Agreement between factor XIII activity and antigen assays in measurement of factor XIII: A French multicenter study of 147 human plasma samples.

INTRODUCTION: Factor XIII (FXIII) deficiency is a rare hemorrhagic disorder whose early diagnosis is crucial for appropriate treatment and prophylactic supplementation in cases of severe deficiency. International guidelines recommend a quantitative FXIII activity assay as first-line screening test. FXIII antigen measurement may be performed to establish the subtype of FXIII deficiency (FXIIID) when activity is decreased. METHODS: The aim of this multicenter study was to evaluate the analytical and diagnostic levels of performance of a new latex immunoassay, K-Assay® FXIII reagent from Stago, for first-line measurement of FXIII antigen. Results were compared to those obtained with the Berichrom® FXIII chromogenic assay for measurement of FXIII activity. Of the 147 patient plasma samples, 138 were selected for analysis. RESULTS: The accuracy was very good, with intercenter reproducibility close to 7%. Five groups were defined on FXIII activity level (<5% (n = 5), 5%-30% (n = 23), 30%-60% (n = 17), 60%-120% (n = 69), above 120% (n = 24)), without statistical differences between activity and antigen levels (P value >0.05). Correlation of the K-Assay® with the Berichrom® FXIII activity results was excellent (r = 0.919). Good agreement was established by the Bland and Altman method, with a bias of +9.4% on all samples, and of -1.4% for FXIII levels lower than 30%. One patient with afibrinogenemia showed low levels of Berichrom® FXIII activity but normal antigen level and clot solubility as expected. CONCLUSIONS: The measurement of FXIII antigen using the K-Assay® is a reliable first-line tool for detection of FXIII deficiency when an activity assay is not available.

Does the presence of von Willebrand factor in FVIII-deficient plasma influences the measurement of FVIII inhibitor titres in haemophilia A patients?

INTRODUCTION: Reliable measurement of FVIII inhibitor is critical in the follow-up of haemophilia A patients. We performed a multicentre study to evaluate whether the presence of von Willebrand factor (VWF) in FVIII-deficient plasma (FVIII-DP) influences FVIII inhibitor titres. METHODS: Six French haematology laboratories participated in this study. Three samples with varying FVIII inhibitor titres (1, 5 and 15 BU/mL) and one sample without any detectable FVIII inhibitor were tested using four different procedures for FVIII inhibitor assay. The Nijmegen method and a modified assay with imidazole were performed using FVIII-DP with and without VWF in the control mixture and as substrate plasma in the FVIII one stage assay (OSA). Each mixture (reference and test) was incubated for two hours at 37 °C with buffered normal pool plasma. RESULTS: Higher inhibitor titres were measured in 5 and 15 BU/mL samples when assays were performed with the Nijmegen method and FVIII-DP without VWF. When samples were diluted in imidazole buffer, similar inhibitor titres, close to expected values, were measured whether VWF was present in the FVIII-DP or not. The data obtained were also more accurate when residual FVIII activity levels between 40% and 60% were used to calculate inhibitor titres, despite a linear type I reaction kinetics. CONCLUSION: These results support the hypothesis that reliable FVIII inhibitor titres can be measured without the use of FVIII-DP containing VWF when an imidazole-modified assay is used.

Risk assessment of venous thrombosis in families with known hereditary thrombophilia: the MARseilles-NImes prediction model.

BACKGROUND: Although predicting the risk of venous thrombosis (VT) in an individual from a family with inherited thrombophilia is of major importance, it is often not feasible. OBJECTIVES: To develop a simple risk assessment model that improves prediction of the risk of VT for individuals of families with inherited thrombophilia. PATIENTS/METHODS: 1201 relatives from 430 families with inherited thrombophilia (deficiencies of antithrombin, protein C or protein S, and the factor V Leiden and F2 20210A mutations) were recruited at the referral center for thrombophilia in Marseilles, France, from 1986 to 2008. One hundred and twenty-two individuals had a personal history of VT. Sixteen preselected clinical and laboratory variables were used to derive the VT risk score. RESULTS: The scores based on the 16 variables and on the five most strongly associated variables performed similarly (areas under receiver operating characteristic curves of 0.85 and 0.83, respectively). For the five-variable score, named the MARNI score, derived from family history score of VT, von Willebrand factor antigen levels, age, severity of thrombophilia, and FGG rs2066865, the risk of VT ranged from 0.2% for individuals with a score of 0 (n = 186) to > 70% for individuals with a score of ≥ 7 (n = 27). The model was validated with an internal bootstrap method. CONCLUSIONS: With the use of a simple scoring system, assessment of the risk of VT in subjects from families with inherited thrombophilia can be greatly improved. External validation is now needed to replicate these findings.

