Comparison of PFA-100 and bleeding time testing in pediatric patients with suspected hemorrhagic problems

ISTH bleeding assessment tool and platelet function analyzer in children with mild inherited platelet function disorders

OBJECTIVES

To evaluate the diagnostic performance of platelet function analyzer (PFA) and The International Society on Thrombosis and Hemostasis bleeding-assessment-tool (ISTH-BAT) in detecting mild inherited platelet function disorders (IPFDs) in children with suspected bleeding disorders.

METHODS

Prospective single-center diagnostic study including consecutive patients <18 years with suspected bleeding disorder and performing a standardized workup for platelet function defects including ISTH-BAT, PFA, platelet aggregation testing, blood smear-based immunofluorescence, and next-generation sequencing-based genetic screening for IPFDs.

RESULTS

We studied 97 patients, of which 34 von Willebrand disease (VWD, 22 type-1, 11 type-2), 29 IPFDs (including delta-/alpha-storage pool disease, Glanzmann thrombasthenia, Hermansky-Pudlak syndrome) and 34 with no diagnosis. In a model combining PFA-adenosine diphosphate (ADP), PFA-epinephrine (EPI), and ISTH-BAT overall performance to diagnose IPFDs was low with area under the curves of 0.56 (95% CI 0.44, 0.69) compared with 0.84 (95% CI 0.76, 0.92) for VWD. Correlation of PFA-EPI/-ADP and ISTH-BAT was low with 0.25/0.39 Spearman's correlation coefficients. PFA were significantly prolonged in patients with VWD and Glanzmann thrombasthenia. ISTH-BAT-scores were only positive in severe bleeding disorders, but not in children with mild IPFDs or VWD.

CONCLUSION

Neither ISTH-BAT nor PFA or the combination of both help diagnosing mild IPFDs in children. PFA is suited to exclude severe IPFDs or VWD and is in this regard superior to ISTH-BAT in children.

Platelet abnormalities in patients with Parkinson's disease undergoing preoperative evaluation for deep brain stimulation

Normal hemostatic function is important for reduction of the risk of intracranial hemorrhage during stereotactic neurosurgery including deep brain stimulation (DBS) surgery. This study investigates the hemostatic function in patients with Parkinson’s disease (PD) undergoing preoperative evaluation for DBS, with emphasis on the number and function of platelets. In 107 PD patients, only one had abnormal activated partial prothrombin time and normal prothrombin time. Among the other 106 patients, six (5.7%) had only thrombocytopenia, seven (6.6%) only prolonged bleeding time (BT), and 14 (13.2%) only prolonged closure time (CT) of platelet function analyzer 100 (PFA-100). Totally, 34 of the 106 patients (32.1%) had at least one of three kinds of platelet abnormalities. No factor was found to be associated with the occurrence of platelet abnormalities except that abnormal platelet group and prolonged BT subgroup had more patients using selegiline and lower UPDRS-III motor subscore with medication off than normal platelet group (p < 0.05). The use of selegiline was significantly correlated with prolonged BT (p = 0.0041) and platelet abnormality (p = 0.0197). Therefore, it is important to have detailed evaluation of the hemostatic function for PD patients undergoing preoperative evaluation for DBS, especially the platelet number and function.

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.

Developmental Hemostasis: The Evolution of our Coagulation System

Developmental hemostasis describes the evolution of the coagulation system from the neonatal period through adulthood. Neonates have lower levels of coagulation factors and elevated screening levels at birth. These levels can be influenced by various circumstances including gestational age, labor effects, and clinical status. The most commonly used screening tests for coagulopathy are the prothrombin time, partial thromboplastin time, and fibrinogen level. These values can be difficult to interpret as every laboratory has its own age-specific reference ranges. An understanding of developmental hemostasis is important when evaluating, diagnosing, and treating clinical manifestations, including vitamin K deficiency, surgical needs, infections, inherited thrombophilias, and inherited bleeding disorders. The mainstay of treatment for bleeding or hemorrhage is platelet and fresh frozen plasma transfusions. For the treatment of thrombosis, unfractionated heparin and low-molecular-weight heparin are the 2 most commonly used anticoagulants in the neonatal setting.

