Activated Protein C Resistance Assay Detects Thrombotic Risk Factors Other Than Factor V Leiden

Thrombophilia Screening: Not So Straightforward

Although inherited thrombophilias are lifelong risk factors for a first thrombotic episode, progression to thrombosis is multifactorial and not all individuals with inherited thrombophilia develop thrombosis in their lifetimes. Consequently, indiscriminate screening in patients with idiopathic thrombosis is not recommended, since presence of a thrombophilia does not necessarily predict recurrence or influence management, and testing should be selective. It follows that a decision to undertake laboratory detection of thrombophilia should be aligned with a concerted effort to identify any significant abnormalities, because it will inform patient management. Deficiencies of antithrombin and protein C are rare and usually determined using phenotypic assays assessing biological activities, whereas protein S deficiency (also rare) is commonly detected with antigenic assays for the free form of protein S since available activity assays are considered to lack specificity. In each case, no single phenotypic assay is capable of detecting every deficiency, because the various mutations express different molecular characteristics, rendering thrombophilia screening repertoires employing one assay per potential deficiency, of limited effectiveness. Activated protein C resistance (APCR) is more common than discrete deficiencies of antithrombin, protein C, and protein S and also often detected initially with phenotypic assays; however, some centres perform only genetic analysis for factor V Leiden, as this is responsible for most cases of hereditary APCR, accepting that acquired APCR and rare F5 mutations conferring APCR will go undetected if only factor V Leiden is evaluated. All phenotypic assays have interferences and limitations, which must be factored into decisions about if, and when, to test, and be given consideration in the laboratory during assay performance and interpretation. This review looks in detail at performance and limitations of routine phenotypic thrombophilia assays.

Factor V Leiden-independent activated protein C resistance: Communication from the plasma coagulation inhibitors subcommittee of the International Society on Thrombosis and Haemostasis Scientific and Standardisation Committee

Activated protein C resistance (APC-R) due to the single-nucleotide polymorphism factor V Leiden (FVL) is the most common cause of hereditary thrombophilia. It is found predominantly in Caucasians and is uncommon or absent in other populations. Although FVL is responsible for >90% of cases of hereditary APC-R, a number of other F5 variants that also confer various degrees of APC-R and thrombotic risk have been described. Acquired APC-R due to increased levels of coagulation factors, reduced levels of inhibitors, or the presence of autoantibodies occurs in a variety of conditions and is an independent risk factor for thrombosis. It is common for thrombophilia screening protocols to restrict assessment for APC-R to demonstrating the presence or absence of FVL. The aim of this Scientific and Standardisation Committee communication is to detail the causes of FVL-independent APC-R to widen the diagnostic net, particularly in situations in which in vitro APC-R is encountered in the absence of FVL. Predilution clotting assays are not FVL specific and are used to detect clinically significant F5 variants conferring APC-R, whereas different forms of acquired APC-R are preferentially detected using the classical activated partial thromboplastin time-based APC-R assay without predilution and/or endogenous thrombin potential APC-R assays. Resource-specific recommendations are given to guide the detection of FVL-independent APC-R.

Laboratory Testing for Activated Protein C Resistance (APCR): An Update

Activated protein C resistance (APCR) reflects a hemostatic state defined by a reduced ability of activated protein C (APC) to affect an anticoagulant response. This state of hemostatic imbalance is characterized by a heightened risk of venous thromboembolism. Protein C is an endogenous anticoagulant that is produced by the hepatocytes and undergoes proteolysis-mediated activation to APC. APC in turn degrades activated Factors V and VIII. APCR describes a state of resistance by activated Factors V and VIII to APC-mediated cleavage of these factors, thereby promoting amplified thrombin production and a potentially procoagulant state. This resistance of APC may be inherited or acquired. Mutations in Factor V are responsible for the most frequent form hereditary APCR. The predominant mutation, a G1691A missense mutation at Arginine 506, the so-called Factor V Leiden [FVL], causes a deletion of an APC-targeted cleavage site in Factor Va, thereby rendering it resistant to inactivation by APC. There are a variety of laboratory assays for APCR, but this chapter focuses on a procedure using a commercially available clotting assay that utilizes a snake venom and ACL TOP analyzers.

