Rational use of the PFA-100 device for screening of platelet function disorders and von Willebrand disease

Maternal Coagulation Disorders and Postpartum Hemorrhage

Coagulation disorders are rare causes of postpartum hemorrhage. Disturbances in coagulation should be suspected in patients with a family history of coagulopathy, those with a personal history of heavy menstrual bleeding, and those with persistent bleeding despite correction of other causes. The coagulopathic conditions discussed include disseminated intravascular coagulation, platelet disorders, and disturbances of coagulation factors. These should not be overlooked in the evaluation of obstetric hemorrhage, as diagnosis and appropriate treatment may prevent severe maternal morbidity and mortality.

Testing strategies used in the diagnosis of rare inherited bleeding disorders

INTRODUCTION

Rare Bleeding Disorders have a low population prevalence and may not be recognized by most clinicians. In addition, knowledge gaps of the indicated laboratory tests and their availability add to the potential for delayed diagnosis or misdiagnosis. The lack of widely available commercial, regulatory body approved esoteric tests limit them to reference laboratories, thus limiting easy access for patients.

AREAS COVERED

A literature search of Pubmed, Medline, Embase and review of international society guidelines was performed. Additional references from published articles were reviewed. A patient-centered approach to recognition and evaluation of RBD is discussed.

EXPERT OPINION

Recognition of RBD relies on obtaining a detailed patient personal and family hemostatic history. Inquiry into a history of involvement of other organ systems is important and if present should lead to suspicion of an inherited platelet disorder or a variant of Ehlers Danlos Syndrome. Multiple factors contribute to the complexity of development of efficient algorithms for diagnostic testing. Limitations in diagnostic sensitivity and specificity of screening tests, diagnostic tests, and esoteric tests further compound the complexity of establishing a diagnosis. Educational efforts focusing on clinician awareness of RBDs and available testing options are vital for optimal management of such patients.

Harmonizing platelet function analyzer testing and reporting in a large laboratory network

INTRODUCTION

The platelet function analyzer (PFA) is a popular platelet function screening instrument, highly sensitive to von Willebrand disease (VWD) and to aspirin therapy, with moderate sensitivity to defects in platelet function and/or deficiencies in platelet number. There are two models, the original PFA-100 and the contemporary PFA-200. Normal reference ranges (NRRs) provided by the manufacturer are the same for both models, instead being based on the type of test cartridge, for which there are two main ones: collagen/epinephrine (C/Epi) and collagen/adenosine diphosphate (C/ADP).

METHODS

Comparative evaluations of PFA testing and reporting in six different sites of a large pathology network, aiming to harmonize NRRs and test reporting across all network sites. A separate comparative study of testing a range of samples (n > 150) on a PFA-100 versus that on a PFA-200. Review of contemporary literature.

RESULTS

Each site was identified to have a different reporting NRR, which after consolidating data permitted establishment of an agreed harmonized NRR for use across the network (C/Epi: 90-160; C/ADP: 70-124; based on n > 180). Similarly, each site reported and interpreted results in different ways, and after discussion and consolidation, a harmonized approach to interpretation and reporting was achieved. The separate comparative study of PFA-100 versus PFA-200 testing confirmed instrument equivalence.

CONCLUSION

We achieved harmonized NRRs and reporting for PFA testing across a large pathology network. Our approach may be useful for other laboratory networks wishing to harmonize PFA testing.

Utility of the Platelet Function Analyzer in Patients with Suspected Platelet Function Disorders: Diagnostic Accuracy Study

Introduction  The platelet function analyzer (PFA) is widely used as a screening tool for bleeding disorders in various settings. The diagnostic performance regarding platelet function disorders (PFDs), which are among the most common inherited bleeding disorders, is however still elusive. We aimed to assess the diagnostic value of PFA for PFD in clinical practice.

Methods  Comprehensive clinical and laboratory data of all consecutive patients referred to a specialized outpatient between January 2012 and March 2017 with a suspected bleeding disorder were prospectively recorded. The diagnostic work-up was performed according to a prespecified protocol following current guidelines and platelet function was tested using light transmission aggregometry as well as flow cytometry.

