Thrombophilia testing: what do we think the tests mean and what should we do with the results?
Explore the source record for details and available documents.
Anticoagulants↗
Biomedical subjects
T Baglin
Publications and source records attributed to T Baglin.
The factor V R2 allele: risk of venous thromboembolism, factor V levels and resistance to activated protein C.
Case-control studies have yielded conflicting results regarding the relative risk of venous thromboembolism associated with the factor V R2 allele. We calculated odds ratios in 581 patients and 469 age-matched controls. The odds ratio for the R2 allele in patients relative to controls was 1.21 (95% CI 0.84 to 1.74). These results do not support the hypothesis that the R2 allele is a risk factor for venous thromboembolism. There was no relationship between factor V levels and R2 carrier status. Normalised APC sensitivity ratios were not lower in carriers of the R2 allele. In an in vitro model progressive APC resistance was observed with factor V levels of 60% and less but ratios less than 2.4 (equivalent to a normalised ratio of 0.73) did not occur until factor V levels were less than 20%. The relationship between APC resistance and factor V level was not observed in a factor VIII-independent model.
Activated Protein C Resistance↗
Lupus anticoagulant testing with optical end point automation.
The dilute Russell viper venom time and kaolin clotting time (KCT) are very sensitive screening tests for lupus anticoagulant activity. However, due to the high turbidity of the kaolin reagent it is difficult to accommodate the KCT on the optical end point automation of today. We evaluated five recently reported screening tests (the silica clotting time, the Textarin/Ecarin ratio, the Taipan venom time, the factor V ratio, and a kaolin clotting time using low-turbidity kaolin) as potential alternatives to the KCT. The sensitivity and specificity of the silica clotting time compared well to KCT, detecting 10/12 KCT positive samples and showing equal sensitivity to dilution of lupus positive plasma. In addition, the silica clotting time allows for a confirmatory phospholipid correction procedure. False-positive results were seen in 2 of 15 warfarinised samples. A second assay utilising the ratio of extrinsic/intrinsic factor V assays was not affected by either warfarin or heparin. This assay also gave positive results with 3 of 23 samples previously screened as lupus negative but exhibiting anticardiolipin positivity. It was therefore concluded that a combination of the silica clotting time and dilute Russell viper venom time met the requirements of lupus sensitivity with demonstration of phospholipid dependence and optical end point compatibility. The factor V ratio is a useful second-line screen for both anticoagulated patients and anticardiolipin antibody-positive samples.
Anticoagulants↗
Activated protein C resistance: effect of platelet activation, platelet-derived microparticles, and atherogenic lipoproteins.
Plasma and platelet factor Va represent different substrates for activated protein C (APC). In this study, we have measured platelet-dependent APC resistance and the effect of aspirin and a platelet glycoprotein IIbIIIa antagonist (GR144053F) on this phenomenon. In platelet rich plasma (PRP), progressive APC resistance was observed with increasing platelet activation. APC sensitivity ratios of 1.8, 1.7, and 1.4 were observed after platelet activation with thrombin receptor activating peptide (TRAP), collagen, and A23187, respectively. Ultracentrifugation at 77,000g for 1 hour abolished APC resistance indicating that the phenotype is associated exclusively with the platelet membrane. APC resistance was not observed in the presence of phosphatidylcholine-phosphatidylserine (PCPS) vesicles or purified human plasma lipoproteins. APC resistance was observed in the presence of platelet-derived microparticles, but to a lesser degree than that in the presence of activated platelets. The platelet-dependent APC resistance phenotype was also observed when endogenous APC was generated by Protac (American Diagnostica, Inc, Greenwich, CT). In vitro inhibition of platelet activation with aspirin had no effect, but the fibrinogen receptor antagonist, GR144053F, inhibited platelet-dependent APC resistance. These results indicate that platelet activation results in an APC-resistant phenotype comparable to that observed in the plasma of patients with factor V gene mutations affecting critical APC cleavage sites. This suggests that platelet activation at the site of endothelial damage downregulates a critical natural anticoagulant mechanism. The antithrombotic effect of aspirin may be due to an indirect effect on platelet-dependent APC resistance with reduced platelet retention within a developing thrombus. The more potent antithrombotic effect of glycoprotein IIbIIIa antagonists may in addition be the result of reduced platelet factor Va expression and modulation of the platelet-dependent APC resistance phenotype.
Activated Protein C Resistance↗
Anticoagulation may be beneficial in high risk factor V Leiden carriers.
Explore the source record for details and available documents.
Anticoagulants↗
Factor V Cambridge: a new mutation (Arg306-->Thr) associated with resistance to activated protein C.
