Baseline characteristics and outcomes of children with cancer in the English-speaking Caribbean: A multinational retrospective cohort.

BACKGROUND: English-speaking Caribbean (ESC) childhood cancer outcomes are unknown. PROCEDURE: Through the SickKids-Caribbean Initiative (SCI), we established a multicenter childhood cancer database across seven centers in six ESC countries. Data managers entered patient demographics, disease, treatment, and outcome data. Data collection commenced in 2013, with retrospective collection to 2011 and subsequent prospective collection. RESULTS: A total of 367 children were diagnosed between 2011 and 2015 with a median age of 5.7 years (interquartile range 2.9-10.6 years). One hundred thirty (35.4%) patients were diagnosed with leukemia, 30 (8.2%) with lymphoma, and 149 (40.6%) with solid tumors. A relative paucity of children with brain tumors was seen (N = 58, 15.8%). Two-year event-free survival (EFS) for the cohort was 48.5% ± 3.2%; 2-year overall survival (OS) was 55.1% ± 3.1%. Children with acute lymphoblastic leukemia (ALL) and Wilms tumor (WT) experienced better 2-year EFS (62.1% ± 6.4% and 66.7% ± 10.1%), while dismal outcomes were seen in children with acute myeloid leukemia (AML; 22.7 ± 9.6%), rhabdomyosarcoma (21.0% ± 17.0%), and medulloblastoma (21.4% ± 17.8%). Of 108 deaths with known cause, 58 (53.7%) were attributed to disease and 50 (46.3%) to treatment complications. Death within 60 days of diagnosis was relatively common in acute leukemia [13/98 (13.3%) ALL, 8/26 (30.8%) AML]. Despite this, traditional prognosticators adversely impacted outcome in ALL, including higher age, higher white blood cell count, and T-cell lineage. CONCLUSIONS: ESC childhood cancer outcomes are significantly inferior to high-income country outcomes. Based on these data, interventions for improving supportive care and modifying treatment protocols are under way. Continued data collection will allow evaluation of interventions and ensure maximal outcome improvements.

In vitro and in vivo stability of diluted recombinant factor VIII for continuous infusion use in haemophilia A.

Factor VIII (FVIII) replacement by continuous infusion (CI) is used postoperatively or after significant bleeding. For young paediatric patients, CI may require FVIII dilution. Variable stabilities of diluted full-length recombinant FVIII Kogenate FS (KG-FS) have been reported under different storage conditions. We investigated the recovery and stability of diluted KG-FS in vitro and in vivo. Kogenate FS was diluted to 50-120 U mL(-1) and its recovery and stability in glass vials or polypropylene syringes was determined. Furthermore, stability of KG-FS diluted to 80 U mL(-1)'administered' via single- and double-pump mock CI systems was tested. Finally, the in vivo stability of KG-FS diluted to approximately 60 U mL(-1) and administered postsurgically by CI with the double-pump to a paediatric patient with severe haemophilia A undergoing implantable venous access device placement was investigated. Initial KG-FS dilution resulted in a 10-20% FVIII loss; a further 25-30% loss occurred over 72 h in vials or syringes. With the double-pump, 1 h recovery was 35%, increasing to 80% by 24 h; the initial losses were because of the Y-infusion of a 10-fold larger volume of saline concomitantly with the FVIII. In vivo, CI resulted in stable FVIII activity levels within the target range. These in vitro results are important for the generation of CI guidelines for diluted KG-FS in the paediatric haemophilic population. That FVIII losses occur upon dilution and with the double-pump does not preclude use of diluted KG-FS. Indeed, stable FVIII levels were maintained when diluted KG-FS was administered by CI with the double-pump to a paediatric patient postsurgically.

Comparing two measures of quality of life for children with haemophilia: the CHO-KLAT and the Haemo-QoL.