Laboratory Testing for the Evaluation of Phenotypic Activated Protein C Resistance

Activated protein C (APC) resistance (APCR) is considered a risk factor of venous thromboembolism (VTE). The most common genetic disorder conferring APCR is a factor (F) V Leiden mutation, but many other factors are also implicated, such as other F5 mutations (e.g., FV Hong-Kong and FV Cambridge), protein S deficiency, elevated factor VIII, exogenous hormone use, pregnancy and postpartum, depending on how APCR is defined. Considering the large population affected, the detection of this phenotype is crucial. Two types of tests are currently available: clotting time-based assays (with several versions) and thrombin generation-based assays with the endogenous thrombin potential (ETP)-based assay. The purpose of this review is therefore to discuss the performances of these tests and the cases in which it would be appropriate to use one over the other. Initially, as APCR was thought to be solely related to the FV Leiden mutation, the objective was to obtain a 100% specific assay. Clotting-time based assays were thus specifically designed to detect this inherited condition. Later on, an APCR condition without a FV Leiden mutation was identified and highlighted as an independent risk factor of VTE. Therefore, the development of a less specific assay was needed and a global coagulation test was proposed, known as the ETP-based APCR assay. In light of the above, these tests should not be used for the same purpose. Clotting time-based assays should only be recommended as a screening test for the detection of FV mutations prior to confirmation by genetic testing. On the other hand, the ETP-based APC resistance assay, in addition to being able to detect any type of APCR, could be proposed as a global screening test as it assesses the entire coagulation process.

Laboratory Testing for the Evaluation of Phenotypic Activated Protein C Resistance

Activated protein C (APC) resistance (APCR) is considered a risk factor of venous thromboembolism (VTE). The most common genetic disorder conferring APCR is a factor (F) V Leiden mutation, but many other factors are also implicated, such as other F5 mutations (e.g., FV Hong-Kong and FV Cambridge), protein S deficiency, elevated factor VIII, exogenous hormone use, pregnancy and postpartum, depending on how APCR is defined. Considering the large population affected, the detection of this phenotype is crucial. Two types of tests are currently available: clotting time-based assays (with several versions) and thrombin generation-based assays with the endogenous thrombin potential (ETP)-based assay. The purpose of this review is therefore to discuss the performances of these tests and the cases in which it would be appropriate to use one over the other. Initially, as APCR was thought to be solely related to the FV Leiden mutation, the objective was to obtain a 100% specific assay. Clotting-time based assays were thus specifically designed to detect this inherited condition. Later on, an APCR condition without a FV Leiden mutation was identified and highlighted as an independent risk factor of VTE. Therefore, the development of a less specific assay was needed and a global coagulation test was proposed, known as the ETP-based APCR assay. In light of the above, these tests should not be used for the same purpose. Clotting time-based assays should only be recommended as a screening test for the detection of FV mutations prior to confirmation by genetic testing. On the other hand, the ETP-based APC resistance assay, in addition to being able to detect any type of APCR, could be proposed as a global screening test as it assesses the entire coagulation process.

Laboratory Testing for the Evaluation of Phenotypic Activated Protein C Resistance

