₁₊₂₊₃, k_1+2+3+4) and the serine protease (SP) region (K₅-SP). We further demonstrate that patients with septic shock with disseminated intravascular coagulation have circulating HNE-DNA complexes, HNE-derived plasminogen fragments, a low plasminogen concentration, and a reduced capacity to generate plasmin onto fibrin. In conclusion, we show that NETs bearing active HNE-DNA complexes reduce plasminogen into fragments, thus impairing fibrinolysis by decreasing the local plasminogen concentration, plasminogen binding to fibrin, and localized plasmin formation.-Barbosa da Cruz, D., Helms, J., Aquino, L. R., Stiel, L., Cougourdan, L., Broussard, C., Chafey, P., Riès-Kautt, M., Meziani, F., Toti, F., Gaussem, P., Anglés-Cano, E. DNA-bound elastase of neutrophil extracellular traps degrades plasminogen, reduces plasmin formation, and decreases fibrinolysis: proof of concept in septic shock plasma.

Biosensing of D-dimer, making the transition from the central hospital laboratory to bedside determination

Since the disclosure of the fibrinogen degradation mechanism, around half a century ago, a significant number of papers have been published related to the clinical relevance of D-dimer, a molecule immune to additional enzymatic decomposition by plasmin. Due to the obliquity of regulating blood coagulation in pathological events, the number of diseases and conditions associated with abnormal levels of D-dimer includes deep vein thrombosis, pulmonary embolism, sepsis, myocardial infarction, disseminated intravascular coagulation, among many others. D-dimer not only is an important player in medical diagnosis but also its role as a prognosis biomarker is being revealed. However, the number of analytical alternative methods has not accompanied this trend, even though novel simple point-of-care devices would certainly boost the relevance of D-dimer in emergency medicine. Some reasons for that could be related to the fact that D-dimer is a challenging analyte present in complex samples like blood. In this manuscript, subsequent to a fibrinogen degradation process introduction, it is provided a historical overview of the early D-dimer assays, followed by an extended focus on innovative solutions, with a spotlight on the electrochemical bioanalytical devices. The discussion is accompanied with a critical analysis and concluding thoughts concerning future perspectives.

D-dimer: Preanalytical, analytical, postanalytical variables, and clinical applications

D-dimer is a soluble fibrin degradation product deriving from the plasmin-mediated degradation of cross-linked fibrin. D-dimer can hence be considered a biomarker of activation of coagulation and fibrinolysis, and it is routinely used for ruling out venous thromboembolism (VTE). D-dimer is increasingly used to assess the risk of VTE recurrence and to help define the optimal duration of anticoagulation treatment in patients with VTE, for diagnosing disseminated intravascular coagulation, and for screening medical patients at increased risk of VTE. This review is aimed at (1) revising the definition of D-dimer; (2) discussing preanalytical variables affecting the measurement of D-dimer; (3) reviewing and comparing assay performance and some postanalytical variables (e.g. different units and age-adjusted cutoffs); and (4) discussing the use of D-dimer measurement across different clinical settings.

Generation and characterization of D-dimer specific monoclonal antibodies for use in latex agglutination test

The commercially available D-dimer assays used in the clinical practice often show differences in the results, and their specificity and sensitivity are rather unsatisfactory. Our aim was to develop a new monoclonal antibody against D-dimer with a proper specificity, and estimating its suitability using in a latex agglutination diagnostic test. Monoclonal antibodies were generated using hybridoma technology. Their titer was determined by a self-developed ELISA method. The cross-reactions of the antibodies were tested. Characterization of the epitope specificity of a selected antibody was performed through digestion of D-dimer followed by Western blotting. The amino acid sequences of the active antigen fragments were determined. According to the ELISA results, 38 cell groups were constated as antibody-producing hybridomas, among them 7 gave raised titer of antibody and were cloned. Based on the cross-reaction analysis, none of the antibodies gave cross-reaction with fibrin-E and fibrinogen-E fragments but reacted with fibrin D and fibrinogen D fragments. A low cross-reaction was showed with fibrinogen and fibrin X and Y. Contrary to the others, antibody 2B9 gave no cross-reaction with fibrinogen and reacted weakly with fibrin X and Y fragments. According to the epitope analysis the antibody 2B9 binds to amino acids 94-99 and to amino acids 140-147 on the beta chain and it recognizes the amino acids 23-32 and 93-98 on the gamma chain of D-dimer. Considering the characteristics of the above mentioned monoclonal antibody 2B9, we found that it is suitable to be a basis for a D-dimer diagnostic test with proper specificity.

D-Dimer Testing: Laboratory Aspects and Current Issues

D-dimer has become one of the commonly requested coagulation tests, especially in the venous thromboembolism rule out setting. Appropriate D-dimer testing has significantly decreased the number of radiological investigations in this clinical scenario. D-dimer testing also plays an important role in the diagnostic process of the systemic coagulation disorders, especially disseminated intravascular coagulation in conjunction with other coagulation tests. However, widespread D-dimer testing without good understanding of the technical issues related to the test has recently caused some concerns. This review aims to address the basic physiology of D-dimer formation, the different methods available for its routine assessment, the current problems that both clinicians and laboratory scientists face with this test, and the important need for harmonization of commercial immunoassays.