Disease-specific measures of quality of life (QoL) for children with haemophilia are now available for use in clinical studies [Haemophilia, 10, 2004, 9-16]. One of these measures, the Canadian Haemophilia Outcomes - Kids' Life Assessment Tool (CHO-KLAT), was developed in Canada with emphasis on the perspectives of children [Pediatr Blood Cancer, 47, 2006, 305-11; Haemophilia, 10, 2004, 34-43]. Another, the Haemo-QoL, was developed in Europe, with emphasis on the perspectives of clinicians [Haemophilia, 8, 2002, 47-54; Haemophilia, 10, 2004, 17-25]. While these two measures are unique and independent, researchers from both studies were collaboratively linked throughout development and testing. This study presents the results of a joint assessment of the two measures with respect to their strengths, limitations and unique contributions. The primary questions addressed were: 1 What is the relationship between the CHO-KLAT and the Haemo-QoL in terms of summary scores and item content? 2 What are the methodological strengths, limitations and unique contributions of each measure? We conducted a retrospective analysis of data from field testing of both measures. The analysis included a comparative assessment of the basic validity, reliability and items used in each measure. Overall, the CHO-KLAT and the Haemo-QoL are promising and valuable measures of QoL for children with haemophilia. Our analyses confirmed the basic psychometric properties of both tools, but identified some discrepancies between them. Additional data will allow for greater understanding of these discrepancies and lend clarity to how the tools should be used in clinical studies (separately or merged). The present recommendation is that the measures be run independently, but preferably concurrently in studies of children with haemophilia.

A laparoscopic approach to partial splenectomy for children with hereditary spherocytosis.

BACKGROUND: Partial splenectomy is sometimes used for children with hereditary spherocytosis (HS) to reduce hemolysis while retaining some splenic immune function. Previous reports have described a partial splenic resection through a laparotomy incision. Whereas laparoscopic total splenectomy for HS is well-established, laparoscopic partial splenectomy (LPS) has not been described. The authors have developed a novel LPS technique that combines the benefits of partial splenectomy with those of a laparoscopic approach. METHODS: A chart review was conducted for three children with HS who underwent LPS, with approximately one-fourth of the spleen left on the basis of the short gastric arterial supply. RESULTS: The mean preoperative spleen size was 17.6 cm. The mean preoperative hemoglobin count was 100 g/l, and the postoperative hemoglobin count was 133 g/l. All three patients reported reduced malaise and increased energy levels. There was no recurrent anemia at the 1- to 2-year follow-up evaluation. CONCLUSION: The LPS procedure is a safe and effective approach to HS that resolves anemia, potentially retains some splenic immunity, and confers the benefits of a minimal access technique.

Hemophilia therapy innovation: development of an advanced category recombinant factor VIII by a plasma/albumin-free method. Proceedings of a Special Symposium at the XIXth Congress of the International Society on Thrombosis and Haemostasis, July 12-18, 2003, Birmingham, UK.

Replacement therapy for hemophilia A has evolved from the early use of whole blood, citrated plasma, and cryoprecipitate, to purified factor VIII (FVIII) concentrates, first derived from plasma, then produced by recombinant DNA technology. Recombinant FVIII (rFVIII) concentrates have provided improved safety for patients with hemophilia A since they significantly reduce the risk of transmission of blood-borne infections. Nevertheless, human- or animal-derived plasma proteins are still included at some step in preparation of all previously licensed rFVIII, thereby introducing the potential for transmission of human or animal pathogens. Anti-hemophilic factor (recombinant), plasma/albumin-free method (rAHF-PFM), a novel advanced category rFVIII produced without the addition of human or animal plasma proteins, has been developed with the goal of providing the greatest possible margin of safety to hemophilia patients. This report, based on a symposium of the XIXth International Society on Thrombosis and Haemostasis Congress, provides an overview of the rAHF-PFM development program as well as current findings from the global clinical evaluation of rAHF-PFM in pediatric and adult previously treated patients.

Intensive exposure to factor VIII is a risk factor for inhibitor development in mild hemophilia A.

BACKGROUND: Inhibitors are rare in boys with mild hemophilia A (MHA; factor (F)VIII:C > 5%) but may arise following intense FVIII exposure, e.g. continuous infusion (CI). OBJECTIVES: To determine the impact of intense FVIII exposure in inhibitor formation in MHA at our institution and to compare this with previous reports. PATIENTS AND METHODS: We reviewed FVIII exposure and inhibitor development in boys (ages 0-18 years) with MHA followed at our institution from 1996 to 2001 and conducted a Medline search (1966-2002) on the experience of inhibitor development following intensive/CI exposure to FVIII. RESULTS: We identified 54 boys with MHA. Twenty-nine (54%) had been exposed to FVIII. Seven had received FVIII by CI. Four developed inhibitors; three high titer (at ages 10 years, 16 years and 17 years) and one low titer (at 1 month old). All four had received a CI of recombinant (r) FVIII of at least 6 days within 6 weeks of developing inhibitors. Baseline FVIII levels fell to < 1% in all cases and the three with high-titer inhibitors developed severe bleeding. Immune tolerance therapy (ITT) was attempted in two boys and was successful in one. Our literature search identified 35 cases (only four children) with MHA developing inhibitors following intense FVIII exposure often in the context of surgery. CONCLUSIONS: The incidence of inhibitors in our MHA population was 7.4%. If expressed according to exposure the incidence was significantly higher: 14% (4/29) for any exposure to FVIII and 57% (4/7) for exposure by CI. A prospective study to address whether CI is associated with an increased incidence of inhibitor development in MHA is warranted.