Risk assessment of venous thrombosis in families with known hereditary thrombophilia: the MARseilles-NImes prediction model.

BACKGROUND: Although predicting the risk of venous thrombosis (VT) in an individual from a family with inherited thrombophilia is of major importance, it is often not feasible. OBJECTIVES: To develop a simple risk assessment model that improves prediction of the risk of VT for individuals of families with inherited thrombophilia. PATIENTS/METHODS: 1201 relatives from 430 families with inherited thrombophilia (deficiencies of antithrombin, protein C or protein S, and the factor V Leiden and F2 20210A mutations) were recruited at the referral center for thrombophilia in Marseilles, France, from 1986 to 2008. One hundred and twenty-two individuals had a personal history of VT. Sixteen preselected clinical and laboratory variables were used to derive the VT risk score. RESULTS: The scores based on the 16 variables and on the five most strongly associated variables performed similarly (areas under receiver operating characteristic curves of 0.85 and 0.83, respectively). For the five-variable score, named the MARNI score, derived from family history score of VT, von Willebrand factor antigen levels, age, severity of thrombophilia, and FGG rs2066865, the risk of VT ranged from 0.2% for individuals with a score of 0 (n = 186) to > 70% for individuals with a score of ≥ 7 (n = 27). The model was validated with an internal bootstrap method. CONCLUSIONS: With the use of a simple scoring system, assessment of the risk of VT in subjects from families with inherited thrombophilia can be greatly improved. External validation is now needed to replicate these findings.

The use of the new ReFacto AF Laboratory Standard allows reliable measurement of FVIII:C levels in ReFacto AF mock plasma samples by a one-stage clotting assay.

Factor VIII coagulant (FVIII:C) levels measured in patients receiving ReFacto® (B-domain-deleted recombinant FVIII) using chromogenic substrate assay (CSA) and one-stage clotting assay (OSA) have frequently shown discrepancies, and the use of the ReFacto Laboratory Standard (RLS) has therefore been recommended to minimize these differences. The potency of ReFacto AF®, the albumin-free successor of ReFacto®, is determined using CSA for the titration of vials, and a new standard (RLS-AF) was developed to measure its biological efficacy using OSA. This multicentre study therefore evaluated the efficacy of this new RLS in minimizing differences between OSA and CSA when measuring FVIII:C levels in plasma. Mock plasma samples were prepared by diluting ReFacto AF® in FVIII-deficient plasma to obtain four concentrations ranging from 15 to 90 IU dL⁻¹ . FVIII:C levels were then measured in six laboratories on four separate days using three different procedures, i.e. OSA with a plasma standard (PS) as reference, OSA with RLS-AF and CSA with PS. The inter-centre standard deviation ranged from 1.4 to 5.5 IU dL⁻¹. However, FVIII:C levels measured with OSA were closer to the expected values when RLS-AF was used. In addition, the uncertainty of measurement, reflecting the inter-method discrepancy was greatly reduced when RLS-AF was employed in OSA (15%) in place of PS (33%). This study demonstrates that the OSA performed with RLS-AF to establish calibration curves provides a valuable alternative to CSA to measure FVIII:C in ReFacto-AF-treated patients.

Effect of Interleukin-6 promoter polymorphisms in survivors of myocardial infarction and matched controls in the North and South of Europe. The HIFMECH Study.

Elevated plasma IL-6 levels have been implicated in the pathogenesis of coronary heart disease. We have investigated the association of two polymorphisms in the promoter of IL-6 (-572G>C and -174G>C) with levels of inflammatory markers and risk of myocardial infarction (MI) in a European study of MI survivors and age-matched controls from two high-risk centres in the North of Europe, and two low risk centres in the South. IL-6 and CRP levels were similar in controls in both regions, but were higher in cases. For the -174G>C polymorphism the rare -174C allele showed a regional difference in allele frequency, being more common in the North European group (0.43 vs 0.28; p < 0.0005), where -174C allele carriers showed an apparent reduced risk of MI compared to -174GG homozygotes (OR 0.53, 95%CI 0.32, 0.86). No such effect was observed in the South or with the -572G>C in either group. Neither genotype was associated with a significant effect on plasma IL-6 levels in either cases or controls. Furthermore, no regional difference was observed in the frequency of the -572G>C SNP, suggesting that these polymorphisms are unlikely to be contributing to the observed increased risk of cardiovascular disease in Northern Europe.