How to use D-dimer in acute cardiovascular care

D-dimer testing is important to aid in the exclusion of venous thromboembolic events (VTEs), including deep venous thrombosis and pulmonary embolism, and it may be used to evaluate suspected aortic dissection. D-dimer is produced upon activation of the coagulation system with the generation and subsequent degradation of cross-linked fibrin by plasmin. Many different assays for D-dimer testing are currently used in routine care. However, these tests are neither standardized nor harmonized. Consequently, only clinically validated assays and assay specific decision limits should be used for routine testing. For the exclusion of pulmonary embolism/deep vein thrombosis, age-adjusted cut-offs are recommend. Clinicians must be aware of the validated use of their hospital's D-dimer assay to avoid inappropriate use of this biomarker in routine care.

Increased Soluble Fibrin in Plasma of Patients with Disseminated Intravascular Coagulation

Plasma levels of soluble fibrin (SF) were measured in 1184 patients with disseminated intravascular coagulation (DIC) according to Japanese Ministry of Health and Welfare (JMHW) criteria. The usefulness of SF for the diagnosis of DIC was compared with other hemostatic molecular markers. Most hemostatic markers were significantly increased in patients with DIC than in those without DIC. Plasma levels of fibrin and fibrinogen degradation products, thrombin-antihtrombin complex, plasmin-plasmin inhibitor complex, D-dimer, thrombomodulin, and SF levels were also significantly higher in those with pre-DIC than in those without DIC. In classification of overt DIC by International Society of Thrombosis and Haemostasis (ISTH) criteria, most hemostatic markers were significantly increased in patients with overt DIC than in those without overt DIC. Plasma levels of SF 'in patients with DIC were significantly higher than those in patients with pre-DIC, which were significantly higher than in those without DIC. Plasma levels of SF were also significantly higher in patients with overt DIC than in those with non-overt DIC. The correlation between plasma SF levels and DIC score according to JMHW criteria or ISTH criteria was good. Receiver operating characteristic analysis shows that SF was the best marker for the diagnosis of DIC or overt DIC. These findings suggest that plasma SF might be useful marker for the diagnosis of DIC or overt DIC.

The evolution of fibrin-specific targeting strategies

Fibrin-specific targeting capabilities have been highly sought for over 50 years due to their implications for bio-molecule delivery, diagnostics, and regenerative medicine. Yet only recently has our full knowledge of fibrin's complex polymerization dynamics and biological interactions begun to be fully exploited in pursuit of this goal. This highlight will discuss the range of rapidly changing strategies for specifically targeting fibrin over the precursor fibrinogen and the advantages and disadvantages of these approaches for various applications.

Accuracy and safety of (99m)Tc-labeled anti-D-dimer (DI-80B3) Fab' fragments (ThromboView®) in the diagnosis of deep vein thrombosis: a phase II study

BACKGROUND

The assessment of patients with suspected deep vein thrombosis (DVT) remains challenging despite current diagnostic algorithms. (99m)Tc-labelled DI-DD3B6/22-80B3 Fab´ fragments ((99m)Tc-DI-80B3, ThromboView®) is a novel diagnostic test that uses a radiolabelled humanized monoclonal antibody fragment specific for the D-dimer region of cross-linked fibrin to detect DVT. This test has an anatomic component to locate DVT and a functional component to differentiate acute (newly formed) thrombus from inactive (old) thrombus.

METHODS

In a multi-centre prospective cohort trial we investigated the diagnostic accuracy and safety of (99m)Tc-DI-80B3 in consecutive patients with suspected DVT who had the diagnosis confirmed or excluded by venography.

RESULTS

We enrolled 94 patients with suspected DVT of whom 12 did not have (99m)Tc-DI-80B3 imaging, leaving 82 patients for the safety analysis. Of these patients, there were 16 with non-evaluable imaging (11 venography, 7 (99m)Tc-DI-80B3, both in two patients) leaving 66 patients for the accuracy analysis. (99m)Tc-DI-80B3 imaging was well-tolerated: 2 patients developed urticaria; none developed serious adverse events. For proximal DVT, the sensitivity (84.2%; 95% confidence interval [CI]: 62.4-94.5) and specificity (97.6%; CI: 83.3-99.4) were highest when the combined 0.25-hour and 3-hour (99m)Tc-DI-80B3 images were used. The accuracy was lower for distal DVT, irrespective of the images used. There were insufficient patients to comment on the accuracy of (99m)Tc-DI-80B3 imaging for suspected recurrent DVT.

CONCLUSIONS

(99m)Tc-DI-80B3 (ThromboView®) is a novel diagnostic modality for patients with suspected DVT with a promising accuracy and safety profile that justifies additional clinical development in diagnostic accuracy and clinical management studies.

D-dimer testing in laboratory practice

BACKGROUND

D-dimer is a reliable and sensitive index of fibrin deposition and stabilization. As such, its presence in plasma should be indicative of thrombus formation. There are many conditions unrelated to thrombosis in which D-dimer concentrations are high, however, making its positive predictive value rather poor.

CONTENT

Notwithstanding these limitations, D-dimer can be regarded as a most valuable laboratory tool to diagnose and manage a vast array of thrombosis-related clinical conditions, including (a) diagnosis of venous thromboembolism (VTE), (b) identification of individuals at increased risk of first thrombotic event (both arterial and venous), (c) identification of individuals at increased risk of recurrent VTE, (d) establishment of the optimal duration of secondary prophylaxis after a first episode of VTE, (e) pregnancy monitoring, and (f) diagnosis/monitoring of disseminated intravascular coagulation (DIC). This article is aimed at reviewing the merits and pitfalls of these applications.

