Recent advances in hemophilia

Classical sex-linked hemophilia (Hemophilia A) has been described as due to deficiency in the synthesis of Factor VIII procoagulant activity (VIII:C). The availability of immunological techniques provided the means of identifying Factor VIII-Related Antigen(VI-IIR:Ag) detectable by rabbit antibodies to F VIII, which is distinct from VIII:C detected by human anti-F VIII available from multitransfused patients. Hemophilia A is lacking in VIII:C but not VIIIR:Ag. Recently, a third function of the F VIII "complex" was discovered with the help of ristocetin (von Willebrand's Factor, VIIIR: RCo). This activity is reduced in von Willebrand's syndrome. Estimation of the titers of VIII:C and VIIIR:Ag provides a method for more accurate detection of hemophilic carriers. Newly available chromogenic substrates perhaps will give rise to more simplified assays of VIII:C. The development of cryoprecipitates and stable lyophilized concentrates of F VIII has greatly simplified and intensified maintenance therapy, and has opened a new era in treatment. Prophylactic therapy has been shown to be very helpful in certain "high risk" cases. The impact and benefits of home care and self-administration has been tremendous. However, the varying quality of cryoprecipitates and the high cost of more purified concentrates are still stumbling blocks in treatment regimes. Other problems exist. Spontaneous bleeding, especially central nervous system bleeding, account for the majority deaths by haemorrhage. Inhibitor kinetics have been well characterized. It is clear that there exists "low" and "high" responders. For the "high" responders, plasmapheresis, immunosuppressives and the infusion of Factor IX concentrates have been utilized with varying success. The prevention of hemophilic arthropathy and its progression by maintenance therapy seems to be still inadequate. The results of trials with more vigorous regimes are awaited. The complications of therapy still remain to be solved. Apart from the well-known complications wuch as hepatitis, haemolytic disease and F VIII inhibitors, the existence of previously unnoticed complications as splenomegaly, hypertension, renal disease and paradoxal bleeding have been recently realized. The role of altered fibrinogen, fibrin degradation products (FDP) and unclassified fibrinogen derivatives (UFD) present in cryoprecipitates and F VIII concentrates in the above complications needs to be further clarified. In conclusion, tremendous progress in various aspects of hemophilia has been achieved in developed countries. Comprehensive care can now be carried out in various centers. On the other hand, developing countries still face a number of basic problems. The concept that hemophilia is a "manageable" disease and that chronic crippling and death from exsanguination can be prevented, should be disseminated widely by various means...     

Acquired von Willebrand's disease in association with Wilm's tumor: regression following treatment

A 9-yr-old female presented with a Wilm's tumor and a coagulopathy consistent with von Willebrand's disease. Factor VIII procoagulant activity (VIII C), factor VIII related antigen (VIIIR:Ag), and von Willebrand factor activity (VIII:vWf) were decreased. There was no evidence for a circulating inhibitor of the factor VIII molecular complex. von Willebrand's antigen II (vW AgII), which is deficient in hereditary von Willebrand's disease, was decreased below detectable levels in this patient. The coagulation studies, VIIIR:Ag, and vW AgII levels returned to normal following therapy of the Wilm's tumor. Wilm's tumor must be included as one of the malignancies associated with acquired von Willebrand's disease. Immunofluorescent studies of the tumor specimen showed normal endothelial staining of VIIIR:Ag by semiquantitative techniques and a lack of specific tumor adsorption of VIIIR:Ag The presence of normal amounts of tissue VIIIR:Ag has not previously been demonstrated in acquired von Willebrand's disease. Since we failed to demonstrate an inhibitor in the plasma in this patient, the etiology of the acquired von Willebrand's disease in this patient appears to differ from other cases of acquired von Willebrand's disease. The finding that vW AgII is decreased in this patient, similar to that reported in hereditary von Willebrand's disease, supports the close association of vW AgII to VIIIR:Ag, even though they are immunologically and biochemically distinct.     