Evaluation of a modified thromboelastography assay for the screening of von Willebrand disease

Thromboelastography (TEG) has been shown to be a valuable point-of-care device for the rapid diagnosis of various bleeding disorders. However, TEG has thus far not been used for the screening for von Willebrand disease (VWD). We evaluated the performance of a modified TEG assay for the laboratory screening of VWD. Three hundred twenty-eight patients (148 male, 180 female, median age 8.4 years, range 0.1 – 72.7 years) were included in the study. The diagnosis and classification of patients was based on personal and familial case history, von Willebrand factor antigen, ristocetin cofactor levels, collagen binding assay, factor VIII coagulant activity and multimer analysis. The ratio of clot strength after preincubation with ristocetin, and without ristocetin, represents the component of clot strength that is formed by cross-linked fibrin fibres and is dependent on the agglutinated platelet fraction. The decrease of the maximum amplitude is a function of the ristocetin concentration and provides a diagnostic parameter able to differentiate between healthy individuals and patients having VWD. Based on a preliminary cut-off value of 25% for the area under the curve (AUC) ratio, the sensitivity varied from 53% to 100% for the different VWD patient groups. The test is suitable for use as a screening test using whole blood and has the additional benefit of being suitable as a point of care test. It appears also useful for monitoring responses to desmopressin (DDAVP) and infusion therapy.

Ability of hemostatic assessment to detect bleeding disorders and to predict abnormal surgical blood loss in children: a systematic review and meta-analysis

BACKGROUND

Systematic preoperative coagulation testing is still widely used in children scheduled for surgery, although current guidelines recommend that a bleeding history should be the first choice for hemostatic assessment. We performed a systematic review with meta-analysis to evaluate the pertinence of bleeding questionnaire and screening laboratory testing to detect bleeding disorders (BDs) in children and to predict abnormal surgical blood loss.

METHODS

A search was conducted in PubMed, EMBASE, MEDLINE(R), Cochrane Central Register of Controlled Trials, Health technology Assessment, and all EBM Reviews (Cochrane DSR, ACP Journal Club, DARE, CCTR, CMR, HTA, and NHSEED and EBM Reviews) up to October 22, 2013. Prospective trials containing 20 children or more and any tests evaluating either the ability of the test to detect a congenital BD or the ability of the test to predict increased surgical blood loss were retained. The quality of the study was judged with the Cochrane Collaboration Tool and two investigators extracted data independently. Data were combined to calculate the pooled diagnostic odds ratio (DOR) and their 95% confidence intervals (CI 95%). I(2) statistics were used to assess statistics heterogeneity.

RESULTS

Data could be extracted from 16 studies. Best results for detecting a congenital abnormality at potential risk for increased surgical blood loss were obtained with the PFA-100 (DOR = 113.0; 95% CI, 22.6-566.2; I(2) = 0%) in two studies, followed by the bleeding time in two other studies (DOR = 110.7; 95% CI, 24.4-502.3; I(2) = 0%). With a high amount of heterogeneity, questionnaires showed disappointing performances (DOR = 7.9; 95% CI: 3.5-17.5; I(2) = 72.6%).

CONCLUSION

Current evidence does not identify a tool that adequately predicts BDs and/or abnormal surgical blood loss in children. Questionnaires currently available do not perform well. In the setting of a pediatric coagulation clinic, the PFA-100 has the highest chance of detecting a BD. This meta-analysis highlights the weakness of the literature regarding the prediction of perioperative bleeding due to congenital hemostatic disorders in children.

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 ® ) for evaluating primary hemostasis

The platelet-function analyzer, PFA-100, is a relatively novel method for rapid in vitro global evaluation of primary hemostasis. The aim of this review is to summarize the published studies reporting on the utility of the PFA-100 device as a screening tool for primary hemostasis. Data were identified by searches of the published literature, including PubMed, references from reviews and abstracts from the most important meetings on this topic. The literature data support the use of the PFA-100 as a useful screening tool for the investigation of von Willebrand's disease and other acquired and congenital intrinsic platelet function disorders. Moreover, it is useful for evaluating primary hemostasis before surgical procedures and for monitoring desmopressin therapy in both von Willebrand's disease and platelet function disorders. Given its high sensitivity, speed and simplicity of use, we conclude that the PFA-100 could replace the in vivo bleeding time as a screening test for primary hemostasis in routine clinical practice.