SUMMARY

From my analysis of the literature, I draw the following conclusions. (a) D-dimer, as measured by a sensitive test, can be safely used to exclude VTE in symptomatic outpatients, provided that it is used in combination with the pretest clinical probability. (b) High concentrations of D-dimer are associated with an increased risk of recurrent VTE. (c) Patients who present with D-dimer above cutoff after stopping the regular course of oral anticoagulation benefit from extended prophylaxis. (d) Finally, D-dimer can be used as a fibrin-related degradation marker for the diagnosis/management of patients with DIC.

Detection of pulmonary emboli with 99mTc-labeled anti-D-dimer (DI-80B3)Fab' fragments (ThromboView)

RATIONALE

We report a new method to diagnose acute pulmonary embolism (PE) by single photon emission computerized tomography (SPECT) after administration of (99m)Tc-labeled anti-D-dimer (DI-80B3) monoclonal antibody Fab' fragments. This novel technique provides an additional approach to diagnosing PE in patients for whom other methods are nondiagnostic or contraindicated.

OBJECTIVES

We performed a prospective, multicenter study to investigate the sensitivity and specificity of (99m)Tc-DI-80B3/SPECT in patients with suspected acute PE.

METHODS

Subjects with a moderate to high clinical probability of PE or a positive D-dimer test underwent a PE-protocol contrast-enhanced multidetector thoracic computed tomography (CT) scan as well as (99m)Tc-DI-80B3/SPECT (0.5 mg (99m)Tc-DI-80B3 intravenously followed by a thoracic SPECT 2.5 h later). Separate and independent adjudication committees, blinded to clinical data and other test results, interpreted the (99m)Tc-DI-80B3/SPECT scans (PE detected as foci of abnormally increased (99m)Tc uptake) and the thoracic CT scans using Prospective Investigation of Pulmonary Embolism Diagnosis II criteria.

MEASUREMENTS AND MAIN RESULTS

Of the 52 patients who were enrolled and completed both tests, 42 had both evaluable SPECT scans and thoracic CT scans. Using the criterion standard (thoracic CT scan) there were 21 patients with PE and 21 without. (99m)Tc-DI-80B3/SPECT had a sensitivity of 76.2% (95% confidence interval, 52.8-91.8%) and a specificity of 90.5% (95% confidence interval, 69.8-98.8%). Treatment-related serious adverse events did not occur.

CONCLUSIONS

(99m)Tc-DI-80B3/SPECT was sensitive and specific for acute PE in subjects with moderate to high clinical probability of PE or a positive D-dimer test. (99m)Tc-DI-80B3/SPECT demonstrated an acceptable safety profile and avoids exposure to contrast.

Pulmonary emboli imaging with (99m)Tc-labelled anti-D-dimer (DI-80B3) Fab' followed by SPECT

OBJECTIVES

Pre-clinical experiments demonstrated that intravenous (99m)Tc labelled DI-DD-3B6/22-80B3 humanised anti-fibrin-D-dimer Fab' fragments ((99m)Tc-DI-80B3) allowed scintigraphic imaging of acute pulmonary emboli (PE). The aims of this clinical study were to determine the safety of (99m)Tc-DI-80B3 in patients with PE and evaluate the resulting scintigraphic images for the localisation of acute PE.

MATERIALS/PATIENTS AND METHODS

(99m)Tc-DI-80B3 (0.5mg, 710-850MBq) was administered intravenously to subjects (n=14) with segmental or larger PE on recent contrast-enhanced helical CT scans. Thoracic SPECT scans were acquired 15 minutes, 2 hours and 4 hours afterwards. Subjects were followed for 90 days subsequently.

RESULTS

There were no serious adverse events or antibody responses associated with (99m)Tc-DI-80B3 administration. Focal accumulations of (99m)Tc-DI-80B3 on the SPECT images of the thorax acquired at four hours corresponded to pulmonary emboli detected by CT. Two independent "blinded" SPECT readers identified 79% and 71% (respectively) of the right lung and 79% and 64% (respectively) of the left lung in which CT scans disclosed PE.

CONCLUSIONS

(99m)Tc-DI-80B3 is well-tolerated in patients with acute PE and does not induce an immune response. (99m)Tc-DI-80B3 may offer a novel approach to imaging PE in a clinically acceptable timeframe without exposure to potentially nephrotoxic radiographic contrast agents.

SPECT imaging of pulmonary emboli with radiolabeled thrombus-specific imaging agents

The safe and accurate diagnosis of acute pulmonary embolism (PE) remains challenging, and many PE-related deaths still occur before the detection of PE. Current techniques detect PE as "negative images," ie, the absence of contrast or downstream perfusion. There would be advantages to obtaining "positive images" of PE, by targeting imaging agents to components that are present primarily on thromboemboli. In addition to providing alternative means of diagnosing acute PE, they would also enable acute PE to be distinguished from other types of pulmonary arterial obstruction, such as unresolved intravascular defects attributable to previous PE. Positive images of PE require imaging agents to bind onto target antigens that are present predominantly on thromboemboli. The "D dimer" regions of polymerized fibrin are present in high concentrations on thromboemboli and are sufficiently accessible to binding. (99m)Tc-lableled anti-D-dimer deimmunized monoclonal antibody Fab' fragments (DI-DD-3B6/22-80B3) bind specifically to thromboemboli, with a thrombus: blood labeling ratio that allows scintigraphic detection. Another thrombus-specific imaging agent is (99m)Tc-labeled apcitide, a synthetic peptide that binds with a high affinity and specificity to the glycoprotein IIb/IIIa receptor on the membrane of activated platelets. Both of these agents have enabled the detection of lower extremity deep vein thrombi by planar scintigraphy. However, even highly radiolabeled PEs are difficult to distinguish by planar scintigraphy from the large blood pool in the heart and lungs. The spatial and contrast resolution inherent to single-photon emission computed tomography (SPECT) scanning allow the in situ imaging of pulmonary emboli that have been bound by radiolabeled thrombus-specific imaging agents. Preliminary trials in humans with acute PE have shown that the emboli can be detected after intravenous administration of (99m)Tc-lableled anti-D dimer, followed by SPECT scanning. Although clinical results are still preliminary, it appears that imaging of pulmonary emboli with SPECT, after administration of radiolabeled thrombus-specific antibody fragments, is accurate and clinically feasible.