Results  Five hundred and fifty-five patients were included (median age 43.7 years; interquartile range [IQR] 29.3, 61.7; 66.9% female). Possible PFD was diagnosed in 64 patients (11.5%) and confirmed PFD in 54 patients (9.7%). In patients with confirmed PFD, median closure times were 107 seconds (ADP or adenosine diphosphate; IQR 89, 130) and 169 seconds (EPI; IQR 121, 211). In patients without bleeding disorders, PFA closure times were 96 seconds (ADP; IQR 83, 109) and 137 seconds (EPI; IQR 116, 158). The sensitivity was 19.5% in case of PFA ADP (95%CI 12.6, 30.0; specificity 86.4%; 95% CI 82.4, 89.8), and 44.3% in case of PFA EPI (95% CI 34.9, 53.9; specificity 75.6%; 95% CI 70.8, 79.9).

Conclusion  The diagnostic performance of PFA for PFD was moderate to poor. Our results do not support the utilization of PFA for screening of PFD in clinical practice.

A novel missense variant in the RASGRP2 gene in patients with moderate to severe bleeding disorder

Inherited platelet function disorder-18 (IPD-18) is a relatively new non-syndromic autosomal recessive bleeding disorder. It is characterized by deficient or dysfunctional CalDAG-GEFI protein. The distinctive feature of the disease is impaired platelet aggregation in response to multiple physiologic agonists. We here report a family with a platelet-type bleeding disorder and a novel mutation in the RASGRP2 gene. The overall bleeding score for the affected individuals was 15 and 12. Based on the initial diagnosis of Glanzmann thrombasthenia, targeted sequencing of integrin subunit alpha 2b and integrin subunit beta 3 encoding genes ITGA2B and ITGB3 were carried out in both affected members of a family. Sequence alignment failed to identify the disease-causing variant(s) in both genes. Therefore, whole exome sequencing in one affected individual was performed. Data analysis detected a novel homozygous missense variant (c.956C>T; p.Pro319Leu) in the exon 9 of the RASGRP2 gene. Five additional individuals of a family including both parents, an affected individual and two asymptomatic individuals were Sanger sequenced for the variant (c.956C>T). The variant segregates in the family in an autosomal recessive manner. Several in silico tools predicted the variant as pathogenic. Protein modeling studies suggest that the mutation (p.Pro319Leu) cause a conformational change in the loop structure of the RasGEF domain of the CalDAG-GEFI protein. Reported variants in the RasGEF domain impair expression and/or nucleotide exchange activity of CalDAG-GEFI protein and thus inhibit the activation of Rap1 protein required for platelet adhesion and hemostatic plug formation.

High Residual Platelet Reactivity during Aspirin Therapy in Patients with Non-St Segment Elevation Acute Coronary Syndrome: Comparison Between Initial and Late Phases

Background

High platelet reactivity (HPR) during therapy with acetylsalicylic acid (ASA) is a poor prognostic factor in acute coronary syndromes (ACS). The prevalence of HPR during ACS is greater than that reported in stable diseases. However, it is unclear whether this prevalence of HPR is a transient phenomenon or a characteristic of this high-risk population.

Objective

The main objective is to compare the effects of ASA on platelet function in the initial and late phases of ACS in a single population. Secondary objectives are: correlation between the tests between themselves and the relationship between the tests and the variation of the inflammatory markers (C-reactive protein and interleukin-6).

Methods

Seventy patients with non-ST segment elevation (NSTE) ACS in use of 100-200 mg of ASA per day for at least 7 days were prospectively studied. Platelet function was assessed in the first 48 hours and subsequently after 3 months using four methods: VerifyNow™ (VFN), whole blood platelet aggregation (WBPA) with arachidonic acid (AA) and collagen as agonists, and platelet function analyzer (PFA). The level of statistical significance considered was < 0.05.

Results

According to the more specific methods (WBPA with AA and VFN), the incidence of HPR was significantly higher in the early phase than in the late phase: WBPA with AA: 31% versus 13%, p = 0.015; VFN: 32% versus 16%, p = 0.049. The other methods tested, which were less specific for ASA, did not show significant differences between phases. The correlation between the methods was weak or moderate (r ranging from 0.3 to 0.5, p < 0.05), and there were no significant associations between HPR and inflammatory markers.

Conclusion

The prevalence of HPR during AAS therapy, assessed by specific methods for cyclooxygenase 1 (COX-1), is higher during the acute phase than in the late phase of NSTE ACS.

Both Granulocytic and Non-Granulocytic Blood Cells Are Affected in Patients with Severe Congenital Neutropenia and Their Non-Neutropenic Family Members: An Evaluation of Morphology, Function, and Cell Death

Objective:

To examine granulocytic and non-granulocytic cells in children with severe congenital neutropenia (SCN) and their non-neutropenic parents.