Activated protein C (APC) resistance (APCR) is considered a risk factor of venous thromboembolism (VTE). The most common genetic disorder conferring APCR is a factor (F) V Leiden mutation, but many other factors are also implicated, such as other F5 mutations (e.g., FV Hong-Kong and FV Cambridge), protein S deficiency, elevated factor VIII, exogenous hormone use, pregnancy and postpartum, depending on how APCR is defined. Considering the large population affected, the detection of this phenotype is crucial. Two types of tests are currently available: clotting time-based assays (with several versions) and thrombin generation-based assays with the endogenous thrombin potential (ETP)-based assay. The purpose of this review is therefore to discuss the performances of these tests and the cases in which it would be appropriate to use one over the other. Initially, as APCR was thought to be solely related to the FV Leiden mutation, the objective was to obtain a 100% specific assay. Clotting-time based assays were thus specifically designed to detect this inherited condition. Later on, an APCR condition without a FV Leiden mutation was identified and highlighted as an independent risk factor of VTE. Therefore, the development of a less specific assay was needed and a global coagulation test was proposed, known as the ETP-based APCR assay. In light of the above, these tests should not be used for the same purpose. Clotting time-based assays should only be recommended as a screening test for the detection of FV mutations prior to confirmation by genetic testing. On the other hand, the ETP-based APC resistance assay, in addition to being able to detect any type of APCR, could be proposed as a global screening test as it assesses the entire coagulation process.

Thrombophilia Caused by Beta2-Glycoprotein I Deficiency: In Vitro Study of a Rare Mutation in APOH Gene

This study aimed to explore the mechanism of a novel mutation (p.Lys38Glu) in apolipoprotein H (APOH) gene causing hereditary beta2-glycoprotein I (β2GPI) deficiency and thrombosis in a proband with thrombophilia. The plasma level of β2GPI was measured by ELISA and Western blotting, and anti-β2GPI antibody by ELISA. Lupus anticoagulant (LA) was assayed using the dilute Russell viper venom time. Deficiency of the major natural anticoagulants including protein C (PC), protein S (PS), antithrombin (AT) and thrombomodulin (TM) was excluded from the proband. A mutation analysis was performed by amplification and sequencing of the APOH gene. Wild type and mutant (c.112A>G) APOH expression plasmids were constructed and transfected into HEK293T cells. The results showed that the thrombin generation capacity of the proband was higher than that of the other family members. Missense mutation p.Lys38Glu in APOH gene and LA coexisted in the proband. The mutation led to β2GPI deficiency and thrombosis by impairing the protein production and inhibiting the platelet aggregation. It was concluded that the recurrent thrombosis of the proband is associated with the coexistence of p.Lys38Glu mutation in APOH gene and LA in plasma.

Laboratory Testing for Activated Protein C Resistance (APCR)

Activated protein C resistance (APCR) describes a hemostatic disorder characterized by a poor anticoagulant response to activated protein C (APC). This results in an increased risk of venous thrombosis, including deep vein thrombosis and pulmonary embolism. Protein C is a natural anticoagulant that is synthesized in the liver and is activated to APC via proteolysis. APC then degrades Factors Va and VIIIa. APCR describes the reduced inability of APC to cleave Factors Va and VIIIa, which therefore promotes increased thrombin generation and potentially leads to a prothrombotic state. APCR may be hereditary or acquired. The most common hereditary defect is due to mutations in Factor V, predominantly the Factor V Leiden [FVL] mutation-a G1691A missense mutation at Arginine 506 that results in its replacement by a glutamine [R506Q] and the abolition of an APC inactivation cleavage site in Factor Va. Laboratory testing for APCR may be undertaken by a variety of methods, but this chapter describes an automated procedure using a commercial Russell Viper Venom-based clotting assay, and using CS-5100 and STA-R analyzers.

The Predictability of Factor V Leiden (FV:Q506) Gene Mutation via Clotting-Based Diagnosis of Activated Protein C Resistance

After the discovery of activated protein C resistance (APCR) due to factor V Leiden mutation and the causal relationship of the phenomenon with clinical thromboembolism, a wide variety of functional clotting-based assays were developed for testing of APCR in relation to the specific DNA-based analysis of FV:Q506 Leiden. The aim of this study is to assess a clotting-based APCR assay using procoagulant crotalidae snake venom with respect to the sensitivity, specificity, and predictability for the presence of the factor V Leiden mutation. APCR testing and factor V DNA analyses have been performed concurrently on 319 patient specimens. APCR values of the patients with homozygous factor V Leiden mutation (70.4±13.5 s) were significantly lower (p<0.001) in comparison to the subjects with the heterozygous mutation (87.6±13.4 s). The assay is highly sensitive (98.7%) and specific (91.9%) for the screening of factor V Leiden mutation. The sensitivity and specificity of the APCR testing reached to 100% below the cut-off value of 120 s among the patients with homozygous factor V Leiden mutation. Therefore, this method could help the desired effective optimal screening strategy for the laboratory search of hereditary thrombophilia focusing on the diagnosis of APCR due to FV:Q506.