Pre-interventional haemostatic assessment: Guidelines from the French Society of Anaesthesia and Intensive Care

Recently the French Society of Anaesthesia and Intensive Care (Société Française d'Anesthésie et de Réanimation [SFAR]) issued recommendations for the prescription of routine preoperative testing before a surgical or non-surgical procedure, requiring any type of anaesthesia. Thirty clinical specialists performed a systematic analysis of the literature, and recommendations were then developed using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) system. One part of these guidelines is dedicated to haemostatic assessment. The goal of pre-anaesthetic screening for congenital or acquired haemostatic disorders is to prevent perioperative haemorrhagic complications through appropriate medical and surgical management. Preoperative assessment of bleeding risk requires a detailed patient interview to determine any personal or family history of haemorrhagic diathesis, and a physical examination is necessary in order to detect signs of coagulopathy. Laboratory investigation of haemostasis should be prescribed, not systematically, but depending on clinical evaluation and patient history. Standard tests (prothrombin time, activated partial thromboplastin time, platelet count) have a low positive predictive value for bleeding risk in the general population. Patients with no history of haemorrhagic diathesis and no conditions liable to interfere with haemostasis should not undergo pre-interventional haemostasis testing. Conversely, the existence of a positive history or a disease that could interfere with haemostasis should be an indication for clinically appropriate testing.

Making a diagnosis of VWD

A clear understanding of the molecular basis of VWD can guide the choice and interpretation of appropriate diagnostic tests. This review briefly describes the lifecycle and molecular interactions of VWF and how they lead to the current clinical classification. It also includes a brief discussion of the differential diagnosis and general workup of mucocutaneous bleeding, a review of the various VWD subtypes, and pertinent laboratory assays for each, including genetic tests. Finally, common testing pitfalls and diagnostic dilemmas are covered, including the challenge created by the overlap of borderline low VWF levels and mild bleeding.

The bleeding child. Part I: primary hemostatic disorders

Mucocutaneous bleeding is common in childhood and may be the result of primary hemostatic disorders such as vascular abnormalities, von Willebrand disease, thrombocytopenia, and platelet dysfunction. A detailed bleeding history and physical examination are essential to distinguish between normal and abnormal bleeding and to decide whether it is necessary to perform further laboratory evaluation. Initial laboratory tests include complete blood count, peripheral blood smear, mean platelet volume, von Willebrand factor (VWF) antigen assay, VWF ristocetin cofactor activity, and factor VIII activity. Once thrombocytopenia and von Willebrand disease have been excluded, platelet function should be tested by platelet aggregation. Additional specific diagnostic tests, such as platelet secretion tests and flow cytometry for the detection of platelet surface glycoprotein expression, are needed to confirm the raised hypothesis.

Making a diagnosis of VWD

A clear understanding of the molecular basis of VWD can guide the choice and interpretation of appropriate diagnostic tests. This review briefly describes the lifecycle and molecular interactions of VWF and how they lead to the current clinical classification. It also includes a brief discussion of the differential diagnosis and general workup of mucocutaneous bleeding, a review of the various VWD subtypes, and pertinent laboratory assays for each, including genetic tests. Finally, common testing pitfalls and diagnostic dilemmas are covered, including the challenge created by the overlap of borderline low VWF levels and mild bleeding.

Evidence-Based Principles in Pathology: Existing Problem Areas and the Development of “Quality” Practice Patterns

Context.—Contrary to the intuitive impressions of many pathologists, several areas exist in laboratory medicine where evidence-based medicine (EBM) principles are not applied. These include aspects of both anatomic and clinical pathology. Some non-EBM practices are perpetuated by clinical “consumers” of laboratory services because of inadequate education, habit, or overreliance on empirical factors. Other faulty procedures are driven by pathologists themselves.