Initial bone marrow aspiration in childhood idiopathic thrombocytopenia: decision analysis.

PURPOSE: Bone marrow aspiration (BMA) is routinely performed before starting steroid therapy in children with idiopathic thrombocytopenia, primarily to rule out leukemia. METHODS: A decision tree for the initial management of a child older than age 6 months, presenting with idiopathic thrombocytopenia, without blasts on the peripheral smear was constructed. The three strategies are: 1) initial BMA in all patients; 2) initial BMA only in patients at high risk; and 3) empiric therapy for all patients without initial BMA. High-risk criteria include any of: platelet count >50 x 10(9)/L; hemoglobin <100 g/L (age younger than 12 months) or <110 g/L (age older than 12 months): white blood cell count <5 x 10(9)/L (younger than 6 years) or <4 x 10(9)/L (older than 6 years); or absolute neutrophil count <1.5 x 10(9)/L (younger than 6 years) or <2 x 10(9)/L (older than 6 years). The results are expressed as quality-adjusted life years (QALYs), a measure that estimates the overall life expectancy in years for patients receiving a particular treatment strategy, corrected for the patient's quality of life. RESULTS: The base case results are: 1) BMA all = 69.649 QALYs; 2) high-risk BMA = 69.652 QALYs; and 3) empiric therapy = 69.644 QALYs. These results indicate a three-way toss-up because there is less than a 4-day quality-adjusted difference (0.01) between strategies. CONCLUSION: This study indicates that the initial BMA does not significantly change the overall QALYs of a child presenting with thrombocytopenia and, consequently, is not mandatory in every patient before starting steroids.

Effect of premedication guidelines and leukoreduction on the rate of febrile nonhaemolytic platelet transfusion reactions.

Platelet transfusion reactions were prospectively studied in haematology/oncology patients at five university teaching hospitals over three consecutive summers. The initial summer study provided baseline information on the use of premedications and the rate of platelet transfusion reactions (fever, chills, rigors and hives). Most (73%) platelet recipients were premedicated and 30% (95% CI 28-33%) of transfusions were complicated by reactions. The second study followed implementation of guidelines for premedicating platelet transfusions. Despite a marked reduction in premedication (50%), there was little change in the platelet transfusion reaction rate, 26% (95% CI 24-29%), or the type of reactions. The third study followed implementation of prestorage platelet leukoreduction while maintaining the premedication guidelines. The reaction rate decreased to 19% (95% CI 17-22%). For nonleukoreduced platelets, there was a statistically significant association between the platelet age and reaction rate (P = 0.04). For leukoreduced platelets, there was no statistically significant association between platelet age and reaction rate (P = 0.5). Plasma reduction of nonleukoreduced platelet products also reduced the reaction rate. These prospective studies document a high rate of platelet transfusion reactions in haematology/oncology patients and indicate premedication use can be reduced without increasing the reaction rate. Prestorage leukoreduction and/or plasma reduction of platelet products reduces but does not eliminate febrile nonhemolytic platelet transfusion reactions.

Unique processing pathways within recipient antigen-presenting cells determine IgG immunity against donor platelet MHC antigens.

Recipient IgG immunity against leukoreduced donor platelets is dependent on indirect T-cell allorecognition and is suppressed in vivo by inhibitors (aminoguanidine, AMG) of inducible nitric oxide synthase (iNOS). To examine recipient processing pathways of donor platelet antigens, enriched macrophages (antigen-presenting cells [APC]) from BALB/c (H-2(d)) mice were pulsed with allogeneic C57BL/6 (H-2(b)) platelets and transfused weekly into naive BALB/c mice. Platelet-pulsed APC stimulated IgG antidonor antibody production in 45% of recipients by the second transfusion and in 100% by the sixth transfusion; this response was enhanced by pulsing in the presence of interferon-gamma. By the sixth transfusion, high-titer IgG1 (mean titer 4990) and IgG2a (1933) isotypes specific for donor major histocompatibility complex (MHC) class I antigens were detected. Platelet pulsing in the presence of AMG or colchicine significantly inhibited the ability of APC to stimulate IgG alloantibodies; only 50% (P <.005) and 20% (P <.0001) of recipients, respectively, produced antibodies by the sixth transfusion. AMG inhibition was reversed by the addition of L-arginine, the substrate for iNOS. In contrast, pulsing in the presence of chloroquine, the proteasome inhibitory peptide MG115, or Brefeldin A enhanced APC immunity (70-100% of recipients antibody positive by the second transfusion [P <.05]); these agents allowed the pulsed APC to stimulate IgG2a but inhibited IgG1 production and this correlated with a reduction in serum interleukin (IL)-4 levels. The results suggest that for donor platelet antigens to stimulate IgG alloantibodies, recipient APC use the essential generation of nitric oxide and a noncytosolic, pH-independent processing pathway, which can be exploited as an effective immunotherapy target to further inhibit alloimmunization against leukoreduced platelets. (Blood. 2000;95:1735-1742)