An improved algorithm for activated protein C resistance and factor V Leiden screening

OBJECTIVES

To evaluate the performance of a Russell viper venom-based activated protein C resistance (APCR) screening test relative to DNA analysis for the factor V Leiden mutation.

METHODS

We evaluated the concordance between Pefakit APCR screening results and DNA analysis for 435 patients homozygous (n = 11), heterozygous (n = 310), or wild-type (n =114) for the G1691A allele.

RESULTS

Using receiver operating characteristic analysis, we found that a cutoff of 1.89 for the APCR ratio yields a sensitivity and specificity of 99.1%. In patients with discrepant genotype-phenotype correlation, their APCR may provide a more clinically relevant result.

CONCLUSIONS

We compared several strategies for employing reflex testing and found that performing initial APCR screening followed by confirmatory molecular analysis on a subset of cases in the borderline regions between the diagnostic groups can reduce unnecessary testing by approximately 80% without compromising diagnostic accuracy.

[Activated protein C resistance and factor V Leiden: clinical interest]

Activated protein C resistance (APCR) is a coagulation abnormality often linked to FV Leiden mutation, a single nucleotide G1691A substitution resulting in arginine 506→glutamine missense factor V mutation. FV Leiden has a frequency of 20 to 30% in groups of patients with venous thrombosis while it is of 4 to 10% in normal subjects. FV Leiden is considered as a weak risk factor of thrombosis except in homozygote. FV Leiden is implicated in deep venous thrombosis occurrence. Duration of oral anticoagulant treatment is six months in patients developing a first venous thrombosis except in patients with combined defects or a clinical context suggesting a high risk of severe relapse. Detection of APCR by coagulation methods is often used in first intention with a high specificity if plasmas tested are diluted in factor V deficient plasma. Genotyping study is essential to establish the heterozygote or homozygote statute and certain teams perform it directly. Nevertheless, APCR not related to FV Leiden could be an independent thrombosis risk factor. APCR and FV Leiden are included in laboratory investigations of thrombophilic markers in patients less than 50 years with venous thrombosis. In arterial thrombosis, FV Leiden implication is weak or absent. FV Leiden increases the risk of thrombosis in other situations as in patients with cancer. An association with recurrent miscarriages and other vasculoplacental complications is also reported in many studies but the data concerning the efficacy of antithrombotic treatment to prevent recurrence are currently insufficient.

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.

Should patients with venous thromboembolism be screened for thrombophilia?

In the mid-19th century, Virchow identified hypercoagulability as part of the triad leading to venous thrombosis, but the specific causes of hypercoagulability remained a mystery for another century. The first specific cause to be identified was antithrombin III deficiency. Many other causes of thrombophilia, both genetic and acquired, have been discovered since then. The 2 most common genetic causes of thrombophilia are the Leiden mutation of factor V and the G20210A mutation of prothrombin. The most common acquired cause is antiphospholipid syndrome. These factors increase the relative risk of an initial episode of venous thromboembolism (VTE) by a factor of 2 to 10, but the actual risk remains relatively modest. Therefore, thrombophilia screening to prevent initial episodes of VTE is not indicated, except possibly in women with a family history of idiopathic VTE who are considering oral contraceptive therapy. Some physicians screen for thrombophilia to aid decision making concerning the duration of anticoagulant therapy. However, several studies have demonstrated that, with the exception of antiphospholipid syndrome, thrombophilia does not significantly increase the risk of recurrent VTE. On the other hand, idiopathic VTE significantly increases the risk of recurrence in patients with or without thrombophilia.