Objectives.—To consider (1) several selected problem areas representing non-EBM practices in laboratory medicine; such examples include ideas and techniques that concern metastatic malignancies, “targeted” oncologic therapy, general laboratory testing and data utilization, evaluation of selected coagulation defects, administration of blood products, and analysis of hepatic iron-overload syndromes; and (2) EBM principles as methods for remediation of deficiencies in hospital pathology, and implements for the construction of “quality” practices in our specialty.

Data Sources.—Current English literature relating to evidence-based principles in pathology and laboratory medicine, as well as the authors' experience.

Conclusions.—Evidence-based medicine holds the promise of optimizing laboratory services to produce “quality” practices in pathology. It will also be a key to restraining the overall cost of health care.

Evaluation of children with a suspected bleeding disorder applying the Impact-R [Cone and Plate(let) Analyzer]

BACKGROUND

A convenient screening test for children with bleeding symptoms before more labor-intensive diagnostic steps are taken would be of value. The Impact-R was designed in an attempt to analyse platelet function under near physiological conditions. Results are presented as surface coverage (SC, %) and average size (AS, microm(2)).

OBJECTIVE

In this cross-sectional retrospective study, we assessed the use of the Impact-R in the evaluation of children with a suspected bleeding disorder (BD).

METHODS

The hospital charts of 110 children referred to the coagulation laboratory were reviewed for personal and family bleeding history (BH) as well as results of the laboratory evaluation.

RESULTS

A laboratory 'diagnosable' BD (LBD) was found in 23 children (21%, 95% CI 14-30%). A diagnosis of LBD was associated with the severity of bleeding but not with family BH. By receiver-operating characteristic (ROC) curve analysis, the SC was superior to the AS for diagnosis of a LBD. The Impact-R was abnormal in 43/97 children (44.3%, 95% CI 34-55%). The predictive values of a normal and abnormal Impact-R were 96% (95% CI 92-97%) and 42% (95% CI 28-56%), respectively. When considering the personal and family BH, the post-test probability for LBD after a normal Impact-R was reduced from 20% to 3.5% (95% CI 2.5-7%).

CONCLUSIONS

A normal Impact-R test is highly effective in excluding LBDs. Yet, in case of an abnormal Impact-R test, further testing is needed. An algorithm that includes the personal and family BH and the results of a screening test may improve the diagnostic process. Prospective studies are now needed to confirm these findings.

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.

[Evaluation of the haemostasis before a central block in children: what is the French anaesthesiologist's attitude?]

OBJECTIVE

Because of the lack of controlled studies, there is no consensus regarding the practice of routine haemostasis tests before neuraxial blockade in children. The purpose of this study was to describe the French surgical practice about the preoperative evaluation of coagulation in children who were scheduled for paediatric neuraxial anaesthesia.

STUDY DESIGN

Descriptive analysis of the practice.

METHODS

A telephone survey for coagulation screening was conducted in French surgical paediatric units, known to perform paediatric neuraxial anaesthesia on a routine basis. The aim of the standardized questionnaire was to evaluate the expertise in performance of neuraxial block, the modalities of the preoperative haemostasis screening, and the indications of biological tests and to assess whether a standardized team procedure was used.

RESULTS

Forty-two hospitals (27 universities, 10 general hospitals and five private institutions) were contacted; 61 anaesthesiologists with an expertise with central block answered the survey. Thirty-five institutions used a standardized procedure and 57,1% of them undertook routines tests only in children who are not walking. In the remaining 42,9%, the strategy was to screen systematically all patients whatever their age, familial and personal history as well as physical examination. However, only 54% of the anaesthesiologists performed an extensive physical examination in order to detect symptoms in favour of signs of haemostatic disorders.

CONCLUSION

While numerous data suggest that routine testing does not to provide much extra information in the absence of a positive history, a systematic strategy is still widely applied in children. Guidelines need to be developed to insure the safety of oriented tests.