The plasminogen activator inhibitor-1 -675 4G/5G genotype influences the risk of myocardial infarction associated with elevated plasma proinsulin and insulin concentrations in men from Europe: the HIFMECH study.

UNLABELLED: Although the potential role of plasminogen activator inhibitor-1 (PAI-1) in the development of coronary artery disease is strongly supported by its biological characteristics, results of clinical studies remain controversial. OBJECTIVES: To investigate whether plasma PAI-1 concentrations and the -675 4G/5G polymorphism located in the PAI-1 gene could constitute risk markers for myocardial infarction (MI). PATIENTS AND METHODS: We used a European case-control study, the HIFMECH study, comparing 598 men with MI and 653 age-matched controls. RESULTS: Insulin resistance explained a major part of the variation in PAI-1 (24%) whereas inflammation had only a minor contribution (0.01%). For both cases and controls plasma PAI-1 concentrations were significantly higher in the North than the South, and in both regions were higher in individuals with MI compared with control subjects [overall odds ratio (OR) for a 1 SD increase=1.54, 95% confidence interval (CI) 1.34, 1.77]. This difference was observed in all the centers studied. Overall, the difference between cases and control subjects remained significant after controlling for inflammation variables (OR=1.30, 95% CI 1.08, 1.57), but lost significance after controlling for insulin resistance variables (OR=1.17, 95% CI 0.98, 1.40). The 4G allele was associated with significantly higher PAI-1 levels in cases but not controls and, taken independently, did not modify the risk of MI (P=0.9). However, a significant interaction was observed with both insulin or proinsulin and the risk of MI (P=0.05 and 0.02, respectively), but not with triglycerides or body mass index (BMI). The insulin or proinsulin effect on risk was observed only in the carriers of the 4G/4G genotype. This interaction appeared not to be mediated by plasma PAI-1 antigen concentrations (P=0.01 and 0.02 after adjustment for PAI-1 plasma levels). The interaction with proinsulin but not insulin remained statistically significant after further adjustment for other factors associated with insulin resistance (triglycerides and BMI) and C-reactive protein (P=0.01). CONCLUSION: This study suggests that PAI-1 has a role in risk of MI in the presence of underlying insulin resistance. A significant interaction between insulin or proinsulin and the -675 4G/5G polymorphism was observed in risk for MI. The mechanisms for these interactions remain to be determined.

Weak and non-independent association between plasma TAFI antigen levels and the insulin resistance syndrome.

Increased plasma thrombin-activatable fibrinolysis inhibitor (TAFI) levels were recently shown to be a part of the insulin resistance syndrome. We investigated the relationship between plasma TAFI antigen levels and insulin resistance markers and compared these results with those obtained for PAI-1 and fibrinogen which are known to be closely related to insulin resistance syndrome and fat mass, respectively. Eighty-nine obese females had 1.3-, 1.2-, and 3-fold higher circulating TAFI, fibrinogen and PAI-1, respectively, compared with 64 lean females. Univariate analysis showed that the significance level for association between TAFI or fibrinogen concentrations and insulin resistance markers was lower than the significance level for association between PAI-1 and insulin resistance markers. Nevertheless, TAFI, fibrinogen, and PAI-1 plasma levels were significantly associated to each other. In linear stepwise ascendant analysis, insulin resistance markers accounted for 50% of the interindividual variability of plasma PAI-1 and only for 10% of plasma TAFI and 13% of fibrinogen variability. The contribution of insulin resistance markers to plasma TAFI antigen levels variability disappeared when PAI-1 or fibrinogen was entered in the statistical model. TAFI mRNA was detected in the liver but not in adipose tissue and endothelial cells. No TAFI mRNA was detected in normal or atherosclerotic vessels either. These results suggest that elevated TAFI antigen levels found in obese subjects are not independently associated with the metabolic markers of the insulin resistance syndrome. Increased plasma TAFI antigen levels in obesity might reflect a specific pathway of regulation at the liver level.

Plasma thrombin-activatable fibrinolysis inhibitor antigen concentration and genotype in relation to myocardial infarction in the north and south of Europe.