Amaurosis fugax caused by heritable thrombophilia-hypofibrinolysis in cases without carotid atherosclerosis: thromboprophylaxis prevents subsequent transient monocular partial blindness

Nineteen patients (age 60 +/- 14) with amaurosis fugax associated with heritable thrombophilia-hypofibrinolysis without ipsilateral atherosclerotic carotid plaque or other causes of amaurosis fugax were studied. Our hypothesis was that case-specific thromboprophylaxis would prevent subsequent amaurosis fugax episodes. Prospective treatment data were available for 13 cases. Thrombophilic disorders included high Factors VIII and XI, G20210A prothrombin heterozygosity, low proteins C and S, MTHFR mutations, and the PL A1/A2 mutation. Hypofibrinolytic disorders included plasminogen activator inhibitor-1 4G4G, and high lipoprotein (a). Treatments included Coumadin; Lovenox, folic acid-vitamin B6-vitamin B12, discontinuation of estrogens-selective estrogen receptor modulators, Glucophage, and aspirin, as appropriate. Usually within 1 month on therapy, patients became asymptomatic and have remained asymptomatic for > or = 1 year on therapy, without adverse treatment side effects. When amaurosis fugax occurs without carotid artery atherosclerosis or other known causes, thrombophilia or hypofibrinolysis, or both are nearly universal, safely treatable, reversible pathoetiologies.

Effect on routine and special coagulation testing values of citrate anticoagulant adjustment in patients with high hematocrit values

Recommendations to adjust citrate concentration for blood coagulation specimens with high hematocrit values are based on indirect experimental studies and not direct studies of patient samples with high hematocrit values. We compared the effect of adjusted and non-adjusted citrate concentrations on coagulation test results in samples from 28 patients with high hematocrit values (55%-72% [0.55-0.72]). Prothrombin time (PT) and activated partial thromboplastin time (aPTT) results from nonadjusted and adjusted samples were statistically different and exponentially increased with increasing hematocrit values. Results for fibrinogen, factor VIII, and protein C activity were statistically different and increased linearly with increasing hematocrit values; however, the difference was not as clinically significant. The protein C antigen value increased with increasing hematocrit values but was not significant. The effects on PT and aPTT are due to a dilutional effect of plasma and an interference effect of the higher final citrate concentration on the clotting test result. For patients with high hematocrit values, citrate concentrations must be adjusted for accurate results.

[Association of tow thrombotic risk factors: factor V Leiden and hyperhomocysteinemia. A case report]

The identification of constitutional and/or acquired risk factor is of major importance in the treatment of thromboembolic disease in young people; it contributes to evaluate the risk of recurrence and to define the period of oral prophylactic anticoagulant treatment. Several congenital or acquired abnormalities of haemostasis are actually defined. In this paper, we report the case of a 34-year-old man who developed a deep venous thrombosis, five months before the diagnosis of megaloblastic anemia, probably due to pernicious anemia. The thrombosis was partially explained by the acquired hyperhomocysteinemia induced by vitamin B12 deficiency. Moreover, activated protein C resistance due to factor V Leiden, was revealed in our patient. This latter improved under anticoagulant treatment combined with vitamin B12. Combination in one individual, of different risk factors predisposing to inherited and/or acquired thrombophilia, results in increased risk for thrombo-embolic disease, suggesting synergic interaction between these factors.