A new factor V mutation associated with resistance to activated protein C and thrombosis (factor V Cambridge, Arg306-->Thr) was found in one patient from a carefully selected group of 17 patients with venous thrombosis and confirmed APC resistance in the absence of the common Gln506 mutation. The Arg306 mutation was also present in a first degree relative who also had APC resistance. Other potential causes of APC resistance, such as a mutation at the Arg679 site and the factor V HR2 haplotype, were excluded. Subsequent screening of 585 patients with venous thromboembolism and 226 blood donors did not show any other individual with this mutation. Factor VThr306 is the first description of a mutation affecting the Arg306 APC cleavage site and is the only mutation, other than factor V Leiden (Arg506-->Gln), that has been found in association with APC resistance. This finding confirms the physiologic importance of the Arg306 APC-cleavage site in the regulation of the prothrombinase complex. It also supports the concept that APC resistance and venous thrombosis can result from a variety of genetic mutations affecting critical sites in the factor V cofactor.
Arginine↗
Management of warfarin (coumarin) overdose.
Treatment with coumarin oral anticoagulants, such as warfarin, is effective antithrombotic therapy, but patients treated with these drugs are at significant risk of bleeding. The risk of haemorrhage increases with increasing intensity of anticoagulation and overanticoagulation is common. Reversal can be achieved by stopping the coumarin drug or administration of vitamin K, fresh frozen plasma or coagulation factor concentrates. However, there are surprisingly few studies defining the optimum dose of these products and there are no randomized studies comparing the relative benefit and risk of coagulation factor concentrates versus fresh frozen plasma. Guidelines for the management of overdose are based on level III and IV evidence and are, therefore, only grade B recommendations at best. Further studies are required to determine the most effective use of products and the dose required for safe reversal of overanticoagulation.
Anticoagulants↗
Internal jugular vein thrombosis in association with the factor V Leiden mutation.
We report an unusual case of internal jugular vein thrombosis in a 57-year-old female, with the recently discovered factor V Leiden (FVR506Q) mutation. The molecular basis of this mutation is described, and the importance of screening for hereditary venous thrombotic states is emphasized.
Factor V↗
Risk of recurrent venous thromboembolism in patients with the factor V Leiden (FVR506Q) mutation: effect of warfarin and prediction by precipitating factors. East Anglian Thrombophilia Study Group.
Three cohorts of patients with the factor V Leiden mutation were recruited independently (heterozygotes, homozygotes and combined thrombophilia). The antithrombotic efficacy of oral anticoagulation and the predictive value for recurrence of an idiopathic as opposed to a precipitated first event were determined. Idiopathic first events occurred at an older age than precipitated events (43 v 26 years, LR = 23.31, P < 0.001). None of the patients had a recurrent event while on warfarin but the median time to recurrence after stopping warfarin was 9 years (95% CI 0.7-17.3 years). The time to recurrence was shorter when the first event was idiopathic as opposed to precipitated (3.5 v 13 years, LR = 4.76, P = 0.029). A calculation of benefit to risk of oral anticoagulation with a target INR of 2.5 does not support the use of long-term therapy in all patients with the factor V Leiden mutation following a first thrombotic event.
Adolescent↗
A common polymorphism in the tumour necrosis factor-alpha gene associated with high TNF levels is not a risk factor for venous thromboembolism.
The odds ratio of homozygosity or heterozygosity for the TNF2 polymorphism in 575 patients with venous thromboembolism compared to controls was found to be 1.0 (95% CI 0.4-2.1) and 1.1 (95% CI 0.8-1.4) respectively. Comparing subgroups of patients and controls with the factor V Leiden mutation the odds ratio for the TNF2 polymorphism was 0.7 (95% CI 0.2-2.2). Despite evidence of a link between high tumour necrosis factor (TNF) levels and hypercoagulability, our results do not indicate a link between the genetic regulation of TNF production and venous thromboembolic disease.
Adolescent↗
Prevention of central venous catheter associated thrombosis using minidose warfarin in patients with haematological malignancies.
Thrombosis is a well-recognized complication following insertion of central venous catheters and is associated with significant morbidity. In an attempt to reduce line-associated thrombosis, 108 consecutive patients with haematological malignancies were commenced on prophylactic 'minidose' warfarin, 1 mg/d, at the time of line insertion. This group of patients were compared with a historic group of 115 consecutive patients who had not received warfarin. Clinically-suspected venous thrombosis was confirmed by Doppler ultrasound or venography. Patients taking prophylactic warfarin had their prothrombin time measured three times per week with the aim of maintaining an INR <1.6. Five (5%) of the 108 patients who received minidose warfarin developed a thrombosis, at a median of 72 d (range 5-166) from the time of catheter insertion. In the 115 patients who were not anticoagulated 15 (13%) developed a catheter-associated thrombosis at a median of 16 d (range 1-35). There was a significant reduction in line-associated thrombosis in patients receiving warfarin (P=0.03). These data suggest that minidose warfarin reduces the incidence of central venous catheter related thrombosis in patients with haematological malignancies.