»Point-of-Care« D-Dimer Testing

D-dimer testing is efficient in the exclusion of venous thromboembolism (VTE). D-dimer laboratory assays are predominantly performed in centralised laboratories in intra-hospital settings although most patients with suspected VTE are presented in primary care. On the other hand decreasing turnaround time for laboratory testing may significantly improve efficacy in emergency departments. Therefore an introduction of a rapid, easy to perform point of care (POC) assay for the identification of D-dimer may offer improvement in diagnostics flow of VTE both in primary care and emergency departments while it could also improve our diagnostic possibilities in some other severe clinical conditions (e.g. disseminated intra-vascular coagulation (DIC) and aortic aneurism (AA)) associated with increased D-dimer. Several POC D-dimer assays have been evaluated and majority of them have met the criteria for rapid and safe exclusion of VTE. In our hands three assays (Stratus, Pathfast and Cardiac) have the laboratory performance profile comparable with our routine D-dimer laboratory assay (Tinaqaunt).

D-dimer antigen: current concepts and future prospects

The D-dimer antigen is a unique marker of fibrin degradation that is formed by the sequential action of 3 enzymes: thrombin, factor XIIIa, and plasmin. First, thrombin cleaves fibrinogen producing fibrin monomers, which polymerize and serve as a template for factor XIIIa and plasmin formation. Second, thrombin activates plasma factor XIII bound to fibrin polymers to produce the active transglutaminase, factor XIIIa. Factor XIIIa catalyzes the formation of covalent bonds between D-domains in the polymerized fibrin. Finally, plasmin degrades the crosslinked fibrin to release fibrin degradation products and expose the D-dimer antigen. D-dimer antigen can exist on fibrin degradation products derived from soluble fibrin before its incorporation into a fibrin gel, or after the fibrin clot has been degraded by plasmin. The clinical utility of D-dimer measurement has been established in some scenarios, most notably for the exclusion of VTE. This article consists of 2 sections: in the first, the dynamics of D-dimer antigen formation is discussed and an overview of commercially available D-dimer assays is provided. The second section reviews available evidence for the clinical utilization of D-dimer antigen measurement in VTE, as well as emerging areas of D-dimer utilization as a marker of coagulation activation in other clinical settings.

Prognostic value of plasma D-dimer levels in patients with colorectal cancer

OBJECTIVE

Plasma D-dimer levels have been shown to be increased in patients with various solid tumours including lung, prostate, cervical, ovarian, breast and colon cancer. The purpose of this prospective study was to estimate the plasma D-dimer level of patients with colorectal cancer before surgery and to assess whether it has a prognostic value.

METHOD

The study comprised 51 patients with colorectal cancer. Variables including demographic, clinical, operative and pathological findings and routine laboratory tests were recorded. In addition, tumour markers, coagulation tests and plasma D-dimer levels were evaluated.

RESULTS

Histological types other than well-differentiated adenocarcinoma, relatively advanced tumour stage and a high preoperative plasma D-dimer level were the prognostic factors that were associated with shorter postoperative survival according to univariate analyses. The presence of vascular invasion was associated with higher preoperative D-dimer levels. However, there was no statistically significant relationship between postoperative survival and the presence of vascular invasion.

CONCLUSION

Postoperative survival was significantly shorter in colorectal cancer patients with elevated preoperative D-dimer levels. Evaluation of preoperative D-dimer level can be used to predict postoperative survival.

Hemostatic defect in baboons autotransfused treated plasma to simulate shed blood

BACKGROUND

Nonwashed shed blood may contain products of clotting and fibrinolytic, and antifibrinolytic substances. This study was done to determine how autotransfusion of nontreated plasma and plasma treated with urokinase with and without aprotinin affected hemostasis in healthy baboons.

METHODS

A 500-mL volume of blood was collected from the baboon, a 250-mL volume of plasma was isolated, and the RBCs were reinfused. Three baboons were autotransfused untreated plasma. Four baboons received plasma that had been treated with 3000 IU/mL urokinase at +37 degrees C for 30 minutes. Eight baboons received plasma that had been treated first with urokinase 3000 IU/mL at +37 degrees C for 30 minutes and then with aprotinin (1000 KIU/mL). Bleeding time, fibrinogen degradation products (FDP), D-dimer, and alpha-2 antiplasmin levels were measured.

