Evaluation of a Soluble Fibrin Assay in Patients with Suspected Deep Vein Thrombosis

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.

Evaluation of hypercoagulability using soluble fibrin monomer complex in sick newborns

BACKGROUND

Soluble fibrin monomer complex (SFMC) and fibrin monomer (FM) are well known as markers for hypercoagulability, but such measurements have not been investigated in detail for the neonate. To identify the presence of a hypercoagulable state in sick newborns, the behavior of SFMC with special reference to those of other coagulation tests, and the relationships with other parameters of blood coagulation as well as lactate, which is considered to be the gold standard for assessing tissue hypoxia, were studied.

METHODS

Records of 216 sick newborns, who had undergone blood coagulation tests, were retrospectively studied based on their medical records.

RESULTS

SFMC had a significant correlation with d-dimer in infants with birthweight <1500 g, but no correlation was observed with prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen, anti-thrombin or platelet count. In contrast, in infants with birthweight ≥ 1500 g, SFMC was correlated with PT, APTT, fibrinogen, and d-dimer, but no correlation was observed with anti-thrombin or platelet count. In addition, SFMC was significantly higher in the high lactate group (lactate ≥ 4 mmol/L), compared with the low lactate group (<4 mmol/L).

CONCLUSION

Measurement of blood SFMC is useful to monitor hypercoagulable state in sick newborns with hypoxia.

Soluble fibrin monomer degradation products as a potentially useful marker for hypercoagulable states with accelerated fibrinolysis

BACKGROUND

Fibrin monomer (FM) and its complex (sFC) exist at high concentrations in hypercoagulable state blood. Two novel immunoassays for sFC (SF and FMC) using specific monoclonal antibodies (IF-43 and F405) were recently developed.

METHODS

We measured the concentrations of thrombotic markers in 103 patients with DIC and thrombotic disorders.

RESULTS

We found that the concentration of FMC was approximately 3.35-fold greater than that of SF. In patients with a high FMC/SF ratio, FDP and D dimer concentrations were increased, suggesting that the discrepancy in sFC concentrations was caused by fibrinolytic activity. Further, plasma samples from those patients were found to contain the X- and Y-fragments of FM in addition to FM and sFC in a Western blotting assay using F405, which binds with those fragments. In an in vitro study, FM formed from pooled plasma containing EDTA was degraded to the X- and Y-fragments of FM by fibrinolytic activity, and we termed those FM degradation products (FMDP).

CONCLUSION

Determination of FMDP is important for diagnosis of thrombogenic conditions associated with fibrinolysis, such as in patients with DIC, and it may serve as a useful marker for hypercoagulable states with accelerated fibrinolysis.

Postmenopausal hormone replacement therapy increases coagulation activity and fibrinolysis

Hormone replacement therapy (HRT) appears to be cardioprotective in postmenopausal women; however, concerns exist over its thrombogenic effects. To address the effects of combined HRT on coagulation and fibrinolysis, we have measured circulating markers of these processes in a double-blind placebo-controlled trial. Forty-two healthy postmenopausal women aged 50 to 75 years received continuous combined HRT with 2 mg estradiol+1 mg norethisterone or placebo for 6 weeks. Hormone profiles were measured at baseline, and lipid and hemostatic parameters were measured at baseline and after 6 weeks of therapy. Baseline characteristics were similar in the 2 groups. With change from baseline the main outcome measure, HRT increased the markers of coagulation (prothrombin fragments 1+2, 0.20+/-0.06 versus 0.06+/-0.04 nmol/L, P=0.0005; soluble fibrin, 2.3+/-0.4 versus 0.25+/-0.3 microgram/mL, P=0.0004), reduced plasma fibrinolytic inhibitory activity (plasminogen activator inhibitor-1, -0.67+/-0.16 versus 0.24+/-0.21 U/mL, P=0.002), and increased fibrinolysis (D-dimer, 24+/-12 versus -6+/-8 ng/mL, P=0.04) compared with placebo. Increases in soluble fibrin and D-dimer were positively correlated (r=0.59, P=0.02), but changes in plasminogen activator inhibitor-1 and D-dimer were unrelated. Although baseline hemostatic and lipid parameters were correlated, there were no associations between changes in hemostatic markers and lipids after treatment. Short-term oral combined continuous HRT (estradiol and norethisterone) increased thrombin and fibrin generation, reduced plasma fibrinolytic inhibitory activity, and increased fibrinolysis. Enhanced fibrinolysis was related to increased fibrin generation but not reduced plasma fibrinolytic inhibitory activity. Coagulation activation may partly explain the increases in venous thrombosis and cardiovascular events reported with the use of combined HRT.