Use of the platelet function analyzer to minimize bleeding complications after renal biopsy

BACKGROUND

The bleeding time is frequently used to screen primary haemostasis before surgical procedures, although it poorly predicts the risk of hemorrhage. The platelet function analyzer (PFA), which is also used to screen primary haemostasis, has a higher sensitivity and other advantages, like patient friendliness, higher degree of objectivity and analytical reliability, but needs more extensive clinical validation.

METHODS

We compared the predictive values of the PFA-CTs (closure times) and bleeding time for bleeding events after renal biopsy. We prospectively evaluated the complications in patients that underwent a renal biopsy and were screened with PFA in advance (n=170). For comparison we used a historical cohort of patients screened with the bleeding time (n=132).

RESULTS

When the PFA-CTs were normal, 26.0% of the patients had a mild bleeding event after the biopsy, which did not differ from the event rate with a normal bleeding time (29.4%). When one or both PFA-CTs were prolonged, 51.3% of the patients had post-biopsy bleeding events independently of the measures to correct the closure time(s), significantly more than with either a prolonged bleeding time (26.7%) or normal PFA-CTs (26.0%).

CONCLUSION

For bleeding events, the PFA has a higher positive and similar negative predictive value compared to the bleeding time. Taken into account the additional advantages of the PFA like patient friendliness and better analytical qualities, we prefer the PFA over the bleeding time as a screening tool for primary haemostasis before performing a renal biopsy.

The prevalence of bleeding disorders among healthy pediatric patients with abnormal preprocedural coagulation studies

BACKGROUND

We evaluated the prevalence of hemostatic disorders among pediatric patients with abnormal screening coagulation tests.

PROCEDURE

We analyzed 48 consecutive referrals for abnormal prothrombin times, partial thromboplastin times, or closure times obtained as preprocedural screens. Patients were evaluated by uniform diagnostic testing.

RESULTS

Seventeen patients (35%) had an isolated nonspecific inhibitor (NSI). Six patients (12.5%) presented with mildly low factor activity with a concomitant NSI. These deficiencies were of unclear clinical significance. One patient (2%) had a lupus anticoagulant. Only 9 patients (19%) had a possible or true mild bleeding disorder: 5 patients (10%) had isolated low von Willebrand factor levels, 2 patients (4%) had possible type I von Willebrand disease, and 2 (4%) had platelet aggregation disorders. In all patients, personal and family bleeding history had a positive predictive value of 45% for hemostatic disorders.

CONCLUSIONS

The most common diagnosis among the patients referred to us for abnormal preoperative coagulation tests was a NSI, which is not associated with an increased risk of operative bleeding complications. Less than 20% had a possible or true mild bleeding disorder. Although certain bleeding disorders can be occult in children and are associated with perioperative bleeding risks, our study demonstrates the inherent limitations in making a laboratory diagnosis of a bleeding disorder in pediatric patients preoperatively. Our findings contribute to existing doubt about the usefulness of prothrombin times, partial thromboplastin times, and closure times to identify occult bleeding disorders in this population.

Screening women with menorrhagia for underlying bleeding disorders: the utility of the platelet function analyser and bleeding time

Menorrhagia is a very common clinical problem among women of reproductive age and recent studies have suggested that underlying bleeding disorders, particularly von Willebrand's deficiency and platelet function defects, are prevalent in women presenting with menorrhagia. The objective of this study was to determine the utility of the platelet function analyser (PFA-100) and bleeding time (BT) as initial screening tests for underlying bleeding disorders in women with menorrhagia. In this study, 81 women with a physician diagnosis of menorrhagia underwent PFA-100 testing, BT and comprehensive haemostatic testing. The effectiveness of the PFA-100 and BT as screening tools in women with menorrhagia was assessed using results of haemostatic testing for von Willebrand's disease (VWD) and platelet dysfunction. In women presenting with menorrhagia, the PFA-100 had a sensitivity 80%, specificity 89%, positive predictive value (PPV) 33%, negative predictive value (NPV) 98% and efficiency 88% for VWD. For platelet aggregation defects, the PFA-100 closure time had a sensitivity 23%, specificity 92%, PPV of 75%, NPV of 52% and efficiency 55%. The data suggest that the PFA-100 may be useful in stratifying women with menorrhagia for further von Willebrand testing; however, neither the PFA-100 nor the BT tests are effective for purposes of classifying women for standard platelet aggregometry testing in women presenting with menorrhagia.