Distribution of plasma fibronectin (cold-insoluble globulin) and components of the factor VIII complex after heparin-induced precipitation of plasma

Factor VIII procoagulant (VIII:C) activity, factor VIII coagulant antigen (VIII:CAg), von Willebrand ristocetin cofactor (VIIIR:RC) activity, factor VIII-related antigen (VIIIR:Ag), and plasma fibronectin (CIg; cold-insoluble globulin) were measured in the heparin precipitable fraction (HPF) and heparin supernatant fraction (HS) of normal human plasma. Following heparin induced precipitation, most measurable VIII:C activity (77% +/- 24%) was recovered in the HS. Although there was little VIII:C activity (less than 1%) in the HPF, 20% +/- 6.5% VIII:CAg was present as well as CIg (81% +/- 5.6%). VIIIR:RC activity (72% +/- 12%), and VIIIR:Ag (34 +/- 5.2%). As assessed by Na dodecyl SO4 glyoxyl agarose electrophoresis, the multimeric forms of plasma VIIIR:Ag could be resolved into a series of bands. Larger multimers tended to precipitate with the HPF whereas the smaller multimers tended to remain supernatant. Plasma from a subject with congenital afibrinogenemia was also studied. Although the afibrinogenemic HPF contained CIg, neither VIIIR:RC activity nor VIIIR:Ag was precipitated. However, both were present in the HPF from afibrinogenemic plasma to which fibrinogen had been added, suggesting that they are incorporated in this precipitate because of an affinity for fibrinogen. The ability of heparin to induce precipitation of CIg while leaving most VIII:C activity in the supernatant plasma may be useful in the preparation of procoagulant-rich plasma subfractions, since VIII:C can subsequently be recovered in good yield by cryoprecipitation.     

Characteristics of the Factor VIII Protein and Factor XIII in Various Factor VIII Concentrates

The in vitro properties of 5 factor VIII preparations (AHF-Kabi, Hemofil Hyland, AHF-Profilate Abbott, Kryobulin Immuno and Factorate High Purity Armour) and an ordinary cryoprecipitate were studied with reference to factor VIII clotting activity (VIII:C), factor VIII clotting antigen (VIILCAg), factor VIII related antigen (VIIIR:Ag) (EI, IRMA, CIE), ristocetin cofactor activity (VIIIR:RCF), fibrinogen and factor XIII. All the preparations with the exception of Factorate had higher levels of VIII:CAg than VIII:C indicating inactivation of the biological activity of VIII:C during the procedure. AHF-Kabi (fraction I-0) and the cryoprecipitate, the only preparations capable of normalising the defect in patients with von Willebrand's disease, showed the same level of VIIIR:Ag determined by EI and by IRMA, while all the other preparations (i.e. cryoprecipitates purified further in different ways) had considerably lower levels of VIIIR:Ag determined by IRMA than by EL Based on these in vitro techniques it seems to be possible to predict which preparations can be used successfully in patients with von Willebrand's disease, while no such conclusions can be made from VIIIR:RCF determinations. EI yielded similar concentrations of factor XIII a subunit in all the preparations tested. 3 functional assays showed high factor XIII activities in AHF-Kabi but low or no activities in the others. Thus, considerable differences were found of the in vitro properties of the proteins in 5 factor VIII concentrates and a cryoprecipitate. The action of proteases and the techniques used in the purification procedure are probably of crucial importance for the properties of the various factors.     

Use of a Simple Visual Assay of Willebrand Factor for Diagnosis and Carrier Identification

A visual assay of factor VIII-related Willebrand factor (VIIIR:WF) is described which utilizes formaldehyde-fixed platelets, end points being read in microflocculation tiles. Four dilutions of a sample can be assessed simultaneously, and the correlation with aggregometric assays is high (r = 0.91). Measurement error is 8.0% for a single assay in triplicate and less than 5% if an assay is repeated three times. The method has been used for 2 years by the coagulation genetics group at Chapel Hill for diagnosing subjects with von Willebrand's disease and assigning genotypes to members of families transmitting this disorder. Its utility in classifying known carriers of haemophilia A has also been examined, both in conjunction with assays of VIII:C and in a three-way test with assays of VIII:C and VIIIR:Ag. As predicted by the Lyon hypothesis, the rate of false negative diagnosis was higher than false positive diagnosis, but the overall rate of misclassification on single plasma samples was 7/51 = 13.7%. The error rate was the same whether discrimination was based upon assays of VIII:C vs. VIIIR:Ag, VIII:C vs. VIIIR:WF, or VIII:C vs. VIIIR:Ag vs VIIIR:WF, the same individuals being misclassified by each method. The observed rate of misclassification was well within the rates reported by others and very similar to our previous experience. We have concluded that this method of assaying VIIIR:WF is highly useful for diagnosing vWd, detecting inhibitors to VIIIR:WF, and examining large numbers of column fractions. It is a useful supplement, although it cannot yet substitute for, assays of VIIIR:Ag in detecting carriers of haemophilia A.     