Improved survival in severe acquired aplastic anemia of childhood.

Multi-agent immunosuppressive therapy has produced improved survival for severe acquired aplastic anemia in children. Recently, some investigators have suggested that immunosuppressive therapy may replace bone marrow transplantation as first-line therapy for this disorder. To assess its validity, we compared the outcomes of bone marrow transplantation vs immunosuppressive therapy in one institution from 1987 to 1997. We studied 46 consecutive patients less than 18 years of age who presented between January 1987 and April 1997. Inherited marrow failure syndromes and myelodysplastic syndromes were excluded. Patients received immunosuppressive therapy vs bone marrow transplantation based on availability of HLA-matched donors. The main outcome measures were survival, complete marrow and hematological remission, or partial remission but achieving independence from transfusional support. Twenty patients received multi-agent immunosuppressive therapy (cyclosporine, antithymocyte globulin and methylprednisolone); 11 attained complete remission and three partial remission for a transfusion-independent survival of 70%. Six patients died of infectious and hemorrhagic complications. Twenty-six patients were transplanted and 24 (93%) achieved complete remission; one achieved a PR, 25 remain transfusion independent with a median follow-up of 5.9 years or 70 months. One patient developed AML 34 months after successful transplant and one patient died due to graft failure and complications of transplant. There has been a striking improvement in survival for pediatric patients treated with multi-agent immunosuppression in the last decade. However, transplantation results have also improved and this remains the definitive first-line therapy for severe acquired aplastic anemia in this age group.

Essential thrombocythemia in children.

PURPOSE: The objective of this study was to evaluate the clinical course, laboratory findings, and outcomes of children with essential thrombocythemia (ET). PATIENTS AND METHODS: The authors analyzed 36 children, ages 6 weeks to 18 years, by combining descriptions of 2 patients observed at their institution with 34 patients reported in the English medical literature. RESULTS: Fifteen patients (10 at diagnosis and 5 later on) had symptoms directly related to ET, including 9 who had severe thrombohemorrhagic phenomena. Common abnormalities included large platelets, increased marrow megakaryocytes with hyperlobulated forms, and abnormal platelet aggregation. Symptomatic patients had significantly higher platelet counts (2,419 versus 904 x 10(9)/L, P < 0.001); however, three patients with platelet counts that were only moderately elevated (600-800 x 10(9)/L) had thrombotic events. Eleven patients received various therapeutic agents. Interestingly, three patients who had one thrombotic event, and did not receive therapy, went on to have a benign clinical course. Leukemia developed in two treated patients, and they died; two others died of thrombotic complications; and myelofibrosis developed in one patient. Seventeen cases (47%) were familial. Patients with familial cases had significantly lower platelet counts, a lower incidence of hepatomegaly, and no thrombotic complications. CONCLUSIONS: This analysis of children with ET found that severe vascular complications developed in a substantial number. Platelet counts usually, but not always, correlate with the occurrence of complications. The indications for treatment and the best treatment of children with ET are currently not known, and guidelines for the management of children with ET are needed. Familial thrombocythemia is common among children with primary thrombocytosis and appears to be a different disease from ET, with a more benign course.

Inhibition of a secondary human alloimmune response via the soluble active component of CD154 (CD40L) in severe combined immune-deficient mice engrafted with human lymphocytes.