Materials and Methods:

Fifteen patients with SCN and 21 non-neutropenic parents were evaluated for a) CD95, CD95 ligand, annexin V, propidium iodide, cell cycle, and lymphocyte subsets by flow cytometry; b) rapid cell senescence (of leukocytes) by senescence-associated β-galactosidase stain; c) aggregation tests by aggregometer; d) in vitro bleeding time by PFA-100 instrument; e) mepacrine-labeled dense granule number of thrombocytes by fluorescence microscope; and f) hematomorphology by light and electron microscope. HAX1, ELANE, G6PC3, CSF3R, and JAGN1 mutations associated with SCN were studied in patients and several parents.

Results:

Significant increase in apoptosis and secondary necrosis in monocytes, lymphocytes, and granulocytes of the patients and parents was detected, irrespective of the mutation type. CD95 and CD95 ligand results implied that apoptosis was non-CD95-mediated. Leukocytes of 25%, 12.5%, and 0% of patients, parents, and controls showed rapid cell senescence. The cell cycle analysis testable in four cases showed G1 arrest and apoptosis in lymphocytes of three. The patients had HAX1 (n=6), ELANE (n=2), G6PC3 (n=2), and unidentified (n=5) mutations. The CD3, CD4, and NK lymphocytes were below normal levels in 16.6%, 8.3%, and 36.4% of the patients and in 0%, 0%, and 15.4% of the parents (controls: 0%, 0%, 5.6%). The thrombocytes aggregated at low rates, dense granule number/thrombocyte ratio was low, and in vitro bleeding time was prolonged in 37.5%-66.6% of patients and 33.3%-63.2% of parents (vs. 0% in controls). Under electron and/or light microscope, the neutrophils, monocytes, lymphocytes, and thrombocytes in the peripheral blood of both patients and parents were dysplastic and the bone marrow of patients revealed increased phagocytic activity, dysmegakaryopoiesis, and necrotic and apoptotic cells. Ultrastructurally, thrombocyte adhesion, aggregation, and release were inadequate.

Conclusion:

In cases of SCN, patients’ pluripotent hematopoietic stem cells and their non-neutropenic parents are both affected irrespective of the genetic defect.

Short-Term Hemostatic Safety of Strontium Ranelate Treatment in Elderly Women with Osteoporosis

Background:

Strontium ranelate offers significant clinical benefits in terms of efficacy, tolerability, and ease of administration in the treatment of postmenopausal osteoporosis. However, there are some data revealing an association between strontium ranelate treatment and increased incidence of venous thromboembolism (VTE), suggesting possible adverse prothrombotic effects of the drug.

Objective:

To assess the effect of strontium ranelate treatment on primary hemostasis, secondary hemostasis, and the natural anticoagulant defense system, together with prothrombotic markers, in elderly women with osteoporosis.

Methods:

This study was designed in a prospective manner. Thirty-five elderly women diagnosed with osteoporosis were included. During a 2 month treatment period, participants received strontium ranelate 2 g. Platelet Function Analyzer-100 (PFA-100) in vitro bleeding time was performed to depict primary hemostasis. Secondary hemostatic parameters including prothrombin time, international normalized ratio, activated partial thromboplastin time, anti-cardiolipine immunoglobulin (Ig) M and IgG, antiphospholipid IgM and IgG, protein C, protein S, anti-thrombin III, lupus anticoagulant, fibrinogen, thrombin, activated protein C resistance, and plasma levels of d-dimer were assessed. These parameters were tested before and after 2 month treatment with strontium ranelate.

Results:

Mean ± SD age of the patients was 72.82 ± 5.69 years. After 60 days of treatment, there was no statistically significant prolongation in PFA-100 in vitro bleeding time and no statistically significant change in the critical hemostatic parameters in patients receiving strontium ranelate that led to discontinuation of the treatment. None of the subjects developed clinical VTE during the 2 month period of strontium ranelate treatment.

Conclusions:

The hemostatic safety of strontium ranelate in the elderly population with osteoporosis was shown over 2 months of treatment; however, its long-term hemostatic safety should be evaluated further.