Relationships between metabolic and hemostatic variables in uncomplicated diabetes

Summary Several metabolic (HbA₁, HDL-C, triglycerides) and hemostatic (VIIIR:Ag, VIII:C, B-TG) variables were investigated in 35 non-obese, insulin-dependent diabetics without clinically evident vascular complications. B-TG was high but did not correlate with other metabolic and hemostatic parameters, suggesting that elevated B-TG in diabetes might be an expression ofin vitro platelet activation. VIIIR:Ag and the ratio of VIIIR:Ag to VIII:C were markedly increased. There was a significant correlation of the HbA₁ and HDL-C levels with VIIIR: Ag, indicating that VIIIR:Ag is another reflection of metabolic control in diabetes. Additional pathogenic mechanisms, however, appear to be involved in causing the changes in VIIIR: Ag in diabetes.     

Factor VIII complex in progressive systemic sclerosis

Factor VIII complex and its related activities (Coagulant, Antigen and Ristocetin Cofactor) have been investigated in 23 patients with Progressive Systemic Sclerosis (PSS) divided into two groups: acrosclerosis and diffuse sclerosis. All Factor VIII-related activities were higher in PSS patients than in normal subjects. No difference in F. VIII-related Antigen (F. VIIIR:Ag), F. VIII-related Ristocetin Cofactor (F. VIIIR:Co) and F. VIII Coagulant activity (F. VIII:C) was found comparing the patient groups. F. VIII:C was increased significantly less than F. VIIIR:Ag and F. VIIIR:Co in both patient groups. Some hypotheses about the pathogenesis of this increase are discussed.     

The Release of Plasminogen Activator and Factor VIII after Injection of DDAVP in Healthy Volunteers and in Patients with von Willebrand's Disease

Increases in plasma concentrations of VIII:C, VIII:CAg, VIIIR:Ag and plasminogen activator (PA) were observed in 50 healthy volunteers given i.v. injections of DDAVP (desaminocys¹-8-D-arg-vasopressin). The PA activity reached its maximum immediately after the injection, VIII:C, VIII:CAg and VIIIR:Ag after 3040 min. However, a positive correlation was found when the PA and VIII:C responses in each of the normals were analysed. DDAVP was also administered to 3 patients with severe von Willebrand's disease. 2 of the patients displayed no changes in VIII:C, VIII:CAg, VIIIR:Ag or VIIIR:RCF and there was no increase in PA. The third patient responded with an increase in VIII:C and to a minor degree in VIII:CAg. This patient developed fibrinolytic activity, but in the lower normal range. In 3 other patients with mild von Willebrand's disease DDAVP caused increases in VIII:C, VIII:CAg, VIIIR:Ag and PA. We feel that the combined data may support the concept that one and the same target cell is involved in the DDAVP mediated release of factor VIII related activities and PA.     

Alterations of Factor VIII von Willebrand Factor in Clinical Conditions Associated with an Increase in its Plasma Concentration

Factor VIII-related antigen (VIIIR:Ag) was consistently higher than factor-VIII procoagulant activity (VIII:C) in 57 patients with clinical conditions characterized by acute-phase reactions. Two different methods for measuring VIII:C (one- and two-stage assays) and VIIIR:Ag (electroimmunodiffusion and immunoradiometric assay) gave concordant results in the majority of cases. In 43% of plasma samples, crossed immunoelectrophoresis in agarose gel was characterized by the appearance of an additional, fast-moving precipitin peak which was immunologically identical with the major, slower-moving VIIIR:Ag peak. The fast-moving peak was detected in all the patients with clinical conditions typically associated with increased plasma proteolysis (DIC, acute pancreatitis, during thrombolytic therapy). It was present in a smaller proportion of cases with liver and renal failure and malignancies and in the post-operative period. The additional VIIIR:Ag peak is thought to be the result of in vivo factor VIII/von Willebrand factor fragmentation by proteolytic enzymes.     