BACKGROUND: Alloimmunization requires a process known as co-stimulation. An important co-stimulatory pathway for most immune responses is mediated by the interaction of CD40 on antigen-presenting cells with CD154 (CD40L) on host T cells. Blockade of this co-stimulatory pathway simultaneous with exposure to challenge with HLA-incompatible cells is hypothesized to inhibit alloimmunization. STUDY DESIGN AND METHODS: Severe combined immune-deficient (SCID) mice were reconstituted with human peripheral blood lymphocytes (Hu-PBL-SCID mice) from a subject primed to HLA antigens and challenged with HLA-incompatible lymphocytes. Mice were challenged in the presence or absence of an 18-kDa soluble recombinant active form of human CD154 (18-kDa CD154). Human IgG production, alloimmunization, and in vitro T-cell responsiveness were assessed. RESULTS: There was no significant effect of 18-kDa CD154 on human IgG levels in these mice, but it inhibited the development of HLA-specific alloantibody in this model to five subsequent untreated white cell challenges. In vitro T-cell proliferation in a mixed lymphocyte culture was also prevented by 18-kDa CD154. CONCLUSION: The recombinant protein 18-kDa CD154 inhibited the ability of the Hu-PBL-SCID mice to mount a secondary immune response to allostimulation. This implies that transfusion-induced alloimmunization utilizes CD40-CD154 co-stimulation and that blockade of this pathway can inhibit T-cell function and interfere with the development of alloimmunization.

Reticulated platelet counts in the diagnosis of acute immune thrombocytopenic purpura.

PURPOSE: Bone marrow aspiration is often performed to diagnose childhood acute immune thrombocytopenic purpura (ITP) because no non-invasive investigation to confirm the diagnosis is routinely available. Reticulated platelets (RPs--young platelets characterized by a high RNA content--increase with increased platelet production and may be useful in the diagnosis of ITP. METHODS: To assess the role of RP counts in distinguishing ITP, we compared counts from 15 consecutive patients with ITP with counts from 20 patients with acute lymphoblastic leukemia (ALL), 10 with aplasia, and 27 healthy normal children. Whole blood in edetic acid (EDTA) was labelled with a platelet-specific monoclonal antibody and incubated with thiazole orange (TO). A standard gate was set to achieve a fluorescence value of 1.3 +/- 0.5% for control lyophilized platelets. RESULTS: Patients with ITP had a mean (+/- 1 standard deviation) RP level of 32.9 +/- 10.2%; patients with ALL, 6.6 +/- 3.1%; patients with aplasia, 3.4 +/- 2.0%; and normal patients, 7.9 +/- 2.9%. The difference in RPs between the ITP group and the ALL, aplasia, and normal groups was highly significant (p < 0.0001 each), with no significant difference between the non-ITP groups (p = 0.12). CONCLUSIONS: Measuring RPs by this simple whole-blood cytometric technique discriminated very well between the acute ITP and non-ITP groups. This test has a strong positive predictive value and may prove very useful in the assessment of childhood acute ITP and the screening of candidates for bone marrow aspiration.

Platelet activation induced by porcine factor VIII (Hyate:C).

We studied the effects of porcine factor VIII (P-FVIII; Hyate:C) and other coagulation products employed in the management of patients with hemophilia A, on platelet activation in vitro. Exposure of normal resting platelets to P-FVIII resulted in platelet activation, as manifested by increased expression of the platelet surface activation markers CD62, CD63, and activated-GPIIbIIIa, and by activation-induced modulation of expression of normal platelet membrane glycoproteins CD41, CD42, and CD36. In contrast, platelet activation was not observed after exposure of the platelets to human FVIII, FEIBA, recombinant FVIIa, or cryosupernatant plasma. As with thrombin, exposure of platelets to P-FVIII resulted in the generation of platelet microparticles, an effect not seen not with the other products. In contrast to the characteristic reduction in expression in the number of CD42 molecules detected on thrombin-activated platelets, P-FVIII-stimulated platelets showed a small increase in CD42 expression. In contrast to thrombin, P-FVIII did not cause platelet dense granule release. The results indicate that therapeutic P-FVIII activates platelets, likely in ways that are different from the platelet activation seen with thrombin. The observed platelet activation and microparticle generation may provide a "hypercoagulable" mechanism for hemostasis with P-FVIII therapy separate from, and additional to, that due to increased circulating FVIII levels.

Platelet-surface glycoproteins in healthy and preeclamptic mothers and their newborn infants.