New Insights Into the Treatment of Glanzmann Thrombasthenia

Glanzmann thrombasthenia (GT) is a rare inherited autosomal recessive bleeding disorder of platelet function caused by a quantitative or qualitative defect of platelet membrane glycoprotein IIb/IIIa (integrin αIIbβ3), a fibrinogen receptor required for platelet aggregation. Bleeds in GT are variable and may be severe and unpredictable. Bleeding not responsive to local and adjunctive measures, as well as surgical procedures, is treated with platelets, recombinant activated factor VII (rFVIIa), or antifibrinolytics, alone or in combination. Although platelets are the standard treatment for GT, their use is associated with the risk of blood-borne infection transmission and may also cause the development of platelet antibodies (to human leukocyte antigens and/or αIIbβ3), potentially resulting in platelet refractoriness. Currently, where rFVIIa is approved for use in GT, this is mostly for patients with platelet antibodies and/or a history of platelet refractoriness. However, data from the prospective Glanzmann's Thrombasthenia Registry (829 bleeds and 206 procedures in 218 GT patients) show that rFVIIa was frequently used in nonsurgical and surgical bleeds, with high efficacy rates, irrespective of platelet antibodies/refractoriness status. The mechanisms underpinning rFVIIa effectiveness in GT have been studied. At therapeutic concentrations, rFVIIa binds to activated platelets and directly activates FX to FXa, resulting in a burst of thrombin generation. Thrombin converts fibrinogen to fibrin and also enhances GT platelet adhesion and aggregation mediated by the newly converted (polymeric) fibrin, leading to primary hemostasis at the wound site. In addition, thrombin improves the final clot structure and activates thrombin-activatable fibrinolysis inhibitor to decrease clot lysis.

Effects of increased von Willebrand factor levels on primary hemostasis in thrombocytopenic patients with liver cirrhosis

In patients with liver cirrhosis procoagulant and anticoagulant changes occur simultaneously. During primary hemostasis, platelets adhere to subendothelial structures, via von Willebrand factor (vWF). We aimed to investigate the influence of vWF on primary hemostasis in patients with liver cirrhosis. Therefore we assessed in-vitro bleeding time as marker of primary hemostasis in cirrhotic patients, measuring the Platelet Function Analyzer (PFA-100) closure times with collagen and epinephrine (Col-Epi, upper limit of normal ≤ 165 s) or collagen and ADP (Col-ADP, upper limit of normal ≤ 118 s). If Col-Epi and Col-ADP were prolonged, the PFA-100 was considered to be pathological. Effects of vWF on primary hemostasis in thrombocytopenic patients were analyzed and plasma vWF levels were modified by adding recombinant vWF or anti-vWF antibody. Of the 72 included cirrhotic patients, 32 (44.4%) showed a pathological result for the PFA-100. They had mean closure times (± SD) of 180 ± 62 s with Col-Epi and 160 ± 70 s with Col-ADP. Multivariate analysis revealed that hematocrit (P = 0.027) and vWF-antigen levels (P = 0.010) are the predictors of a pathological PFA-100 test in cirrhotic patients. In 21.4% of cirrhotic patients with platelet count ≥ 150/nL and hematocrit ≥ 27.0%, pathological PFA-100 results were found. In thrombocytopenic (< 150/nL) patients with cirrhosis, normal PFA-100 results were associated with higher vWF-antigen levels (462.3 ± 235.9% vs. 338.7 ± 151.6%, P = 0.021). These results were confirmed by multivariate analysis in these patients as well as by adding recombinant vWF or polyclonal anti-vWF antibody that significantly shortened or prolonged closure times, respectively. In conclusion, primary hemostasis is impaired in cirrhotic patients. The effect of reduced platelet count in cirrhotic patients can at least be partly compensated by increased vWF levels. Recombinant vWF could be an alternative to platelet transfusions in the future.

Emerging new trends in neurosurgical technologies

There has been tremendous progress in the modern day technologies causing a rapid evolution in the field of neurosurgery. The neurosurgeons have been equipped with the latest advancements such as the use of robotics in surgery, the image-guided neurosurgical procedures, and the stereotactic neurosurgery. In addition, the preoperative screening techniques have drastically improved the success of the surgical procedure. Neuronavigation has allowed the precise localization of the deep-seated brain structures thereby helping in the accurate operation of the affected regions without stirring the normal brain tissues. Such preciseness has helped in the improvement of the patient outcome. All these aspects have been discussed in detail in this review with a focus on their developmental background.