Laboratory diagnosis of venous thromboembolism

Venous thromboembolism is a common medical condition in both out-patients and in-patients. Despite the development of non-invasive tests, the diagnosis of deep vein thrombosis and pulmonary embolism remains a clinical challenge. In an effort to improve diagnostic accuracy and to reduce the necessity of serial testing, laboratory markers of thrombin generation and fibrinolysis have been investigated as first-line screening tests. Although the majority of markers are elevated in acute thrombosis, D-dimer, a specific derivative of cross-linked fibrin, appears to have the most potential clinical utility. Accuracy studies and preliminary management trials suggest that rapid D-dimer enzyme-linked immunosorbent assays and the whole blood agglutination assay, SimpliRED D-dimer (Agen Biomedical, Brisbane, Australia), have strong potential as exclusionary tests in patients with suspected venous thrombosis.

Evaluation of the combination of a bedside D-dimer assay and enzyme-linked immunosorbent soluble fibrin assay in patients with suspected venous thromboembolism

The objectives of the study were to determine whether the combination of a negative SimpliRED D-dimer assay and a low soluble fibrin result reliably excludes venous thromboembolism, and whether patients with proven venous thromboembolism and a normal SimpliRED D-dimer have evidence of impaired fibrinolysis. The study was a retrospective analysis of a cohort of 262 consecutive patients, 94 patients presenting with suspected deep venous thrombosis and 168 with suspected pulmonary embolism. Fifty-nine patients (22.5%) were classified as venous thromboembolism-positive, 27 with pulmonary embolism, and 32 with deep venous thrombosis. One hundred and fourteen patients (43.5%) had SimpliRED D-dimer and a soluble fibrin result of less than or equal to 2.0 microg/ml; the negative predictive value was 98.2% (95% confidence interval: 93.8-99.8%), and the likelihood ratio was 0.06. Eight patients with proven venous thromboembolism had a negative SimpliRED D-dimer; all had elevated ELISA D-dimer levels and six had elevated soluble fibrin levels. This suggests that patients with venous thromboembolism and a normal SimpliRED result do not have impaired fibrinolysis as a cause of their false-negative result. This study suggests that the combination of SimpliRED and soluble fibrin can be used to exclude venous thromboembolism in over 40% of patients who present with a clinical suspicion of deep venous thrombosis or pulmonary embolism and that the small group of patients with venous thromboembolism and a normal SimpliRED do not have impaired fibrinolysis.

Poor correlation between soluble fibrin concentrations measured by two commercially available immunoassays

Soluble fibrin (SF) has attracted considerable interest as a marker for haemostatic activation. Two new enzyme immunoassays for SF, Enzymun-Test FM (Boehringer Mannheim, Germany) and Fibrinostika Soluble Fibrin (Organon Teknika, Belgium) have recently become commercially available. We measured plasma levels of SF in clinically obtained blood samples in order to compare the two new assays. Blood was drawn from 10 healthy volunteers and from 149 patients on the first day after surgery for fractures of the upper part of the femur. Collection and processing was done according to the manufacturers' recommendations. In the patients, levels found by the two assays were significantly different. The Enzymun-Test assay reported a median (range) of 11.87 (2.66 - > 62.20) mg/l, whereas the Fibrinostika assay found a median (range) of 3.34 (1.08 - >10) mg/l. The correlation coefficient was 0.38 (Spearman). A poor correlation was thus found between values obtained by the two assays in the patient category chosen. Further validation of the assays is necessary.