The Separation of Willebrand Factor from Factor VIII-Related Antigen

The three activities associated with factor VIII--coagulant (VIII:C), antigenic (VIIIR:Ag), and platelet agglutinating or Willebrand factor (VIIIR:WF)--have been separated by sequential antibody affinity chromatography, utilizing a rabbit antibody to factor VIII and a spontaneous human antibody to VIII:C. Normal plasma differentially lost its factor VIII-related antigen following passage over the rabbit antibody column. Subsequent passage of the VIIIR:Ag-depleted plasma over the human antibody column resulted in the loss of VIII:C activity, with retention of the Willebrand factor activity, antigen being partially recovered from the heterologous antibody column. These experiments demonstrate that it is possible to separate two of the factor VIII activities, VIIIR:Ag and VIIIR:WF, which are usually regarded as properties of a single molecule.     

A comparative study of carrier detection in haemophilia A by linear discriminant function

S ummary . Blood samples collected from 37 definite carriers, 31 normal women and 64 possible carriers were examined for factor VIII-related activities. Five variables: factor VIII coagulant activity (VIII:C) (X₁), factor VIII-related antigen (VIIIR:Ag) (X₂), ristocetin co-factor (VIIIR:RC) (X₃), ratio of VIIIR: Ag to VIII:C (A/C) (X₄) and ratio of VIIIR: RC to VIII:C (R/C) (X₅), and 28 combinations of one to five variables were used to derive 28 linear discriminant functions. The calculation of discriminant function coefficient, individual discriminant score and cut-off point, and the identification of normals or carriers were processed by the computer package of a biomedical computer program used at University of California at Los Angeles.
A comparison of 28 linear discriminant functions for carrier detection in haemophilia A has indicated that the best and simplest is y=0.11668X₁ (VIII:C)-0.06042X₂ (VIIIR:Ag), (cut-off point =2.03742). It identified 94.6% of carriers without a single misclassification in the normal group, and the overall identification rate was 97.1%. Of 29 daughters of definite carriers who had no haemophilic sons, 13, or 44.8%, could be identified as carriers.
It was found that VIIIR:RC was not as good as VIIIR:Ag for carrier detection; however, it may be concluded from this study that VIIIR:RC can be used as a supplement, if not a substitute, for VIIIR:Ag in the carrier detection of haemophilia A.     

Endothelial Cell Hybrids and the Suppression of Factor VIII Related Antigcn Exprcssion

Hybrid somatic cell clones have been generated by fusing human vascular endothelial cells in primary culture to cells of four rodent lines. Factor VIII related antigen (VIIIR:Ag) was clearly demonstrable in the cultured endothelial cells, even when they had been co-cultured with rodent cells. Hut in none of 14 hybrid clones was VII1R; Ag detectable. Isozyme analyses for human chromosome markers show that all the assayed human chromosomes were represented among the hybrids, and that various subsets of human chromosomes have been deleted from individual hybrid clones. It may be concluded, therefore, either that VIIIR:Ag production depends on a particular combination of human chromosomes not represented in any of the hybrids, or that the rodent cells contribute some agent which intracellularly blocks VIIIR:Ag expression.     

Factor VIII concentrate prepared from DDAVP stimulated blood donor plasma.

Human fraction I-0 (AHF-Kabi) was prepared from plasma from blood donors who had received an i.v. injection of DDAVP (0.2 microgram per kg b.w.) and tranexamic acid (0.01 g per kg b.w.) 15 min before collection of the blood. The factor VIII preparation from such plasma contained twice as much VIII:C,VIIIR:Ag, and VIIIR:RFC as normal fraction I-0. Normal fraction I-0 and DDAVP fraction I-0 were given to 2 patients with severe haemophilia A. The in vivo response of the DDAVP fraction I-0 corresponded to the in vitro values. No differences in survival time were seen. Hence, it is possible to produce factor VIII concentrates with at least double the yield by increasing the factor VIII level in blood donors by i.v. injection of DDAVP.     