The Prevalence of von Willebrand Disease and Significance of in Vitro Bleeding Time (PFA-100) in von Willebrand Disease Screening in the İzmir Region

Objective: von Willebrand disease (vWD) is the most common hereditary bleeding disorder. The purpose of this investigation was to determine the prevalence of vWD among adolescents in İzmir and to assess the sensitivity and specificity of PFA-100 as a screening method in detecting this disease.

Material and Methods: Our study was conducted on adolescents in the city of İzmir between October 2006 and March 2007. A total of approximately 1500 high school students between 14 and 19 years of age were planned to be included in the investigation. Survey forms prepared for assessing hemorrhagic diathesis were completed by 1339 individuals (512 males, 827 females). The necessary laboratory tests were performed after having obtained written informed consent from 40 individuals suspected to have hemorrhagic diathesis.

Results: Based on the von Willebrand factor antigen (vWF:Ag) and ristocetin cofactor activity (vWF:RCo) levels and bleeding symptoms, vWD type-1 was diagnosed in 14 individuals (4 males, 10 females; prevalence: 1.04%). The most common bleeding symptom in these patients was found to be epistaxis (10/14). Screening with PFA-100 revealed prolongation in both cartridges (Col/ADP and Col/Epi) in 3 of the 14 patients. PFA-100 was determined to exhibit 21.4% sensitivity and 100% specificity in the diagnosis of vWD.

Conclusion: The PFA-100 device was found to have high specificity but to have exhibited low sensitivity. Therefore, its utilization as a screening test may be problematic in patients with mild type-1 vWD. Specific tests (vWF:RCo, vWF:Ag) are required for the definite diagnosis of vWD. However, further studies with a large number of patients are needed.

Conflict of interest:None declared.

The Platelet Function Analyzer (PFA-100) as a Screening Tool in Neurosurgery

We investigated whether the inclusion of the PFA-100 in the preoperative screening of neurosurgical patients might reduce perioperative bleeding complications. Patients with intracranial space-occupying lesions who were scheduled for neurosurgery underwent routine preoperative PFA-100 testing. In case of an abnormal PFA test, patients received prophylactic treatment with desmopressin. 93 consecutive patients were compared to 102 consecutive patients with comparable characteristics operated before introduction of the PFA-100 testing. 2 patients (2.2%) in the PFA group and 2 patients (2.0%) in the non-PFA group experienced clinically relevant intracranial bleeding confirmed by computed tomography (OR 1.05, 95% CI 0.39–2.82; P = 1.0). Transfusions were not significantly different between the two groups. 13 (14.0%) patients in the PFA group and 5 (4.9%) patients in the non-PFA group received desmopressin (OR 3.2, 95% CI 1.1–9.2; P = 0.045). Preoperative screening with the PFA-100 did result in a significant increase in the administration of desmopressin, which could not reduce perioperative bleeding complications or transfusions.

Diagnostic performance of the platelet function analyzer (PFA-100®) for the detection of disorders of primary haemostasis in patients with a bleeding history–a systematic review and meta-analysis

The Platelet Function Analyzer (PFA-100) is increasingly being used in the workup of patients with a bleeding diathesis. A profound knowledge of the possible diagnostic performance of this test is essential in order to make sound clinical decisions based on its results. It was the aim of this study to systematically review the published literature and provide valid estimates of the diagnostic performance of the PFA-100 for detecting disorders of primary haemostasis in newly presenting patients with a bleeding diathesis. A comprehensive literature search was performed for studies published between January 1994 and February 2006. Studies were eligible for the systematic review if they provided data supposed to be applicable to the determination of the diagnostic performance of the PFA-100. Furthermore, they were included in a meta-analysis if study reporting allowed calculation of sensitivity and specificity and if study quality ensured minimized biases of these estimates for the described clinical setting. Pooled weighted sensitivity, specificity and diagnostic odds ratio were calculated applying random effects modelling and constructing summary operator characteristic curves. This was done separately for the available test modifications using either collagen/epinephrine (PFA-EPI) or collagen/adenosine-diphosphate (PFA-ADP) for platelet activation. Thirty-six articles were included in the systematic review. Six studies met our eligibility criteria for a meta-analysis. The major reason for exclusion from the meta-analysis was a case-control design. A total of 1486 and 1259 patients were included in the meta-analysis of the diagnostic performance of the PFA-EPI and PFA-ADP, respectively. Pooled weighted sensitivity and specificity of the PFA-EPI/PFA-ADP in detecting a disorder of primary haemostasis were: 82.5/66.9% (95%-confidence interval (95%-CI): 76.0-88.9%/57.9-75.9%), and 88.7/85.5% (95%-CI: 84.3-93.1%/82.0-89.1%). 83/75% of patients with a positive PFA-EPI/PFA-ADP result do have a disorder of primary haemostasis whereas 88/79% with a negative PFA-EPI/PFA-ADP result do not. The PFA-EPI appeared to have a higher sensitivity and better predictive values than the PFA-ADP in detecting disorders of primary haemostasis, although a rigorous gold standard definition for a disorder of primary haemostasis, particularly for platelet disorders, was not applied in most studies. The majority of the studies lacked important requirements for quality and reporting, precluding a more precise and definitive characterization of the clinical utility of the PFA-100. This emphasizes the need for an evidence-based critical appraisal of diagnostic studies in haemostasis research in order to promote the conducting of studies that produce clinically relevant results.