Minimizing perioperative blood loss and transfusions in children

PURPOSE

To summarize the physiology and pathophysiology relevant to perioperative blood loss in children. Strategies to reduce blood losses are reviewed.

METHODS

The literature was reviewed using the electronic library PUBMED and the Cochrane Database of Systematic Reviews. Relevant studies published in English or French with an English abstract are included. The following keywords were used: children, blood transfusion, surgical blood loss, erythropoietin, autologous blood, red blood cell saver, normovolemic hemodilution, desmopressin, aminocaproic acid, tranexamic acid, aprotinin, cardiac surgery, liver transplantation and scoliosis surgery.

MAIN FINDINGS

For patients with idiopathic scoliosis, predonation with or without the addition of erythropoietin is a safe and effective way to avoid the use of allogenic blood products. For open heart procedures: whole blood of less than 48 hr is helpful for children of less than two years of age undergoing complex procedures; tranexamic acid may be helpful for cyanotic heart disease and, to a lesser degree, for reoperations; while anti-kallikrein blood levels of aprotinin may both reduce the need for allogenic blood transfusions and improve postoperative oxygenation in infants.

CONCLUSION

Reducing perioperative allogenic blood transfusions is possible in pediatric patients provided that prophylactic measures are adapted to age, disease and type of surgery.

Bruising and bleeding in infants and children - a practical approach

Bruising and bleeding are commonly seen in children and are usually associated with minor injury and trauma. However, in two groups of children the bruising may be more significant than expected: those with an underlying haemostatic abnormality, such as an inherited bleeding disorder, or those who have been subjected to non-accidental injury (NAI). Diagnosing inherited bleeding disorders in children is fraught with difficulty, from venous access to interpretation of results; the possibility of NAI should be borne in mind, even in those children with proven significant bleeding disorders when the severity of the injury and the history are non-compatible. We describe the investigation of the haemostatic system in children with bruising and/or bleeding with emphasis on the key haemostatic disorders that need to be excluded.

Platelet function analyzer (PFA)-100 closure time in the evaluation of platelet disorders and platelet function

BACKGROUND

Closure time (CT), measured by platelet function analyzer (PFA-100) device, is now available to the clinical laboratory as a possible alternative or supplement to the bleeding time test.

AIM

On behalf of the Platelet Physiology Subcommittee of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (ISTH-SSC), a working Group was formed to review and make recommendations on the use of the PFA-100 CT in the evaluation of platelet function within the clinical laboratory.

METHODS

The Medline database was searched to review the published information on the PFA-100 CT in the evaluation of platelet disorders and platelet function. This information, and expert opinion, was used to prepare a report and generate consensus recommendations.

RESULTS

Although the PFA-100 CT is abnormal in some forms of platelet disorders, the test does not have sufficient sensitivity or specificity to be used as a screening tool for platelet disorders. A role of the PFA-100 CT in therapeutic monitoring of platelet function remains to be established.

CONCLUSIONS

The PFA-100 closure time should be considered optional in the evaluation of platelet disorders and function, and its use in therapeutic monitoring of platelet function is currently best restricted to research studies and prospective clinical trials.

Variables influencing Platelet Function Analyzer-100 closure times in healthy individuals