The thrombin-activatable fibrinolysis inhibitor (TAFI) is a recently described inhibitor of fibrinolysis that decreases plasminogen binding to the fibrin surface. The plasma TAFI concentration is almost entirely genetically determined. We investigated whether plasma TAFI levels and polymorphisms located in the TAFI gene could constitute risk markers of myocardial infarction (MI). Plasma TAFI antigen (Ag) levels were assayed by ELISA and 2 TAFI gene polymorphisms (Ala147Thr and C+1542G in the 3' untranslated region) were determined in a large European case-control study. This study compared 598 men recruited 3 to 6 months after MI with 653 age-matched controls from North Europe (Stockholm, Sweden, and London, England) and South Europe (Marseilles, France, and San Giovanni Rotondo, Italy). A TAFI Ag value above the 90th percentile was associated with a significantly lower risk of MI (odds ratio 0.55, P<0.02), indicating that elevated TAFI may be protective against MI. As previously shown, the 2 TAFI gene polymorphisms were in strong linkage disequilibrium and were associated with the TAFI Ag concentration, with carriers of the Thr147 and 1542C alleles having higher levels (P<0.0005). These effects were similar in controls and cases and in each center. There was a difference in allele frequency between cases and controls for the Ala147Thr polymorphism, with Thr147 allele carriers being more frequent in controls than in cases in 2 centers, Stockholm (P=0.03) and San Giovanni Rotondo (P=0.03); the odds ratio for the entire cohort was 0.78 (P<0.05). In conclusion, patients with a recent MI presented lower values of TAFI Ag and higher frequencies of the "TAFI-decreasing" alleles. The geographical differences observed do not contribute to explaining the North-South gradient in MI risk in Europe.

The clinical relevance of the citrate effect on International Normalized Ratio determinations depends on the reagent and instrument combination used.

Multiple studies have shown that the two different citrate concentrations in common use as the anticoagulant in blood collection for haemostasis assays can affect the results obtained with the prothrombin time assay. It is clear from the literature that there is considerable variability in the results obtained using different instrument-reagents combinations, but the clinical relevance of these differences is unclear. Most of the studies have used an optical system for end-point detection. This study reports on the citrate sensitivity using mechanical end-point detection. Using two different reagents, one previously shown to be citrate sensitive on optical systems (Neoplastin CI plus) and a citrate-insensitive reagent (Neoplastin CI), we demonstrate that the effect of using different citrate concentrations (0.105 or 0.129 mol/l) has statistically significant but clinically irrelevant effects on the International Normalized Ratio using a mechanical instrument (STA)-reagent combination (mean percentage difference in results, 1.9 and 3.8% respectively). This demonstrates that the citrate effect is both instrument type and reagent dependent. Every reagent and instrument combination needs to be tested to see whether any citrate effect exists. In a secondary study, it was shown that the international reference rabbit thromboplastin (CRM 149(s)) was not citrate-concentration sensitive.

Plasma levels of free and total TFPI, relationship with cardiovascular risk factors and endothelial cell markers.

Free-TFPI (f-TFPI) presents high anticoagulant activity and its plasma level correlates with unfavorable outcomes in unstable angina. Total TFPI (t-TFPI) represents mainly the lipid-bound form which seems to have a poor anticoagulant activity. Until now, it is not known whether the variations of f-TFPI plasma levels are determined by environmental factors. The aim of our study was to evaluate the influence of cardiovascular risk factors on plasma levels of f-TFPI and relations with other endothelial derived molecules in a population of 626 patients (277 men and 349 women) attending a metabolic ward for primary prevention of coronary disease. Free and total TFPI plasma levels were poorly correlated. f-TFPI levels increased with age in both sexes, t-TFPI in women only. Age-adjusted correlations of TFPI levels with conventional cardiovascular risk factors and endothelial cell markers showed different patterns for f-TFPI and t-TFPI. f-TFPI correlated with parameters associated with insulin resistance, particularly in females. f-TFPI was also positively associated in both genders with fibrinogen and endothelial cell markers: t-PA, thrombomodulin (TM) and von Willebrand factor (vWF). t-TFPI correlated strongly with LDL-C in both sexes. It also correlated negatively with parameters of the insulin resistance syndrome. t-TFPI also correlated with TM but not with other endothelial cell markers. The results of the multivariate step by step analysis showed that cardiovascular risk factors poorly explained the f-TFPI variability (7% and 4% in men and women, respectively), whereas they explained 16 and 20% of t-TFPI variability in men and women respectively (mostly related to LDL-C). In conclusion, this study showed that free- and total-TFPI are regulated differently. f-TFPI strongly correlates with endothelial cell markers and t-TFPI is more related to conventional cardiovascular risk factors. The strong gender effect on f-TFPI levels remains to be explained.

Antibodies to phosphatidylethanolamine as the only antiphospholipid antibodies found in patients with unexplained thromboses.