Congenital dysgranulopoietic neutropenia

We investigated a 15-year-old female with congenital dysgranulopoietic neutropenia (CDN) and her non-neutropenic mother who had recurrent stomatitis. In both patients, cells of the neutrophilic, eosinophilic, monocytic, megakaryocytic, and basophilic series were dysmorphic. Plasmacytoid lymphocytes and mild megaloblastic erythroid precursors were present. Bleeding times of both patients were prolonged. The mother had a secondary aggregation defect; the number of the plasmacytoid lymphocytes, dense granules of platelets, and dysmorphic neutrophils, neutrophil chemotaxis, and myeloperoxidase content fluctuated according to the presence or not of aphthae. The daughter's karyotype revealed 46,XX/46,XX, t(1;8). No ELA2 or G-CSFR mutation was detected. These findings support stem cell involvement in CDN.

Laboratory Evaluation of Platelet Function

Platelets play a central role in hemostasis. Consequently, they lie at the heart of many inherited and acquired bleeding disorders and thrombotic events. The diagnosis of these disorders and monitoring of antiplatelet therapy require a thorough understanding of tests that measure platelet quantity and function. This article outlines basic concepts of platelet physiology and describes the tests that are commonly used in the clinical assessment of platelet function.

A review of inherited platelet disorders with guidelines for their management on behalf of the UKHCDO

The inherited platelet disorders are an uncommon cause of symptomatic bleeding. They may be difficult to diagnose (and are likely to be under-diagnosed) and pose problems in management. This review discusses the inherited platelet disorders summarising the current state of the art with respect to investigation and diagnosis and suggests how to manage bleeding manifestations with particular attention to surgical interventions and the management of pregnancy.

Glanzmann thrombasthenia

Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding syndrome affecting the megakaryocyte lineage and characterized by lack of platelet aggregation. The molecular basis is linked to quantitative and/or qualitative abnormalities of alphaIIb beta3 integrin. This receptor mediates the binding of adhesive proteins that attach aggregating platelets and ensure thrombus formation at sites of injury in blood vessels. GT is associated with clinical variability: some patients have only minimal bruising while others have frequent, severe and potentially fatal hemorrhages. The site of bleeding in GT is clearly defined: purpura, epistaxis, gingival hemorrhage, and menorrhagia are nearly constant features; gastrointestinal bleeding and hematuria are less common. In most cases, bleeding symptoms manifest rapidly after birth, even if GT is occasionally only diagnosed in later life. Diagnosis should be suspected in patients with mucocutaneous bleeding with absent platelet aggregation in response to all physiologic stimuli, and a normal platelet count and morphology. Platelet alphaIIb beta3 deficiency or nonfunction should always be confirmed, for example by flow cytometry. In order to avoid platelet alloimmunisation, therapeutic management must include, if possible, local hemostatic procedures and/or desmopressin (DDAVP) administration. Transfusion of HLA-compatible platelet concentrates may be necessary if these measures are ineffective, or to prevent bleeding during surgery. Administration of recombinant factor VIIa is an increasingly used therapeutic alternative. GT can be a severe hemorrhagic disease, however the prognosis is excellent with careful supportive care.