Changes in coagulation and fibrinolysis after total hip replacement and their relations with deep vein thrombosis

Postoperative changes related to coagulation and fibrinolysis and their correlation with the incidence of deep venous thrombosis (DVT) were studied in 30 patients undergoing total hip replacement. Pre- and postoperative measurements of fibrinogen, factor Xa, VIII:C, VIIIR:Ag and its electrophoretic mobility, antifactor Xa activity, antithrombin III (AT III) and its electrophoretic mobility in plasma and serum, fibrin monomers, euglobulin lysis time, fibrinogen degradation products (FDP), alpha 2-antiplasmin and plasmin-antiplasmin complexes were determined. DVT was detected by 125I-fibrinogen leg scanning in 11 patients. There was a significant and progressive increase in fibrinogen, VIII:C, VIIIR:Ag, fibrin monomers, FDP and alpha 2-anti-plasmin levels after operation and likewise a prolongation of euglobulin lysis time. There were changes in electrophoretic mobility of AT III in plasma and serum in 12 patients. The presence of plasmin-antiplasmin complexes was demonstrated in 9 patients. No correlation between the changes in coagulation and fibrinolysis and the incidence of postoperative DVT was found. We conclude that important changes occur in several parameters of coagulation and fibrinolysis after total hip replacement. Such changes are not related to the development of postoperative DVT.     

Immunological Evidence that Human Factor VIII is Composed of Two Linked Moieties

The relationship between the three measurable components of the factor VIII complex, procoagulant activity (VIII:C), Ristocetin cofactor (VIIIR:WF) and factor VIII related antigen (VIIR:AG), has been investigated using a solid phase immunoadsorption system in which homologous antibodies specific for VIII:C are insolubilized onto Sepharose beads. The VIII:C component of partially purified factor VIII can be completely separated from the Willebrand factor (VIIIR:WF/VIIIR:AG) by this technique. The loss of VIII:C has no detectable effect on the molecular size, antigenicity or electrophoretic mobility of the original molecule. The Willebrand factor (WF) recovered from these immunoadsorption columns was used to absorb heterologous antisera to factor VIII. A specific heterologous antiserum to VIII:C, which no longer neutralized VIIIR:WF nor precipitated VIIIR:AG, was obtained. Heterologous antisera to WF were prepared which potently neutralized VIIR:WF and precipitated with VIIIR:AG, but also weakly neutralized VIII:C (titre I u/ml). This study is compatible with the theory that VIII:C and VIIIR:WF/VIIIR:AG are two different but linked entities.     

Factor VIII Procoagulant Activity, Factor VIII Related Antigen and von Willebrand Factor in Newborn Cord Blood

The mean level of factor VIII procoagulant acitivity (VIII:C) and factor VIII related antigen (VIIIR:AG) was normal in 100 newborn cord plasmas, whereas that of von Willebrand factor (VIIIR:WF) activity was slightly lower than normal. On crossed immunoelectrophoresis, 20 of 50 newborn infants had an increased anodal mobility of VIIIR:AG. When the cord plasma showing an abnormal electrophoretic pattern was mixed with normal plasma, two precipitation peaks with a broad base were found. Similar mixing experiments with the abnormal cord plasma and plasma from a patient with atypical von Willebrand's disease did not normalize the electrophoretic mobility of VIIIR:AG. Gel filtration of the cord plasma with an abnormal electrophoretic pattern of VIII:AG, showed that the three activities were all detected at the position corresponding to a molecular weight of about 800 000. The results suggest the presence of qualitative abnormalities of the factor VIII molecule in half of full-term newborn cord plasma.     

Factor VIII Concentrate Prepared from DDAVP Stimulated Blood Donor Plasma

Human fraction 1-0 (AHF-Kabi) was prepared from plasma from blood donors who had received an i.v. injection of DDAVP (0.2 μg per kg b.w.) and tranexamic acid (0.01 g per kg b.w.) 15 min before collection of the blood. The factor VIII preparation from such plasma contained twice as much VIII:C, VIIIR:Ag, and VIIIR:RFC as normal fraction 1-0. Normal fraction 1-0 and DDAVP fraction 1-0 were given to 2 patients with severe haemophilia A. The in vivo response of the DDAVP fraction 1-0 corresponded to the in vitro values. No differences in survival time were seen. Hence, it is possible to produce factor VIII concentrates with at least double the yield by increasing the factor VIII level in blood donors by i.v. injection of DDAVP.     