RESULTS

During the 4-hour period following autotransfusion of the urokinase-aprotinin-treated plasma, the levels of D-dimer and FDP were significantly higher and fibrinogen and alpha-2 antiplasmin levels were significantly lower than those levels seen after the autotransfusion of nontreated plasma. FDP and D-dimer levels showed significant positive correlations with prothrombin time (PT) and activated partial thromboplastin time (aPTT). A significant negative correlation was observed between thrombin time (TT) and fibrinogen level. A significant positive correlation was observed between bleeding time and D-dimer level and a significant negative correlation between the bleeding time and the fibrinogen level.

CONCLUSIONS

The infusion of a volume of urokinase or urokinase-aprotinin treated autologous plasma equivalent to 15% of the blood volume was not associated with a bleeding diathesis in healthy baboons.

Safety, pharmacokinetic and dosimetry evaluation of the proposed thrombus imaging agent 99mTc-DI-DD-3B6/22-80B3 Fab'

PURPOSE

(99m)Tc-DI-DD-3B6/22-80B3 (Thromboview, hereafter abbreviated to (99m)Tc-DI-80B3 Fab') is a humanised, radiolabelled monoclonal antibody Fab' fragment with high affinity and specificity for the D-dimer domain of cross-linked fibrin. The purpose of this study was to evaluate the safety, pharmacokinetics and dosimetry of four increasing doses of (99m)Tc-DI-80B3 Fab' in healthy volunteers.

METHODS

Thirty-two healthy volunteers (18-70 years; 16 male, 16 female) received a single intravenous injection of 0.5, 1.0, 2.0 or 4.0 mg of (99m)Tc-DI-80B3 Fab'. Safety outcomes (vital signs, electrocardiography, haematology, biochemistry, adverse events and development of human anti-human antibodies) were assessed up to 30 days post injection. Blood and urine samples were collected up to 48 h post injection. Gamma camera images were acquired at 0.5, 1, 2, 4, 6 and 24 h post injection. Dosimetry was performed using standard MIRD methodology.

RESULTS

No adverse events considered to be drug related were observed. Human anti-human antibody was not detectable in any subject during the follow-up period. (99m)Tc-DI-80B3 Fab' had a rapid initial plasma clearance (t (1/2)alpha=1 h). The pharmacokinetic profile of the Fab' fragment was generally linear across the four dose cohorts. By 24 h, 30-35% of the administered radioactivity appeared in the urine. There was marked renal accumulation with time, but no specific uptake was identified within other normal tissues. The effective dose was 9 mSv/750 MBq.

CONCLUSIONS

(99m)Tc-DI-80B3 Fab' is well tolerated, is rapidly cleared and exhibits clinically acceptable dosimetry-characteristics well suited to a potential thrombus imaging agent.

Novel monoclonal antibody that recognizes new neoantigenic determinant of D-dimer

Our novel monoclonal antibody (mAb) B4 reacted with only D-dimer but not intact fibrinogen, or fibrinogen degradation products (FgDP) such as D-monomer, E fragment on ELISA. B4 didn't react with denatured D-dimer, while it reacted well with denatured D-monomer rather than the native form, indicating that B4 recognizes some neoconformational epitope in D-dimer. In our epitope study, B4 recognized the N-terminal (Bbeta134-142) of D-dimer, which corresponds to the most flexible segment of coiled coil backbone. It was confirmed by inhibition assay of B4 binding to D-dimer using the synthesized peptides with this sequence. As the other evidence, B4 didn't bind to some D-dimer species produced from a particular fibrinogen variant. This fibrinogen variant is mutated BbetaLys133 residue to Gln133 thus it doesn't produce the particular N-terminal epitope of D134 approximately by plasmin. Finally, our mAb was useful for clinical application. ELISA using our mAbs was well correlated with other commercial D-dimer ELISAs and in some clinical samples it was preferable to them. These results suggest that the epitope for B4 is another neoantigenic determinant in native D-dimer as distinct from native D-monomer.

Anticoagulant Therapy for Idiopathic Pulmonary Fibrosis

STUDY OBJECTIVE

To evaluate the effect of anticoagulant therapy on the survival of patients with idiopathic pulmonary fibrosis (IPF).

DESIGN

Prospective study.

SETTING

Five hospitals located in the Miyagi prefecture in Japan, including a university hospital, a Red Cross hospital, two public general hospitals, and a municipal hospital.

PATIENTS

Fifty-six patients with IPF (mean age, 69.4 years; range, 47 to 89) admitted to the hospitals from April 2001 to April 2004.

INTERVENTIONS

Patients were assigned to receive prednisolone alone or prednisolone plus anticoagulant therapy. The anticoagulants included oral warfarin in an outpatient setting and low-molecular-weight heparin for rehospitalized patients with severely progressive respiratory failure.

MEASUREMENTS AND RESULTS

There was no difference in baseline characteristics, including age, gender, clinical condition, pulmonary function, and plasma d-dimer level between the non-anticoagulant group and the anticoagulant group. The overall survival and hospitalization-free periods were assessed. There was a significant difference between survival curves of the non-anticoagulant group and the anticoagulant group, with a 2.9 hazard ratio (p = 0.04, Cox regression model). There was no significant difference in the probability of a hospitalization-free period between groups. The major cause of clinical deterioration was acute exacerbation during follow-up in the present study. Therefore, the mortality and plasma d-dimer levels in patients with an acute exacerbation were also assessed. The mortality associated with acute exacerbations of IPF in the anticoagulant group was significantly reduced compared to that in the non-anticoagulant group (18% vs 71%, respectively; p = 0.008, Fisher Exact Test). Furthermore, the plasma d-dimer levels in patients who died were significantly higher than those in survivors during acute exacerbation of IPF (3.3 +/- 2.3 microg/mL vs 0.9 +/- 0.7 microg/mL, p < 0.0001). Histologic analysis performed in three patients who died due to an exacerbation of IPF in the non-anticoagulant group demonstrated the features of usual interstitial pneumonia and acute lung injury.