Adult↗
Effect of the MTHFRC677T variant on risk of venous thromboembolism: interaction with factor V Leiden and prothrombin (F2G20210A) mutations.
Odds ratios for the MTHFRC677T variant were determined in a large case-control study of 558 unselected patients with venous thromboembolism and 500 control subjects. The odds ratios for MTHFRC677T heterozygosity and homozygosity were 1.07 (95%CI 0.84-1.36) and 0.71 (95%CI 0.48-1.03). In patients with the factor V Leiden or the F2G20210A mutations there was no apparent increase in risk of venous thromboembolism due to the MTHFRC677T polymorphism. Thrombophilia testing should not include genotyping for the MTHFRC677T polymorphism.
Adolescent↗
Analysis of risk factors for over-anticoagulation in patients receiving long-term warfarin.
A cohort of patients with an INR >7.0 were identified prospectively and compared with a group of patients with stable anticoagulant control. During the study 15,100 INR measurements were recorded and 31 (0.2%) were >7.0. Odds ratios of patient characteristics were calculated as an estimate of relative risk for the development of a high INR. The highest risk factor was a target INR of 3.5 (OR 7.3, 95% CI 2.6-20.2). The second highest risk factor was antibiotic therapy in the 4 weeks preceding the high INR (OR 6.2, 95% CI 1.4-27.7). Bleeding was reported more frequently in the high INR group (OR 5.4, 95% CI 2.1-13.9). Five major bleeds occurred in this group compared to none in the stable group. This analysis identifies risk factors for over-anticoagulation and hence when to intensify monitoring and when to consider pre-emptive warfarin dose reductions.
Adult↗
Decentralised anticoagulant care.
Explore the source record for details and available documents.
Anticoagulants↗
Is a change of factor VIII product a risk factor for the development of a factor VIII inhibitor?
Explore the source record for details and available documents.
Aged↗
The effect of delayed analysis or freeze-thawing on the measurement of natural anticoagulants, resistance to activated protein C and markers of activation of the haemostatic system.
We provide a centralised thrombophilia screening service with sample transfer by courier or first class mail, a practice common to many centres. Sample quality is of prime importance, thus we have assessed the effect of delayed sample handling upon the haemostatic variables within our thrombophilia profile. This comprises screening for familial natural anticoagulant deficiency and APC resistance (1-4), and acquired lupus anticoagulant (5,6). The effect upon hypercoagulable markers were also assessed to facilitate evaluation of these in prospective clinical studies (7).
Anticoagulants↗
Risk of venous thromboembolism associated with a G to A transition at position 20210 in the 3'-untranslated region of the prothrombin gene.
The odds ratio for the FII 20210G/A mutation in 504 patients with venous thromboembolism compared to controls was 2.0 (95% CI 1.0-4.0) and, for factor V Leiden, 5.8 (95% CI 3.3-10.3). 3/504 patients were heterozygous for both mutations. None of the patients had combined natural anticoagulant deficiency and the FII 20210G/A mutation. We conclude that the FII 20210G/A mutation is present in 2.6% of the population and the relative risk of venous thromboembolism in carriers is 2.0.
Factor V↗
The role for liver biopsy in haemophiliacs infected with the hepatitis C virus.
Assessment of chronic hepatitis C virus infection requires a liver biopsy in most circumstances. There is a reluctance to perform liver biopsy in haemophiliacs because of a perceived risk of haemorrhage, although with adequate factor concentrate replacement in patients without factor concentrate inhibitors it should be safe. We report a 4-year experience of liver biopsy in patients with haemophilia infected with chronic hepatitis C virus. Of 55 patients seropositive for anti-HCV, 35 have undergone liver biopsy; the median age of this group was 33 years (range 13-68). Seven patients had a normal liver. 22 had portal tract inflammation, four with lymphoid aggregates. Mild piece-meal necrosis was observed in only two and no bile duct injury was found. 11 patients had mild mixed micro- and macro-vesicular fat. 19 patients had no evidence of fibrosis despite an estimated median duration of disease of 20 years (range 8-43). In the remaining 16 patients the maximum degree of fibrosis achieved was stage III. Patients with more significant fibrosis could not be identified on the basis of ALT or HCV RNA. There were no complications of liver biopsy in this series. Liver biopsy following a well-defined protocol in chronic hepatitis C virus haemophiliac carriers is safe in the absence of factor concentrate inhibitors. In this young group of patients without HIV infection there was no evidence of significant liver disease despite a considerable duration of disease. Performing liver biopsy allows accurate information to be given to the patient and avoids unnecessary therapy. The relative youth of this group may be important in the light of the benign histology.
Adolescent↗