We investigated the relationship between platelet function analyzer (PFA-100) closure times (CT) and bleeding time (BT), platelet aggregation (PA) induced by ADP, arachidonic acid, and collagen, blood cell counts, and von Willebrand factor (VWF) in 120 well-characterised healthy individuals. Pre-analytical and analytical conditions were standardised comprehensively. In a substantial number of cases the differences between duplicate measurements exceeded 15%. The reference range (5th and 95th percentiles) for CT with the collagen/epinephrine (CEPI) and the collagen/ADP (CADP) cartridge was 93-223 s and 64-117 s respectively. Re-examination of 11 individuals with CEPI-CT above the 95th percentile revealed considerable batch-to-batch variation of CEPI-CT. Males had significantly longer CADP than females (P = 0.002). CEPI and CADP-CT measured pm were significantly longer than corresponding values determined am (P = 0.003 and P < 0.0001 respectively). Blood group O was associated with greater CEPI and CADP-CT and lower VWF levels compared with non-O blood groups (P = 0.008, P = 0.0003 and P < 0.0001 respectively). Linear regression analysis revealed association between CEPI-CT, CADP-CT and VWF (P < 0.0001), but no relationship was found between CT and BT or between CT and PA. We conclude that VWF plasma levels modulate PFA-100 CT to a greater extent than platelet function. Establishment of reliable reference ranges and careful standardisation of pre-analytical and analytical conditions is a prerequisite for obtaining reliable PFA-100 results. Duplicate measurements are necessary.

Mechanistic implications for the use and monitoring of recombinant activated factor VII in trauma

As interest in the use of activated recombinant factor VII (rFVIIa) in trauma grows, questions arise regarding how best to monitor rFVIIa therapy and when rFVIIa may be expected to improve hemostasis. Knowledge of the mechanisms of action may be combined with available data on laboratory monitoring and efficacy in various coagulopathic states in coming to clinically relevant conclusions. This review addresses the physiology of hemostasis, placing emphasis on how rFVIIa influences the process by both tissue factor dependent and tissue factor independent mechanisms. This is extended to a mechanistic consideration of how rFVIIa may function under acidotic, hypothermic, and hemodilutional and/or consumptive conditions of trauma related coagulopathy. When these considerations are viewed alongside the available clinical data, it becomes apparent that rFVIIa has potential to improve hemostasis during trauma coagulopathy, within limitations. Common laboratory procedures are discussed with reference to mechanisms of action of rFVIIa and the available clinical data. Although there is no single assay that can predict rFVIIa efficacy in trauma, the prothrombin time (PT) is recommended as a minimum. Although a shortened PT does not predict success, correction of PT into the normal range may be a better indicator. A nonresponding PT appears to indicate that rFVIIa alone will not lead to hemostasis, and that additional blood products and other measures must be applied. Once the patient is more stable, PT and thromboelastography are recommended.

The role of PFA-100R testing in the investigation and management of haemostatic defects in children and adults

The PFA-100 provides a simple global measure of high shear-dependent platelet function, and as such is not diagnostic or specific to any disorder. Prolonged closure times must be interpreted in conjunction with a full blood count, von Willebrand factor (VWF) screen and other platelet tests. The PFA-100 may also give false negative results with relatively common platelet defects. If clinical suspicion is high, further detailed platelet function testing and VWF screening are required to exclude abnormal platelet function, even if the PFA-100 is normal. In more recent studies the PFA-100 has been used for preoperative identification and management of surgical patients with haemostatic defects and for assessing the clinical effectiveness of platelet transfusion therapy. This review highlights the up to date, evidence-based, advantages and disadvantages of the PFA-100 test in the investigation and management of haemostatic disorders in both children and adults.

Evidence-based principles and practices in pathology: selected problem areas

Contrary to the intuitive impression of most pathologists, there are still many areas in laboratory medicine where evidence-based medicine (EBM) principles are not applied. These include aspects of both anatomic and clinical pathology. Some non-EBM practices are perpetuated by clinical "consumers" of laboratory services, because of inadequate education, habit, or over-reliance on empirical factors. Other faulty procedures are pathologist-driven, with similar underpinnings. This overview considers several exemplary problem areas representing non-EBM practices in the hospital laboratory. Such examples include ideas and techniques centering on metastatic malignancies, "targeted" oncological therapy, analysis of surgical margins in the excision of neoplasms, general laboratory testing and data utilization, evaluation of selected coagulation defects, administration of blood products, and analysis of hepatic iron-overload syndromes. The concepts illustrating departures from EBM are discussed for each of those topics.

