Summary. Heparin‐induced thrombocytopenia (HIT) is a common adverse effect of unfractionated heparin (UFH) therapy. In contrast, only a few patients have been reported with HIT following low‐molecular‐weight heparin (LMWH) therapy (LMW‐HIT). To define the clinical and biological characteristics of LMW‐HIT, 180 patients treated for suspected HIT at 15 French centres were investigated. Clinical history was recorded and HIT was confirmed in 59 patients with positive serotonin release assay results: 57 of them had high levels of antibodies (Abs) to heparin–platelet factor 4 complexes (H/PF4) and two had Abs to interleukin 8. Eleven patients were treated exclusively with LMWH (LMW‐HIT) and 48 with UFH either alone (UF‐HIT, n = 34) or combined with LMWH (UF/LMW‐HIT, n = 14). The LMW‐HIT and UF‐HIT groups were similar with respect to sex, age, platelet count before heparin therapy, frequency of bleeding and occurrence of disseminated intravascular coagulation. The interval to onset of HIT was longer in LMW‐HIT patients compared with UF‐HIT patients (P = 0·03). Severe thrombocytopenia (platelets < 15 × 109/l) was more frequent in the LMW‐HIT group (P = 0·04). Thrombosis occurred in three of 11 LMW‐HIT patients, i.e. as frequently as in UF‐HIT patients. LMW‐HIT is potentially severe and may be observed after longer heparin treatment compared with UF‐HIT. It is highly recommended, therefore, that platelet counts be monitored carefully whenever LMWH is administered.
A randomized study comparing the efficacy and safety of nadroparin 2850 IU (0.3 mL) vs. enoxaparin 4000 IU (40 mg) in the prevention of venous thromboembolism after colorectal surgery for cancer Summary. Background: The optimal thromboprophylactic dosage regimen of low-molecular-weight heparins in high-risk general surgery remains debatable. Objectives: We performed a randomized, double-blind study to compare the efficacy and safety of nadroparin 2850 IU (0.3 mL) and enoxaparin 4000 IU (40 mg) in the prevention of venous thromboembolism (VTE) after colorectal surgery for cancer. Patients and methods: Patients undergoing resection of colorectal adenocarcinoma were randomized to receive once daily either 2850 IU nadroparin or 4000 IU enoxaparin s.c. for 9 ± 2 days. The primary efficacy outcome was the composite of deep vein thrombosis (DVT) detected by bilateral venography or documented symptomatic DVT or pulmonary embolism up to day 12. The main safety outcome was major bleeding. A blinded independent committee adjudicated all outcomes. Results: Out of 1288 patients analyzed, efficacy was evaluable in 950 (73.8%) patients. The VTE rate was 15.9% (74/464) in nadroparintreated patients and 12.6% (61/486) in enoxaparin-treated patients, a relative risk of 1.27 (95% confidence interval; CI: 0.93-1.74) that did not met the criterion for non-inferiority of nadroparin. The rate of proximal DVT was comparable in the two groups (3.2% vs. 2.9%, respectively), but that of symptomatic VTE was lower in nadroparin-treated patients (0.2% vs. 1.4%). There was significantly (P ¼ 0.012) less major bleeding in nadroparin-than in enoxaparin-treated patients (7.3% vs. 11.5%, respectively). Conclusion: Compared with those receiving enoxaparin 4000 IU, patients treated with nadroparin 2850 IU showed a higher incidence of asymptomatic distal DVT, but a lower incidence of symptomatic VTE. Nadroparin treatment was safer in terms of bleeding risk.
SummaryThe incidence of factor VIII inhibitor was studied in a cohort of 56 previously untreated patients with severe hemophilia A (factor VIII below 1 U/dl). They received only one brand of highly purified factor VIII concentrate (HPSD-VIII) prepared by conventional chromatography with a solvent-detergent step for viral inactivation. Followup since the first infusion of HPSD-VIII was from 1 to 76 months (mean = 29) and cumulative exposure days (CED) from 1 to over 100 (median = 26). Five patients (9%) developed an inhibitor after 6 to 19 CED, only one being a high responder (2%), showing a low incidence of inhibitor compared with previous studies using high purity plasma- derived or recombinant products.
We recently reported that after activation of human platelets by thrombin, glycoprotein (GP) Ib-IX complexes are translocated to the surface-connected canalicular system (SCCS) (Blood 76:1503, 1990). As GPIb is a major receptor for von Willebrand factor (vWF) in platelet adhesion, we have now examined the consequences of thrombin activation on the organization of vWF bound to GPIb on the platelet surface. Studies were performed using monoclonal or polyclonal antibodies in either immunogold staining and electron microscopy (Au-EM) or in flow cytometry. When unstirred platelet-rich plasma was incubated with ristocetin, bound vWF was located by Au-EM as discrete masses regularly distributed over the cell surface. Platelets from a patient with Glanzmann's thrombasthenia, lacking GPIIb-IIIa complexes, gave a similar pattern, confirming that this represented binding to GPIb. That ristocetin was not precipitating vWF before their binding to the platelets was shown by the detection of similar masses on the surface of platelets of a patient with type IIB von Willebrand disease. Experiments were continued using washed normal platelets incubated in Tyrode-EDTA, the purpose of the EDTA being to limit the surface expression of endogenous vWF after platelet stimulation. Under these conditions, platelets were treated with ristocetin for 5 minutes at 37 degrees C in the presence of increasing amounts of purified vWF. This was followed by incubation with thrombin (0.5 U/mL) for periods of up to 10 minutes. Flow cytometry showed a time-dependent loss in the surface expression of vWF bound to GPIb and these changes were confirmed by Au-EM. In particular, immunogold staining performed on ultrathin sections showed that the bulk of the vWF was being cleared to internal membrane systems. Surface clearance of vWF during thrombin- induced platelet activation is a potential mechanism for regulating platelet adhesivity.
