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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. [ABSTRACT FROM AUTHOR]

Thirty per cent of patients with mild haemophilia A (MHA) present markedly different FVIII: C level when assayed by one-stage clotting and two-stage chromogenic assays. It is, therefore, a real clinical challenge to predict the individual bleeding risk of these patients. The aim of the present work was to study the relationship between the bleeding tendency of these patients with the results of a panel of phenotypic and genotypic tools. Thirty-six patients with MHA were included in this multicentre prospective clinical study. The severity of bleeding symptoms was evaluated using the ISTH/SSC score. FVIII:C levels were measured using an activated partial thromboplastin time-based one-stage FVIII assay (FVIII: C1) and three commercial chromogenic kits (FVIII:CR). FVIII antigen levels, thrombin generation measurement and FVIII gene mutation analysis were also performed. Our results showed that a one-stage FVIII: C assay cannot rule out the diagnosis of MHA, a combined use of FVIII:C1 with a FVIII:CR is suitable for detecting MHA. We observed that FVIII:CR results better reflected the clinical bleeding tendency of patients compared to FVIII:C1. We also observed a relationship between thrombin generation (TG) capacity and FVIII:CR of these patients. FVIII gene mutation analysis showed mutations previously reported in MHA patients with discrepant FVIII:C measurements, but with no predictive value of the individual bleeding phenotype of patients. Overall, we observed a relationship between chromogenic FVIII:C results, TG assay and bleeding tendency of patients with discrepant FVIII:C measurements, while FVIII:C1 was not well correlated with clinical bleeding phenotype in this particular population. [ABSTRACT FROM AUTHOR]

Summary. Type 2N von Willebrand's disease (VWD) is characterized by a factor VIII (FVIII) deficiency and a low FVIII/VWF ratio related to a markedly decreased affinity of von Willebrand factor (VWF) to FVIII. Type 2N VWD is diagnosed using assays allowing the measurement of plasma VWF capacity to bind FVIII (VWF:FVIIIB). These assays, crucial in order to distinguish type 2N VWD patients from mild haemophiliacs A and haemophilia A carriers, remain exclusively homemade and limited to laboratories possessing a high level of expertise in VWD. We evaluated the first commercial ELISA (Asserachrom® VWF:FVIIIB; Stago) comparated to a reference method in a multicentric study involving 205 subjects: 60 healthy volunteers, 37 haemophiliacs A, 17 haemophilia A carriers, 37 patients with type 2N VWD, 9 heterozygous carriers for a 2N mutation and 45 patients with miscellaneous other types of VWD (all previously characterized). A diluted plasma sample adjusted to 10 IU dL−1 of VWF:Ag was incubated with a rabbit antihuman VWF polyclonal antibody. After removing the endogenous FVIII, recombinant FVIII (rFVIII) was added and bound rFVIII was quantified using a peroxydase-conjugated mouse antihuman FVIII monoclonal antibody. The intra-assay and inter-assay reproducibility was satisfactory. In all subgroups, both methods were well correlated. All type 2N VWD patients exhibited a markedly decreased VWF:FVIIIB (lower than 15%) and all heterozygous 2N carriers had a moderately decreased VWF:FVIIIB (between 30% and 65%). All controls (healthy subjects, haemophiliacs A and haemophilia A carriers) had a normal VWF:FVIIIB (higher than 80%) except one healthy volunteer and three haemophiliacs who exhibited a moderately decreased VWF:FVIIIB suggesting a heterozygous status for a 2N mutation. In conclusion, the Asserachrom® VWF:FVIIIB is easy to perform, standardized and accurate for type 2N VWD diagnosis with a 100% sensitivity and specificity. [ABSTRACT FROM AUTHOR]