Amaurosis fugax: associations with heritable thrombophilia

The aim of this study was to prospectively assess associations between amaurosis fugax, inherited thrombophilia, and acquired thrombophilia. Thrombophilia and hypofibrinolysis were studied in 11 cases (eight women, three men; all white) with amaurosis fugax, 57 +/- 17 years old, selected by the absence of abnormal brain magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), magnetic resonance venography (MRV), ipsilateral internal carotid artery plaque, atrial fibrillation, or cardiac thrombus. Cases were compared to 78 healthy adult white controls (53 +/- 18 years old) for serologic measures, and by polymerase chain reaction to 248 healthy white controls (78 adults, 170 children) for gene mutations. All 11 cases had one or more familial thrombophilic coagulation disorder including one heterozygous for the G1691A factor V Leiden mutation, two with low free protein S, four with high factor VIII, three with resistance to activated protein C, three homozygous for the C677T methylenetetrahydrofolate reductase (MTHFR) mutation, two compound C677T-A1298C MTHFR heterozygotes, and three with hypofibrinolytic 4G4G homozygosity for the PAI-1 gene. The case with factor VIII of 160% had two other thrombophilias (compound MTHFR C677T-A1298C heterozygosity, resistance to activated protein C), and hypofibrinolytic high Lp(a). Thrombophilic C677T MTHFR homozygosity or compound C677T-A1298C heterozygosity was present in five of 10 (50%) cases vs. 30 of 248 (12%) controls, Fisher's p (p(f)) = .005. Thrombophilic factor VIII was high in four of 10 (40%) cases vs. 0 of 38 controls, p(f) = .001. Thrombophilic hyperestrogenemia in five of the eight women (four exogenous estrogen, one pregnant) may have interacted with inherited thrombophilia-hypofibrinolysis, promoting thrombus formation. In cases selected by the absence of abnormal brain magnetic resonance imaging, significant ipsilateral internal carotid artery plaque, atrial fibrillation, or cardiac thrombus, we speculate that amaurosis fugax can be caused by reversible (by anticoagulation) retinal artery thrombi associated with heritable thrombophilia and/or hypofibrinolysis, often augmented by estrogen-driven acquired thrombophilia.

M385T polymorphism in the factor V gene, but not Leiden mutation, is associated with placental abruption in Finnish women

This study determines whether genetic variability in the gene encoding factor V contributes to differences in susceptibility to placental abruption. Allele and genotype frequencies of three single nucleotide polymorphisms (SNPs) in the factor V gene leading to nonsynonymous changes (M385T in exon 8, and R485K and R506Q [Leiden mutation] in exon 10) were studied in 116 Caucasian women with placental abruption and 112 healthy controls. Single-point analysis was expanded to haplotype analysis and haplotype frequencies were estimated using an expectation-maximisation (EM) algorithm. Comparison of single-point allele and genotype distributions of SNPs in exon 8 and exon 10 of the factor V gene revealed statistically significant differences in M385T allele (P = 0.021) and genotype ( P = 0.013) frequencies between the patients and the control subjects. The C allele of SNP M385T was significantly less frequent among the patients (7%) vs. the control subjects (13%), at an odds ratio of 0.48 (95% CI 0.25-0.91). Allele and genotype differences between the patients and control subjects as regards R485K and Leiden mutation were not significant. In haplotype estimation analysis, there was a significantly lower frequency of haplotype T-R-R encoding the T385-R485-R506 variant in the group with placental abruption vs. the control group (P = 0.038) at an odds ratio of 0.519 (95% CI 0.272-0.987). We conclude that T385 is less frequent among the patient group than in the control group. The M385T variant in the factor V gene other than the Leiden mutation may play a role in disease susceptibility.

Thrombin generation: phenotypic quantitation

An individual's ability to generate thrombin following tissue factor stimulus was evaluated in 13 healthy male donors in a 6-month study. Thrombin generation in whole blood collected by phlebotomy, contact pathway suppressed by the presence of 100 micro g mL-1 corn trypsin inhibitor, was initiated by the addition of 5 pm tissue factor/10 nm phospholipid. Reactions were quenched at 20 min by the addition of an ethylenediaminetetraacetic acid (EDTA), benzamidine, FPRck cocktail. Thrombin generation was determined by an ELISA for thrombin-antithrombin III (TAT) complex formation. Results showed that the levels of TAT observed varied from 245 to 775 nm. Thrombin production was consistent within each individual, CVi = 11.6%, but varied significantly within the group, CVg = 25.2%, and correlated inversely with an individual's clotting time (r = - 0.54, P = 0.07). No correlations were individually observed between TAT and C-reactive protein, antithrombin III, factors II, V, VII, VIII, IX and X, fibrinogen and prothrombin time. However, computer simulations, which integrated each individual's coagulation factor levels using the Speed Rx method (Hockin et al., J Biol Chem 2002; 277: 18322), predicted maximum active thrombin levels (ranging from calculated values of 220-500 nm) consistent with the empirically determined values. Overall, these data suggest that thrombin generated in whole blood exclusively by tissue factor stimulation can be used as an integrative phenotypic marker to determine an individual's response to a tissue factor challenge.