CONCLUSIONS

Our data suggested that plasma d-dimer levels are associated with mortality in patients with an acute exacerbation of IPF, and that anticoagulant therapy has a beneficial effect on survival in patients with IPF.

Do Haemostasis Activation Markers that Predict Cardiovascular Disease Exist?

Recognition of the central role of thrombosis in the pathogenesis of cardiovascular disease has prompted growing interest in the association of haemostatic variables with cardiovascular disease. In investigating the predictive value of haemostasis markers, a promising type of measurement is that of the activation products of coagulation and fibrinolysis: prothrombin fragment 1+2 (F1+2), fibrinopeptide A (FPA), soluble fibrin,thrombin-antithrombin (TAT), plasmin-antiplasmin(PAP) complexes and D-dimer. D-dimer was most extensively studied and there is substantial evidence that D-dimer is a strong, consistent predictor of cardiovascular events in the general population and inpatients with cardiovascular disease. Data on other markers are considerably less abundant and more controversial. The prognostic value of these markers remains to be fully defined in future epidemiological and clinical studies.

Monitoring of fibrinolysis parameters during myocardial revascularization according to type of procedure

The aim of the study was to assess the effect of cardiothoracic surgery on the dynamics of plasminogen, D-dimers and plasminogen activator inhibitor (PAI-I) during the first 24h after surgery. The study included 14 patients operated with (on-pump) and 14 without (off-pump) the use of extracorporeal circulation (ECC). Blood sampling was carried out on induction of anesthesia (timepoint 1), on introduction of heparin (point 2) and protamine (point 3), at the end of surgery (point 4), and the next morning (point 5). Relative to point 1, the utilization of plasminogen at point 2 was 24% and 17% in the on-pump and off-pump groups, respectively (p=0.001 both). Increased D-dimer concentration from the baseline was more pronounced in the on-pump group (p=0.001). At point 5, D-dimer concentrations were comparable in both groups and different from baseline levels. PAI-I activity showed within-group differences from baseline at point 5 in the off-pump group (p=0.001), and at points 3 and 5 in the on-pump group (p=0.002 and 0.001, respectively). At point 5, the activity of PAI-I was comparable in both groups, yielding p=0.001 vs. baseline. Fibrinolysis was more pronounced and more dynamic in the on-pump group due to activation of the systemic inflammatory response induced by the use of ECC. In the off-pump group, fibrinolysis was a normal physiological response to the surgical procedure.

Improved imaging of deep venous thrombi during anticoagulation using radiolabelled anti-D-dimer antibodies

OBJECTIVES

Radiolabelled anti-fibrin antibodies have not yet enabled reliable and practical diagnosis of venous thromboembolism. However, previous unsuccessful clinical trials were performed with anti-fibrin beta-chain antibodies that do not optimally bind to thrombi during anticoagulation. The current experiments were performed to determine if radiolabelled anti-D-dimer antibodies more reliably allowed nuclear medicine imaging of deep venous thrombi during anticoagulation than anti-beta-chain antibodies.

METHODS

Dogs with pre-existing unilateral femoral vein thrombi were anticoagulated with heparin (300 units.kg (-1) bolus followed by 90 units.kg(-1).h(-1) continuous infusion). They were then allocated to receive one of three (111)In labelled antibodies: anti-D-dimer, anti-beta or a non-specific control antibody. Gamma scans of the legs were performed at regular intervals for 24 h. Scans were interpreted in a blinded fashion and the number of gamma counts from the femoral area on the thrombosed side was compared to the contralateral side. Clot/blood isotope density ratios were determined post-mortem.

RESULTS

Leg thrombi were 100% detectable in the anti-D-dimer group, but only 60% detectable in the anti-beta group. Mean +/- SD relative counts in the thrombosed femoral area was 137 +/- 10% compared to the contralateral side in the anti-D-dimer group, but only 116 +/- 20% in the anti-beta group. The clot/blood ratio was 24.5 +/- 2.8 in the anti-D-dimer group, but only 7.8 +/- 2.0 in the anti-beta group.

CONCLUSIONS

In labelled anti-D-dimer provides superior nuclear medicine images of thrombi during intensive anticoagulation compared to anti-beta. Clinical results with radiolabelled anti-D-dimer may be more promising than those previously observed with other anti-fibrin antibodies.

Hemostatic markers and the sepsis-related organ failure assessment score in patients with disseminated intravascular coagulation in an intensive care unit

We investigated the correlation between disseminated intravascular coagulation (DIC) score and hemostatic parameters and sepsis-related organ failure assessment (SOFA) score with clinical outcome of patients with DIC in an intensive care unit (ICU). The SOFA score was markedly elevated in patients with DIC relative to patients without DIC and significantly higher in non-survivors than in survivors. Abnormalities in almost all hemostatic parameters were significant in patients with DIC, but there was no significant difference in almost all hemostatic parameters between survivors and non-survivors. However, plasma antithrombin (AT) levels were significantly lower in non-survivors than in survivors. Soluble fibrin (SF) and tissue type plasminogen activator (tPA)-plasminogen activator inhibitor-I (PAI-I) complex correlated significantly with the SOFA score, whereas AT levels correlated significantly and negatively with the SOFA score. We conclude that the SOFA score is useful for predicting outcome in DIC patients in the ICU, and that hemostatic parameters, especially plasma AT levels, are also useful markers for organ failure and clinical outcome.