Preeclampsia, a common complication of pregnancy, contributes significantly to maternal and fetal morbidity and mortality. It may lead to both quantitative and qualitative defects of maternal and neonatal platelets. In this prospective study, flow cytometry has been used to study expression of platelet-surface glycoproteins (GPs) on maternal and neonatal platelets of both healthy and preeclamptic subjects. We studied 15 preeclamptic women, 20-44 y of age, and their newborns (median gestational age, 32 wk; range, 26-38) and seven healthy women (aged 26-41 y) and their healthy newborns (median gestational age, 38 wk; range, 38-42). Compared with their healthy and preeclamptic mothers, resting platelets from neonates expressed significantly less CD41 and CD9. Thrombin activation resulted in significant increases in platelet-surface expression of CD62P, CD63, CD41, CD9, and CD36 in neonates and their healthy mothers. Compared with neonates of healthy mothers, platelets from neonates of preeclamptic mothers expressed lower levels of CD62P, CD63, CD9, and CD36 on activated platelets. These findings suggest that preeclampsia influences the expression of platelet-surface GPs on neonatal and maternal platelets, which may affect platelet function, leading to an additional risk for bleeding in thrombocytopenic neonates of mothers with preeclampsia.

Recipient humoral immunity against leukoreduced allogeneic platelets is suppressed by aminoguanidine, a selective inhibitor of inducible nitric oxide synthase.

Leukoreduced allogeneic platelet transfusions have been previously shown to initially stimulate an in vitro cellular cytotoxicity and subsequently Induce the formation of immunoglobulin G (IgG) antidonor alloantibodies. To further characterize these responses and determine if they are related, recipient BALB/c H-2d mice were treated with aminoguanidine (AMG), a selective inhibitor of inducible nitric oxide synthase (iNOS), and transfused weekly with 2 x 10(8) C57BL/6 H2b platelets. In control, non-AMG-treated mice, transfusion significantly (P < .01) increased serum levels of interferon-gamma (IFN-gamma) by day 1 posttransfusion (PT). IFN-gamma returned to pretransfusion levels by day 3 PT, and its production was not affected by AMG treatment. Serum interleukin-4 (IL-4), on the other hand, was undetectable before and during the transfusion protocol. By day 3 PT, recipient spleen cells could mediate in vitro anti-P815 (auto), anti-EL4 (allo), and anti-R1.1 (third-party MHC) cytotoxicity, and these responses were maximal by day 7 PT. Concurrently, a significant reduction in the vitro ability of recipient splenocytes to respond to Concanavalin A (ConA) was observed; this was not seen with lipopolysaccharide (LPS) stimulation. Elevated levels of NO2- were found in the ConA culture supernatants from transfused mice at day 3 PT. Serum antidonor alloantibodies were detected by the fifth platelet transfusion. AMG treatment of recipient mice significantly inhibited the transfusion. Induced cytotoxicity and ConA-stimulated NO2- production, and restored ConA-induced proliferation to normal levels. AMG appeared to selectively inhibit platelet-induced alloantibody production in that it did not affect antibody production induced by transfusions with 10(5) allogeneic leukocytes or by immunization with a foreign protein antigen, human gamma globulin, in adjuvant therapy. These results indicate that an in vivo AMG-sensitive mechanism is essential for recipients to initiate a humoral IgG immune response against allogeneic platelets.

Acquired von Willebrand factor deficiency during high-dose infusion of recombinant factor VIII.

Constant infusion of factor VIII (FVIII) into patients with haemophilia A after major surgery has been recommended as optimal treatment to avoid peaks and valleys in the circulating levels of FVIII and to allow the use of much lower doses of FVIII than are historically required. One of our young patients with severe (< 0.01 U/ml FVIII) haemophilia suffered a subdural haematoma for which he received treatment with 815190 recombinant FVIII (rFVIII) units over a period of 52d. 2 weeks after admission, because of low FVIII levels and the presence of FVIII inhibitors, the infusion rate was increased to > 100 U/kg/h for 14d. During this time the FVIII level fluctuated between 0.6 and 4.2 U/ml. For some period it was not possible to detect ristocetin co-factor activity in this patient's plasma and the von Willebrand factor (VWF) level and VWF multimer pattern resembled those of a patient with von Willebrand's disease. Subsequently, when the rFVIII dose was increased 2-fold, this was not reflected by the plasma level of FVIII although antibodies were not detected. The data suggest that the prolonged infusion of very high levels of rFVIII which is deficient in von Willebrand factor can result in depletion of VWF from existing stores, producing a laboratory picture which is consistent with the diagnosis of von Willebrand's disease. Further, in the absence of complexing with VWF, FVIII appears to be cleared from the circulation at an increased rate. This is expensive and potentially compromising. Therefore, when administering very high doses of FVIII concentrates devoid of VWF for prolonged periods of time, ristocetin cofactor and VWF levels should be monitored.