No alteration in the PFA-100 in vitro bleeding time induced by the Ginkgo biloba special extract, EGb 761, in elderly patients with mild cognitive impairment

EGb 761 is widely used in the management of mild cognitive impairment in the elderly population. Elucidation of the effects of EGb 761 on primary haemostasis via PFA-100 could represent an important step for better understanding of the haemostatic safety of EGb 761. The purpose of this prospective study is to assess the effects of Ginkgo biloba special extract, EGb 761, on PFA-100 in vitro bleeding time in elderly patients with mild cognitive impairment. A total of 40 elderly patients aged 65-79 years who were referred for geriatric assessment and who were diagnosed as having mild cognitive impairment were included. Patients were started on 80 mg EGb-761 three times daily. The complete set of PFA-100 in vitro bleeding time and coagulation parameters including prothrombin time, activated partial thromboplastin time and International Normalized Ratio were assessed before and on the seventh day of treatment with EGb 761. There was no statistically significant prolongation in PFA-100 in vitro bleeding time or coagulation parameters in patients receiving EGb 761 after 7 days. The data about the safety of EGb 761 from the point of primary haemostasis in our elderly patient population with mild cognitive impairment casts hope for the future management of this 'difficult-to-treat' population with the promising Ginkgo extracts.

Limited usefulness of the PFA-100 for the monitoring of ADP receptor antagonists--in vitro experience

We have evaluated the usefulness of the PFA-100 system (collagen/ADP and collagen/epinephrine cartridges) to assess the in vitro effects of a few platelet function inhibitors: Aspisol (60 microg/ml), 4-[4-[4-(aminoiminomethyl]-1-piperazinyl]-1-piperidineactetic acid, hydrochloride trihydrate (GR144053F, fibrinogen receptor antagonist, 100 nM), adenosine-3',5'-diphosphate (A3P5P, P2Y1 ADP receptor antagonist, 500 microM) and Bis[(adenosine-5'-O-phosphorodithioyl)methylene]-phosphinic acid (APTMPA, P2Y12 ADP receptor antagonist, 500 microM) on platelet function, as compared with the other commonly used diagnostic technique, a whole blood electrical aggregometry (20 microM ADP or 0.5 mM arachidonic acid). The in vitro studies were carried out on a group of 38 subjects. Whereas all the examined platelet antagonists and inhibitors almost completely blocked the 20 microM ADP- or 0.5 mM arachidonic acid-induced (in the case of acetylsalicylic acid) whole blood aggregation, only two inhibitors (Aspisol and GR144053F) remained effective in a significant prolongation of the PFA-100 occlusion time. Otherwise, using the PFA-100 system we were not able to detect the inhibitory actions of ADP receptor antagonists- P2Y1 and P2Y12. Our findings point to a limited usefulness of the PFA-100 system for the monitoring of the effectiveness of ADP receptor antagonists. The outcomes of this study show that platelet aggregometry in whole blood is characterised by the highest sensitivity in the monitoring of the investigated blood platelet inhibitors.

In vitro aspirin resistance detected by PFA-100 closure time: pivotal role of plasma von Willebrand factor

The in vitro closure time (CT), determined by the Platelet Function Analyzer (PFA-100), is used to monitor patients treated with aspirin. A relatively high percentage of in vitro aspirin resistance was reported despite an adequate inhibition of platelet response to arachidonic acid and we investigated whether high plasma levels of von Willebrand factor ristocetin cofactor activity (vWF:RCo) may contribute to this profile. Platelet aggregation test, CT [collagen adrenaline (CEPI-CT) and collagen adenosine 5'-diphosphate (ADP) (CADP-CT)], and vWF:RCo levels were evaluated in 55 consecutive patients receiving aspirin (75-250 mg/d) versus 32 untreated control subjects. All the aspirin-treated patients showed platelet aggregation responses that reflected the aspirin intake. However, CT data analysis enabled aspirin good-responder (GR) and aspirin bad-responder (BR) patients to be identified. All GR group subjects (n = 27), had a CEPI-CT and a CADP-CT longer than 300 s and 96 s respectively. The BR group (n = 28) had CEPI-CT values below 200 s and all CADP-CT were in the normal range (77 +/- 19 s). Interestingly, the BR plasma vWF:RCo levels were significantly higher (159 +/- 43%) than those of the GR group (121 +/- 34%) (P < 0.01), which were similar to control values (114 +/- 31%). A negative correlation between vWF:RCo and CT values was established. We demonstrate that in vitro aspirin-resistance, revealed by PFA-100 CT prolongation failure, is correlated to increased plasmatic vWF:RCo levels, reinforcing its particular importance in PFA-100 cartridges performance.