In Vitro Effects of Poly-N-Acetyl Glucosamine on the Activation of Platelets in Platelet-Rich Plasma with and without Red Blood Cells

BACKGROUND

This study was performed to assess the effect of poly-N-acetyl glucosamine fiber slurry on plasma clotting proteins, platelets, and red blood cells in the clotting of the blood.

METHODS

Citrate phosphate dextrose whole blood was stored at 22degreesC for 48 hours to prepare platelet-poor plasma, platelet-rich plasma (PRP), and PRP plus red blood cells with hematocrit values of 20%, 35%, and 45% with and without an equal volume of poly-N-acetyl glucosamine fibers (1 mg/mL 0.9% NaCl).

RESULTS

Thromboelastogram data show that poly-N-acetyl glucosamine fibers (p-GlcNAc) significantly reduced the R time in platelet-poor plasma, PRP, and PRP supplemented with red blood cells. Poly-N-acetyl glucosamine fibers increased, but not significantly, Annexin V and factor X binding to platelets, platelet microparticles, and red blood cell Annexin V binding. Poly-N-acetyl glucosamine fibers increased the production of thromboxane B2 by PRP.

CONCLUSION

Poly-N-acetyl glucosamine slurry activates platelets.

Single photon emission computed tomography of pulmonary emboli and venous thrombi using anti-D-dimer

Previous attempts to diagnose thromboemboli using radiolabeled antibodies and nuclear medicine imaging have been disappointing. We present the results of experiments with intravenous technetium-99m-labeled deimmunized antifibrin Fab' fragments to diagnose thromboemboli using single photon emission computed tomography (SPECT), a highly sensitive scintigraphic imaging technique. Pulmonary emboli (PEs) and lower extremity deep vein thrombi (DVTs) were formed in five dogs, then technetium-99m-labeled Fab' ( approximately 400 mg, approximately 260 MBq) were injected via forelimb veins. Thoracic and lower extremity SPECT scans were performed at 2-hour intervals after antibody infusion to visualize the thromboemboli. Four hours after antibody infusion, all PEs and DVTs of mass 0.4 g or greater were clearly visualized on SPECT scans as 'hot spots' within the lungs and legs, respectively. PEs (0.48 +/- 0.09 g) were intensely radiolabeled, yielding clot/blood radioactivity ratios of 22.8 +/- 5.6. DVTs (0.45 +/- 0.31 g) also had high clot/blood ratios (11.7 +/- 2.6). Infusion of these radiolabeled antibody fragments, combined with SPECT, produces clear images of PEs and DVTs within a clinically feasible time frame. The technique reliably identified even peripheral thromboemboli of relatively small size, which are difficult to diagnose with currently available imaging techniques, and may enable imaging of PEs, DVTs, or both in the same patient.

Comparison of diagnostic criteria for disseminated intravascular coagulation (DIC): diagnostic criteria of the International Society of Thrombosis and Hemostasis and of the Japanese Ministry of Health and Welfare for overt DIC

We compared the criteria set by the International Society of Thrombosis and Hemostasis (ISTH) for the diagnosis of disseminated intravascular coagulation (DIC) with the criteria of the Japanese Ministry of Health and Welfare (JMHW) set for the diagnosis of overt DIC. We studied 1,284 Japanese patients with DIC. The rate of agreement in the diagnosis of DIC by the two diagnostic systems was 67.4%. In addition, only 2.0% of non-DIC patients by JMHW criteria were diagnosed with overt DIC by ISTH criteria, suggesting that ISTH for overt DIC includes typical cases of DIC. The concordance of diagnosis for DIC by ISTH and JMHW was significantly high in patients with trauma or acute promyelocytic leukemia. About 70% of DIC or overt DIC patients had more than 1 point in the scoring system for prothrombin time, but >50% of those patients had 0 point for plasma fibrinogen level. Abnormal fibrin and fibrinogen degradation product (FDP) levels and platelet counts were observed in >88% of DIC and overt DIC patients but were observed in >50% of non-DIC patients, indicating that these parameters are sensitive markers but not specific markers for the diagnosis of DIC. Considered together, our results suggest that the diagnostic criteria for DIC and overt DIC could be improved by changing the cut-off values of the global coagulation tests.

Changes in functional activities of plasma fibrinogen after treatment with methylene blue and red light

BACKGROUND

Methylene blue (MB) plus light treatment used for virus inactivation of human plasma units may lead to changes in the functional activities of fibrinogen.

STUDY DESIGN AND METHODS

Single-donor units of fresh plasma were treated with 1.0 microM MB and a red light dose of 48 J per cm2. The effects of MB plus red light treatment on fibrinogen clottability, fibrin polymerization and gelation, clot stabilization, and fibrinolysis were studied.

RESULTS

The concentration of clottable fibrinogen was unchanged during MB plus red light treatment, but a light-dose-dependent decrease of the concentration of functional fibrinogen was found. The initial release rate of fibrinopeptide A was slightly increased after MB plus red light treatment. Turbidity measurements of fibrin gel showed prolonged clotting time, lower fibrin fiber mass-to-length ratio, and slightly smaller fiber diameter. At a given clotting time, a gel with lower fibrin fiber mass-to-length ratio was produced. Clot stability and fibrinolysis remained normal. l-Histidine added to plasma before MB plus red light treatment normalized the thrombin-induced coagulation time in a dose-dependent way.

