SummaryTo assess variations of coagulation factors in women, 123 women were included in a cross-sectional study of the effect of age, ethnic origin, blood group and menstrual cycle on surface induced coagulation time (activated partial thromboplastin time) and plasma levels of Factor VIII clotting assay, von Willebrand factor antigen, von Willebrand factor activity and factor XI. The effect of menstrual cycle was further assessed in a longitudinal study including 39 Caucasian women, 20 of whom were using combined oral contraceptives. Activated partial thromboplastin time was longer in women with blood groups B or O, and plasma levels of factor VIII clotting assay, von Willebrand factor antigen and von Willebrand factor activity were significantly higher in black women. Fibrinogen, von Willebrand factor antigen and von Willebrand factor activity concentrations showed strong cyclic variations with peak values in the luteal phase. This pattern was dampened for von Willebrand factor antigen and von Willebrand factor activity but completely disappeared for fibrinogen with the use of combined oral contraceptives. There was a cyclical pattern for factor VIII clotting assay in pill users, evidence of which was not evident in non-pill users. There were strong associations between the levels of von Willebrand factor antigen and von Willebrand factor activity and age, with levels rising by an average of 0.17 and 0.15 U/ml, respectively, for each 10 year increase in age. In conclusion, there are great inter- and intraindividual variations in coagulation markers in women due to different physiological conditions such as age, ethnicity, blood group and phases of the menstrual cycle. However, there were no significant associations between coagulation markers and weight, alcohol consumption or smoking status.
SummaryIn order to investigate the possibility that qualitative type 2 defects in von Willebrand factor (VWF) occurred in patients previously diagnosed with quantitative type 1 von Willebrand disease (VWD), the phenotypes and genotypes were reanalysed in 30 patients who exhibited discrepant VWF activity/VWF:Ag ratios of less than 0.7. The capacity of VWF to bind to glycoprotein Ib (GpIb) was reassessed using the ristocetin co-factor activity (VWF:RiCo) assay compared to an in-house and a commercial ELISA assay (based on a mAb directed against the GpIb binding site on VWF). This was supplemented by multimeric analysis and the amplification and sequencing of a 936 bp fragment of exon 28 of the VWF gene with the aim of identifying mutations in the A1 domain. On reappraisal, using the VWF:RiCo assay all patients demonstrated a disproportionately reduced VWF:RiCo/VWF:Ag ratio, indicative of a qualitative defect, while abnormal ratios were detected in only seven kindreds using the in-house ELISA assay and in only one kindred with the commercial ELISA assay. Eight single amino acid substitutions were found in nine kindreds, four of which were novel candidate VWF mutations and four previously described in association with type 2 VWD. In agreement with the phenotype, the novel VWF mutations were located in the VWF-A1 crystal structure at positions that corresponded to potential type 2M defects. This study underlines the difficulties of correct diagnosis of the subtype of VWD and emphasises the importance of using sensitive phenotypic assays, the relevance of the VWF:RiCo/ VWF:Ag ratio, multimeric analysis and molecular modelling analysis.
Summary. It has been well documented that there is an uncertainty over the true factor (F)VIII level in postinfusion samples due to assay discrepancies. The thrombin generation test (TGT) was used as a potentially more physiological approach to assess and compare FVIII concentrates. FVIII concentrates were added to artificial FVIII-deficient plasma. Thrombin generation was initiated by the addition of FIXa (14 nM), phospholipid and CaCl 2 . Thrombin was measured by subsampling into fibrinogen, and curves quantified as area under the curve (AUC) and time taken to half-maximum (t ½max ). Addition of one plasma-derived concentrate to as little as 0.005 IU mL À1 gave a normal AUC, but prolonged t ½max . Increasing FVIII to 1 IU mL À1 had little effect on AUC, but did reduce the t ½max to 64 s (normal 114 s). A range of plasmaderived and recombinant concentrates were tested at 1 IU mL À1 ; results were similar, except the B-domain deleted concentrate, which had the most rapid initial rate of thrombin generation (t ½max 48 s, P < 0.05). Two hemophilic plasmas (< 0.01 IU mL À1 ) produced large amounts of thrombin (AUC 65% and 69%), although t ½max was prolonged. Addition of a FVIII antibody abolished thrombin generation, indicating that these plasmas contained low levels of FVIII. Decreasing the FIXa concentration (0.2 nM) minimized thrombin generation in hemophilic plasma but not in normal plasma. These results indicate that FVIII <0.01 IU mL À1 can generate significant quantities of thrombin depending upon the amount of FIXa present. The TGT could prove useful for patient monitoring in gene therapy and prophylaxis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.