The objective of this study was to assess the interest of antiphosphatidylethanolamine antibodies (aPE) in unexplained thrombosis (UT) defined as thrombotic episode without any of the main autoimmune and hereditary thrombophilic defects. Results from 98 UT were compared to those of (I) 142 patients with thrombophilia: 67 antiphospholipid syndrome (APS) and 75 hereditary hemostatic defects (HHD); (II) 110 patients without thrombosis: 60 with systemic lupus erythematosus (SLE) and 50 with infectious diseases (ID). As compared to controls (100 blood donors), aPE prevalence was significantly higher in both autoimmune contexts (APS: 43%; SLE: 40%, p<0.0001) and among non-autoimmune pathologies, only in UT (18%, p = 0.001) conversely to HHD (8%) or ID (10%). aPE prevalence in UT was not statistically different from that found in Primary APS (32%, p = 0.076) but lower than in Secondary APS (65%, p <0.005). In UT, aPE were mainly of IgM isotype like in Primary APS and they were found alone whereas in SLE they were always associated with classical antiphospholipid antibodies. No significant association was found between any isotype of aPE and a site of thrombosis in UT as well as in APS. In conclusion, this study demonstrates an increase of the prevalence of aPE in patients with unexplained thrombosis. Thus, aPE investigation appears to be of interest in UT and their persistent presence could define a biological variant of APS.

Haemostasis in relation to dietary fat as estimated by erythrocyte fatty acid composition: the prime study.

We investigated whether haemostatic variables were related with dietary fatty acid composition as estimated by the fatty acid content of erythrocytes. Subjects were a subsample (n=283) of the participants in the Prospective Epidemiological Study of Myocardial Infarction (PRIME) Study. Factor VII, fibrinogen, tissue-type plasminogen activator antigen (tPA-ag), plasminogen activator inhibitor type 1 (PAI-1), D-dimer and von Willebrand factor (vWf) were measured and the fatty acid composition was determined in the phospholipids of total erythrocytes by gas chromatography. Statistical analyses were performed using multiple linear regression analyses with adjustment for age, center and body mass index. tPA-ag was significantly related to the n-3 fatty acids derived from fish. This was reflected in an inverse association of all n-3 fatty acids combined with tPA-ag (beta=-0.37 ng/ml/%, 95% confidence intervals: -0.45, -0.29, P<.01). Positive and significant associations of D-dimer with arachidic and eicosamonoenoic acid were observed (P<.01). No relationships were found between fatty acids and fibrinogen, vWf, PAI-1 or factor VII. The results of this study suggest that consumption of n-3 fatty acids derived from fish may favourably influence tPA-ag.

The A -844G polymorphism in the PAI-1 gene is associated with a higher risk of venous thrombosis in factor V Leiden carriers.

Identification of combined genetic factors in factor V Leiden carriers is important for a more accurate risk assessment for venous thrombosis (VT). Among these individuals, we evaluated the role of polymorphisms of the plasminogen activator inhibitor-1 (PAI-1) gene in the thrombophilic phenotype. A total of 382 factor V Leiden carriers were included in the study. This population was divided into 3 groups. Group 1 (n=168) included individuals with a personal history of VT; group 2 (n=140) included individuals without personal VT but with a familial history of VT; and group 3 (n=74) included individuals without VT and with a fortuitous discovery of the factor V Leiden mutation. We compared the genotype distribution of 2 polymorphisms, A -844G and -675 4G/5G, located in the promoter region of the PAI-1 gene among these 3 groups of individuals. The A -844G allele frequency differed significantly among the 3 groups (P=0.048), the A allele being more frequent in patients who suffered from VT (61%) than in subjects without VT (52%, P=0.015), whereas no difference was observed between the 2 groups of asymptomatic individuals. The prevalence of genotype AA carriers was higher in patients with VT (38%) than in asymptomatic individuals (21%, P=0. 015), leading to an odds ratio of 1.74 (95% confidence interval, 1.3 to 3.8). Carrying the AA genotype conferred a risk of deep VT of 2. 08 (95% confidence interval, 1.28 to 3.40), whereas it did not seem to significantly influence the risk of pulmonary embolism. Concerning the -675 4G/5G polymorphism, no significant difference was observed among the 3 groups, the 4G allele frequency being 0.54 (in group 1), 0.49 (in group 2), and 0.45 (in group 3). These data suggest a role for the -A844G PAI-1 gene polymorphism in the thrombophilic phenotype of factor V Leiden carriers.