Serial studies in von Willebrand's disease: variability versus "variants"

The variability of laboratory findings in von Willebrand's disease (vWd) was evaluated by performing serial studies of bleeding time (BT), factor VIII coagulant activity (VIII:C), factor-VIII-related antigen (VIIIR:Ag) and ristocetin cofactor (VIIIR:Rcof) in 50 individuals from 25 families with this disorder. The types of results were characterized from 1 to 16 based on the possible combinations of findings using these four tests. The only patients observed to have consistently abnormal results of all four tests were three individuals with homozygous vWd. Individuals with autosomal dominant vWd were found to have a variety of results and all 16 possible types were observed. Although a consistent pattern was present within some families, others with equivalent history of bleeding demonstrated widely variable types of results. The results within some families, others with equivalent history of bleeding demonstrated widely variable types of results. The results of serial studies of the same tests in 10 normal individuals indicated relative stability, with nearly all values within the usual range of normal, but some independent variation of factor-VIII-related activities was observed. These studies indicate that: (1) the results of BT, VIII:C, VIIIR:Ag, and VIIIR:Rcof vary considerably from time to time in many individuals with vWd, (2) a classification of "variants" of vWd based solely on such studies may be inappropriate, particularly if the tests are not repeated, and (3) repeated testing may be required to establish the diagnosis of vWd in some individuals.     

Replacement therapy in platelet-type von Willebrand disease

The response to infusions of cryoprecipitate and factor VIII concentrate was studied in a patient with platelet-type von Willebrand disease (vWD) who showed lack of the large multimers of von Willebrand factor in plasma, increased platelet aggregation with low concentrations of ristocetin, and in vitro platelet aggregation by normal plasma. The cryoprecipitate and factor VIII concentrate to be infused induced platelet aggregation when added to patient platelet-rich plasma at concentrations higher than 0.86 U/ml and 3 U/ml of factor VIII-related antigen (VIIIR:Ag), respectively. Administration of cryoprecipitate (41.9 U VIIIR:Ag/kg body weight) was followed by a shortening of the bleeding time, and hemostasis was achieved during tooth extractions. Factor VIII concentrate (70.2 U VIIIR:Ag/kg) failed to correct the prolonged bleeding time and proved ineffective to control the gum bleeding. No significant diminution of the platelet count was observed following any infusion. These results indicate that cryoprecipitate is hemostatically effective and safe when infused in such a dosage, but factor VIII concentrate is not effective in platelet-type vWD in analogy to what is observed in various types of vWD.     

Characteristics of Various Factor VIII Concentrates used in Treatment of Haemophilia A

Summary . Five different factor VIII concentrates, AHF-Kabi (fraction I-o), Krynativ-Kabi (freeze-dried cryoprecipitate), Hemofil-Hyland, AHF-profilate-Abbott, Kryobulin-Immuno, available in Sweden for treatment of haemophiliacs were compared with respect to in vivo recovery, half-life of factor VIII clotting activity (VIII:C) and in vitro properties. The parameters studied were VIII:C, factor VIII related antigen (VIIIR:AG), crossed immunoelectrophoresis, ristocetin co-factor activity (VIII: Rcof), fibrinogen content and factor XIII activity. AHF-Kabi had the lowest concentration of VIII:C. All the preparations had higher values for VIIIR:AG than for VIII:C. The quotient was highest for Hemofil, Krynativ-Kabi and Kryobulin and varied between 4 and 7. The lowest quotient, 1.3 to 4, was that of AHF-Kabi. The number of units of VIII: Rcof was almost the same as that of VIII:C. AHF-Kabi had the highest fibrinogen concentration and was the only preparation with high amounts of F XIII. In crossed immunoelectrophoresis AHF-Kabi showed a similar pattern to that of normal plasma. The other preparations had a different pattern suggesting less heterogenicity of the molecule. The in vivo recovery was about the same for all the concentrates. The disappearance rate of VIII:C after infusion of corresponding doses of the different concentrates was studied in six patients with severe haemophilia A who were not bleeding. AHF-Kabi had a half-life between 18 and 26 h which was substantially longer than any of the other preparations. The half-life of Hemofil, Krynativ-Kabi, AHF-Profilate and Kryobulin varied between 8 and 16 h. The concentrates were given to three patients with severe classical von Willebrand's disease. All the preparations caused an increase of VIII:C and VIIIR:AG as well as of VIII:Rcof, but only AHF-Kabi corrected the prolonged bleeding time. Knowledge of the properties of various VIII concentrates is of importance for the choice of treatment in haemophilia and von Willebrand's disease.