Type IIA and IIB von Willebrand disease (vWD) result from qualitative abnormalities of von Willebrand factor (vWF) characterized by an absence in plasma of high molecular weight vWF multimers and an abnormal reactivity of vWF towards platelet glycoprotein (GP) Ib, which is decreased in type IIA and increased in type IIB. In this report, we describe the case of a patient having a IIA vWD phenotype associated with an intermittent thrombocytopenia atypical in this subtype but observed in type IIB vWD. The patient plasma vWF showed an absence of high molecular weight and intermediate multimers and had a decreased binding capacity to GPIb. The affinity of botrocetin was normal for plasma vWF from the propositus. Analysis of the propositus vWF gene showed the presence of a substitution Val 551 to Phe of the mature vWF subunit. This mutation is localized within a 509–695 disulphide loop of the vWF that plays an important role in the binding to GPIb and is where most of the molecular defects described so far were associated with type-IIB vWD. We have reproduced the Val 551 Phe substitution onto the vWF cDNA, expressed it in COS-7 cells, and performed structural and functional analysis of the mutant recombinant protein (rvWFPhe 551). The rvWFPhe 551 had a normal multimeric structure and showed the capacity to spontaneously interact with GPIb. Botrocetin had a decreased affinity for rvWFPhe 551. In conclusion, the Val 551 Phe mutation modifies the affinity of vWF for platelet GPIb, as does a type IIB mutation, and may be responsible for the thrombocytopenia of the patient and the clearance of the high molecular weight and intermediate-sized multimers of vWF from the plasma. The study of the rvWFPhe 551 has confirmed the discrepancy between the IIA phenotype and the IIB genotype of the patient.
Profound and complex coagulation disorders are encountered during liver transplantation. They include preoperative coagulation disorders related to the liver disease and haemostatic changes related to the procedure itself. They commonly lead to increased intraoperative bleeding, especially due to increased fibrinolysis, the contribution of which can be demonstrated by the relative efficacy of antifibrinolytics. Given the multifactorial nature of bleeding in liver transplantation, preoperative coagulation tests cannot predict blood loss even if some statistical relationship is occasionally found. Preoperative correction of coagulation defects has not been shown to be effective in reducing intraoperative bleeding. Throughout the procedure, a rapid and sensitive method for monitoring coagulation is necessary in order to guide the rational use of blood components and pharmacological agents. The usefulness of such a method to assist management of blood loss or blood component requirements is poorly documented and controversial.
von Willebrand disease (vWD) type IIB is characterized by an increased reactivity of von Willebrand factor (vWF) with platelets and a lack of large multimers. Exon 28 of the vWF gene encodes for functional domains involved in the binding of vWF to GPIb, and it is presumed that the defects in type IIB vWD lie within or adjacent to these functional domains. We screened overlapping DNA fragments generated by the polymerase chain reaction (PCR) that spanned the 1,379 bp of exon 28 of a type IIB vWD patient using denaturing gradient gel electrophoresis (DGGE). To increase the power of DGGE to detect base changes, we used the PCR to attach a G + C-rich sequence. In the type IIB patient, a DNA fragment at the 5′ end of exon 28 demonstrated homoduplex and heteroduplex complexes after DGGE, a pattern characteristic of heterozygous genes after melting and reannealing during the PCR. Sequencing of the cloned insert from the patient showed a duplication of an ATG in one gene coding for a Met at amino acids 540 to 541 in the mature vWF subunit. This duplication leads to three consecutive methionines in the patient's sequence. The duplicated Met resides within a disulfide bond loop proposed to be important in the function of the GPIb binding domain of vWF. The patient's nephew, who also has type IIB vWD, showed the same duplicated codon, linking the defect to the abnormal phenotype in this family. These nucleotide changes were not found in 100 chromosomes analyzed either by DGGE or hybridization with an allele specific oligonucleotide containing the duplicated ATG codon. In addition, the same oligonucleotide hybridized only to DNA from type IIB vWD individuals and not to DNA from normal members of the family. Therefore, we conclude that this duplicated Met modifies the GPIb binding domain of vWF and causes type IIB vWD in this family.
Using a binding assay to immobilized factor VIII (F VIII) (ELISA) we measured the amount of IgG with binding capacity to FVIII, in the plasma of patients with an inhibitor to F VIII, in multitransfused haemophiliacs without inhibitor and in a control group of blood donors. It was shown that the amount of IgG bound to VIII was elevated in patients with an inhibitor although a weak correlation could be established between the inhibitor titre (BU) and the amount of bound IgG. In all haemophiliacs without inhibitor, IgG bound to F VIII were present. Although the mean value of IgG bound to F VIII was significantly lower than the amount detected in patients with F VIII inhibitors, a group of patients developed an equal amount of IgG recognizing the F VIII molecules to the amount of IgG measured in inhibitor patients. These results indicate that the presence of an inhibitor is not related to the amount of specific IgG bound to F VIII but more likely to the position of epitopes recognized by specific IgG. The presence of IgG bound to F VIII was detected in 92% of control blood donors and an inhibitor to F VIII ranging from 0.5 to 1.3 BU mL(-1) in 17% of them. The isotypes of bound immunoglobins were identified in patients and controls: IgG4 subclass was predominant only in patients with an inhibitor and usually associated with antibodies of one or more of the other subclasses. In noninhibitor patients, very few had antibodies of IgG4 subclass with binding capacity to F VIII. These results raised the question of the clinical significance of these antibodies in multitransfused patients. The study indicates that binding assay is a complementary test to be used in multitransfused patients but cannot be used instead of the coagulation tests for detection of inhibitors.
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