Hypercoagulability, a serious problem in patients with ESRD on maintenance hemodialysis, and its correction after kidney transplantation

BACKGROUND

Recurrent vascular access thrombosis (VAT) resulting in failure to continue maintenance hemodialysis (HD) therapy is not an uncommon event. The cause of VAT in these circumstances remains uncertain. We describe results of our studies to identify changes in hemostatic balance in patients on maintenance HD therapy that probably contributed to a hypercoagulable state.

METHODS

We studied 82 patients with end-stage renal disease on maintenance HD therapy who underwent HD for 11 to 52 months (39.3 +/- 27.4 months). Forty-nine episodes of VAT occurred in 22 patients; a single episode occurred in 12 patients; and 2 or more episodes, in 10 patients. Blood coagulation studies, including assays of inhibitors and activated protein C (PC) resistance (APCR), were performed using standard techniques.

RESULTS

Investigations showed the presence of lupus anticoagulant (LA) in 5.6%, anticardiolipin antibody immunoglobulin G (IgG) in 3.9% and IgM in 5.3%, APCR in 20.5%, and deficiencies in protein S (PS), PC, and antithrombin III (ATIII) in 32.1%, 24.4%, and 19.2%, respectively. When parameters were compared between patients with and without VAT episodes, LA, PC, PS, and APCR levels were significantly abnormal in those who experienced VAT. Sixteen subjects with hypercoagulable states on HD therapy underwent renal transplantation and were evaluated 9.3 +/- 4.2 months posttransplantation. Deficiencies in PC (P = 0.014), PS (P = 0.001), ATIII (P = 0.017), and APCR (P = 0.0001) were completely corrected in all subjects.

CONCLUSION

Hypercoagulability is a risk factor for recurrent VAT in HD patients, and renal transplantation successfully corrects these abnormalities.

Susceptibility to pre-eclampsia in Finnish women is associated with R485K polymorphism in the factor V gene, not with Leiden mutation

This study determines whether genetic variability in the gene-encoding factor V contributes to differences in pre-eclampsia susceptibility. Allele and genotype frequencies of three single-nucleotide polymorphisms (SNPs) in the factor V gene leading to nonsynonymous changes (M385T in exon 8, and R485K and R506Q (Leiden mutation) in exon 10) were studied in 133 Caucasian women with pre-eclampsia and 112 healthy controls. Single-point analysis was expanded to haplotype analysis, and haplotype frequencies were estimated using an expectation-maximization algorithm. Comparison of single-point allele and genotype distributions of SNPs in exons 8 and 10 of the factor V gene revealed statistically significant differences in R485K allele (P=0.003) and genotype (P=0.03) frequencies between the patients and the control subjects. The A allele of SNP R485K was over-represented among the patients (12%) vs the control subjects (4%), at an odds ratio (OR) of 2.8 (95% confidence interval (CI) 1.2-6.2) for combined A genotypes (GA+AA vs GG). Allele and genotype differences between the patients and control subjects as regards M385T and Leiden mutation were not significant. In haplotype estimation analysis, there was a significantly elevated frequency of haplotype T-A-G encoding the M385-K485-R506 variant in the pre-eclamptic group vs the control group (P=0.01), at an OR of 2.6 (95% CI 1.2-5.5). We conclude that the T-A-G haplotype was more frequent among the patient group than in the control group, and genetic variations in the factor V gene other than the Leiden mutation may play a role in disease susceptibility.