Catálogo de publicaciones - libros

For daily laboratory routine work the one-stage clotting assay can be adapted to most indications. For diagnosis of severe hemophilia FVIII levels below 1% can be assessed by a separate calibration. For therapy monitoring and measurement of concentrates ISTH-SCC recommendations should be followed. Measuring »like vs. like« (optimal: assay calibration with concentrate standard the same as the infused concentrate) eliminates the major differences between assay methods. In diagnosis of thrombophilia FVIII levels above and below 150% can be easily differentiated. Chromogenic assays might be of special use in labeling of B-domain-deleted recombinant concentrates. However, basic causes of the observed assay differences remain (partly) unknown.

It can be concluded that in general factor VIII inhibitor testing showed a large between- laboratory variability. The results of the users of the Nijmegen modified assay are more comparable than those of the users of the classical Bethesda assay. Furthermore, testing of factor VIII inhibitors needs further standardization and improvement of the sensitivity and specificity.

Total of 5649 unselected adult patients were enrolled to identify impaired hemostasis prior to surgical interventions. Each patient was asked to answer a standardized questionnaire of bleeding history. Activated partial thromboplastin time (aPTT), prothrombin time (PT) and platelet counts (PC) including PFA-100 (platelet function analyzer): collagen-epinephrine (C/E) and collagen-ADP (C/ADP) were routinely done in all patients. Additional tests, bleeding time (BT) and von Willebrand factor (vWF: Ag) were performed only in patients with a positive bleeding history and/or evidence of impaired hemostasis, e.g. drug ingestion. The bleeding history was negative in 5021 patients (88.8%) but positive in the remaining 628 (11.2%). Impaired hemostasis could be verified only in 256 (40.8%) of these patients. The vast majority were identified by PFA-100: C/E (n = 250; 97.7%). The only abnormality found among patients with a negative bleeding history was a prolonged aPTT due to lupus anticoagulant in 9 patients (0.2%). The sensitivity of the PFA-100: collagen-epinephrine was the highest (90.8%) in comparison to the other screening tests (BT, aPTT, PT, vWF: Ag). The positive predictive value of the PFA-100: collagen-epinephrine was high (81.8%), but the negative predictive value was higher (93.4%).We identified 254 out of 5649 unselected patients scheduled for surgery at our hospital as having either acquired (n = 182) or inherited (n = 72) impaired primary hemostasis (platelet dysfunction including von Willebrand disease). All patients were initially pretreated with desmopressin (DDAVP) and further anti-bleeding drugs in case of DDAVP-non-response. Response to DDAVP or subsequent treatment(s) was defined as correction of any one of the abnormal PFA-100 platelet function tests. The non-responders were additionally treated with tranexamic acid or aprotinin; those with von Willebrand disease (vWD) received factor VIII concentrates with von Willebrand factor (vWF). Those still unresponsive to therapy received conjugated estrogens and, as a last attempt, a platelet transfusion. The administration of DDAVP led to a correction of platelet dysfunction in 229 of the 254 patients treated (90.2%). Tranexamic acid was effective in 12 of 16, aprotinin in 3 of 5 and factor VIII concentrates with vWF in all 4 patients with unresponsive to DDAVP. The remaining 6 patients were pretreated with conjugated estrogens, and 2 of these patients were additionally treated with platelet transfusion. The frequency of blood transfusion was lower, but not statistically significant (9.4% vs. 12.2%: p = 0.202) in preoperatively treated patients with impaired hemostasis than in patients without impaired hemostasis. In a retrospective group, the frequency of blood transfusion was statistically significant higher (89.3% vs. 11.3%: p < 0.001) in patients without preoperative correction of impaired than in patients without impaired hemostasis. Preoperative identification and correction of impaired primary hemostasis is possible in nearly all patients affected, and results in a reduction of homologous blood transfusions.

The aim of this presentation is to introduce the working-group of the German hemophilia assistants to the hemophilia community. After a first initiative twenty years ago the German hemophilia assistants began to organize themselves as an working-group in 2001. Since then the group met twice a year to discuss special problems of hemophilia care, to define possible contents of a planned qualification program and to have an educational part with a coagulation specific subject. The goal is to define and to guarantee in parallel to the optimal medical treatment also an optimal care for patients with coagulation disorders.

Monitoring of the peri-operatively applied substitution therapy using medication containing factor VIII is feasible by analyzing the endogenous thrombin potential. Compared to the determination of singular parameters a better prediction of the individual coagulation behavior of patients suffering from hemophilia A and von Willebrand Jürgens syndrome (type 3) can be expected. Particularly the postoperative tendency to bleeding is further influenced by products actively supporting coagulation (acute phase proteins).

Acquired hemophilia A is caused by inhibitory autoantibodies to factor VIII (FVIII). Inhibitors block interaction of FVIII and its interacting molecules including factor IX or von Willebrand factor. In acquired hemophilia the knowledge on inhibitor epitopes is limited. Epitopes that have been located so far cluster in the A2 or in the C2 domain of FVIII. In this study plasma samples of patients with FVIII inhibitors have been screened with phage displayed random peptide libraries to identify small peptides that specifically bind to FVIII inhibitors and to locate corresponding epitopes on the surface of FVIII. Screening strategies have been established that allow the isolation of peptides specific for FVIII inhibitors while depleting peptides binding to irrelevant antibodies using whole plasma samples. Specificity of peptide sequences has been demonstrated by various binding assays. The isolated peptides comprising seven to twelve amino acids have been compared to the surface of a FVIII model to identify possible epitopes. Following this approach, epitopes in the A2 or C2 domain were identified for the patients studied.Additional assays are performed to further characterize the epitopes. Currently further samples are being analyzed to identify immunodominant regions in acquired hemophilia, to better understand anti-FVIII-inhibitors in acquired hemophilia and to compare the immune response to congenital hemophilia A.