CONCLUSION

MB plus red light treatment affected the polymerization and gelation phase of fibrin. A tighter fibrin gel structure was formed. No effect on stabilization of fibrin clot or fibrinolysis was found.

Disseminated intravascular coagulation current concepts of etiology, pathophysiology, diagnosis, and treatment

The pathophysiologic mechanisms and clinical and laboratory manifestations of DIC are complex, partly because of inter-relationships within the hemostasis system. Only by clearly understanding these extraordinarily complex pathophysiologic inter-relationships can the clinician and laboratory scientist appreciate the divergent and wide spectrum of often-confusing clinical and laboratory findings in patients with DIC. Many therapeutic decisions to be made are controversial and lack validation. Nevertheless, newer antithrombotic agents and agents that can block, blunt, or modify cytokine activity and the activity of vasoactive substances seem to be of value. The complexity and variable degree of clinical expression suggest that therapy should be individualized depending on the nature of DIC, the patient's age, etiology of DIC, site and severity of hemorrhage or thrombosis, and hemodynamics and other appropriate clinical parameters.

Good or poor responses of hemostatic molecular markers in patients with hematopoietic disorders after treatment of disseminated intravascular coagulation

Changes of hemostatic markers in 226 patients with disseminated intravascular coagulation (DIC) and hematopoietic disorders were examined after treatment of DIC. The changes in prothrombin time (PT) ratio, fibrinogen, fibrin and fibrinogen degradation products (FDP), antithrombin, and protein C, thrombin-antithrombin complex (TAT), plasmin-plasmin inhibitor complex (PPIC), and soluble fibrin monomer complex (SFMC) in all patients with DIC were significant during the clinical course of DIC, but those of D-dimer, thrombomodulin (TM), tissue factor (TF), and tissue factor pathway inhibitor (TFPI) were not. Activated partial thromboplastin time (aPTT) and PT were significantly longer in the poor response group than in good response group. Plasma levels of FDP, TAT, PPIC, SFMC, TM, and DIC score were significantly higher in poor response group than in good response. Protein C and antithrombin levels were significantly lower in poor response group than in good response group. The changes of PT ratio, fibrinogen, FDP, DIC score, antithrombin, plasmin inhibitor, and protein C were significant in the good response group, but these levels were not significant in the poor response group. The changes in plasma TAT and SFMC levels were significant in the good response group but were not in poor response group. The changes in D-dimer, TM, TF, or TFPI were not significant in both groups. These findings suggest that anticoagulant agents should be administered at levels below TAT 40 ng/mL or SFMC 300 microgram/mL in patients with DIC and hematopoietic disorders.

The diagnosis of disseminated intravascular coagulation

Disseminated intravascular coagulation (DIC) is a syndrome characterized by systemic intravascular activation of coagulation, leading to widespread deposition of fibrin in the circulation. In recent years, the pathogenetic pathways leading to DIC have been largely identified, which could result in more precise diagnostic tests for this disorder. However, the clinical and laboratory diagnosis of DIC may remain difficult, since routinely available tests do not specifically assess ongoing thrombin generation. Molecular markers for activation of coagulation and fibrinogen to fibrin conversion are highly sensitive but also disappointedly aspecific for the diagnosis of DIC. Moreover, these tests are often not available in most settings for daily clinical care. A combination of widely available tests, however, may be helpful in making the diagnosis of DIC, according to a recently developed algorithm.

Randomized trial of different regimens of heparins and in vivo thrombin generation in acute deep vein thrombosis

Low-molecular-weight and unfractionated heparins are frequently used to treat venous thromboembolism, but it is not known whether they are equally effective in inhibiting in vivo generation of thrombin. In this multicenter trial, 1048 patients were randomized to intravenous unfractionated heparin (group A), twice daily low-molecular-weight heparin (reviparin) for 1 week (group B), or once daily reviparin for 4 weeks (group C). All patients received vitamin K antagonists. Blood samples withdrawn at the baseline and at weeks 1 and 3 were analyzed using markers of in vivo thrombin generation and other coagulation parameters. During the first 3 weeks symptomatic recurrent deep vein thrombosis-pulmonary embolism (DVT/PE) occurred in 17 (4.5%) of 375 patients in group A compared with 4 (1.0%) of 388 patients in group B, and 9 (2.4%) of 374 patients in group C. Forty percent of patients in group A, 53.4% in group B, and 53.5% in group C showed 30% or greater reduction in thrombus size assessed by venography. Patients in group B had significantly greater reduction in D-dimer, prothrombin fragments 1 and 2 (F1 + 2), endogenous thrombin potential (ETP), and thrombin-antithrombin (TAT) complexes compared to groups A and C. Greater release of tissue factor pathway inhibitor (TFPI) and reduction in levels of thrombin activatable fibrinolysis inhibitor (TAFI) and fibrinogen were significantly more pronounced in group C patients. Reviparin administered twice daily plus vitamin K antagonist is more effective in inhibiting in vivo thrombin generation compared to intravenous unfractionated heparin plus vitamin K antagonist, and reviparin once daily produced significantly higher TFPI release and greater reduction in TAFI and fibrinogen levels.