Platelet function analysis

Since the last guidelines for BCSH platelet function testing were written in the late 1980s, many new tests have become available. Previously most platelet function tests were traditionally utilized to aid in the diagnosis and management of patients with platelet and haemostatic disorders. Most traditional tests were also largely restricted to the specialized laboratory or centre. However, nowadays there is also much renewed interest in monitoring the efficacy of anti-platelet therapy and measuring platelet hyper-function. A number of dedicated platelet function instruments have now become available that are much simpler to use and are beginning to be utilized as point of care instruments. These can now provide measurement of platelet function within whole blood without the requirement of sample processing. Some are also beginning to be incorporated into routine clinical use and can be utilized as not only as general screening tests of platelet function but to monitor anti-platelet therapy and to potentially assess both risk of bleeding and/or thrombosis. Modern flow cytometric-based platelet function analysis now also provides a wide variety of specific tests that can assess different aspects of platelet biology that are useful for diagnostic purposes. This review will highlight some of these of new tests/instruments and discuss their potential utility both within the haemostasis laboratory but also as potential point of care instruments.

Short- and long-term effects of therapy with interferon-alpha and pegylated interferon-alpha/ribavirin on platelet plug formation and von Willebrand factor release in patients with chronic hepatitis C

BACKGROUND

A pegylated interferon-alpha-induced decrease in platelet counts may become a limiting factor for continuation of therapy.

AIM

To evaluate the effect of pegylated interferon-alpha administration on platelet plug formation and von Willebrand factor antigen release in patients with chronic hepatitis C.

METHODS

Thirty patients with chronic hepatitis C (genotype 1; fibrosis 1-3: n = 16, cirrhosis: n = 14) received a single dose of 9 MU interferon-alpha2a, followed by weekly administration of 180 mug of pegylated interferon-alpha2a/ribavirin for 48 weeks. Platelet counts, platelet function (collagen-epinephrine-induced closure time) and von Willebrand factor antigen were measured.

RESULTS

Platelet counts and collagen-epinephrine-induced closure time decreased by 13% and 16%, respectively, 24 h after the first dose of interferon-alpha2a, and von Willebrand factor antigen levels increased by 31% (P < 0.01) compared with baseline. During a 48-week observation period, platelet counts decreased by a maximum of 33% (P < 0.001), von Willebrand factor antigen levels increased by 69% (P < 0.001) whereas collagen-epinephrine-induced closure time did not change. In noncirrhotic patients, the increase of von Willebrand factor antigen levels was maintained throughout therapy without a change in collagen-epinephrine-induced closure time. In contrast, in cirrhotics, von Willebrand factor antigen levels did not increase, while collagen-epinephrine-induced closure time was prolonged.

CONCLUSION

Single-dose interferon-alpha decreases platelet counts but improves platelet function, possibly by the release of von Willebrand factor antigen. Accordingly, long-term antiviral treatment had no effect on collagen-epinephrine-induced closure time, despite the decrease in platelet count in noncirrhotic patients. Such a compensation of decreased platelet counts by increased von Willebrand factor antigen level did not occur in cirrhotics.

Diagnosis and treatment of von Willebrand disease

Von Willebrand disease (VWD) is the most common bleeding disorder; it is believed to occur in approximately 1% to 2% of the population. Mucocutaneous and surgical hemorrhage in affected individuals is caused by quantitative and qualitative defects in von Willebrand factor (VWF), a large, multimeric protein that supports platelet adhesion and aggregation in the initiation of hemostasis at the time of vascular injury and functions as a carrier protein for factor VIII in the circulation. Advances in cellular and molecular biology have led to improved understanding of the pathophysiology of the disorder and development of a classification scheme that is based on quantitative and qualitative defects. Effective treatment is dependent on an accurate diagnosis using specific assays of VWF that define the various defects.

Non-accidental injury and the haematologist

In cases of suspected non-accidental injury in children, it is vital that a haematologist confirms the presence or absence of a haemostatic disorder so that the child welfare and legal systems can make accurate judgements regarding the cause of isolated injuries. The present paper will discuss commonly used methods for the diagnosis of coagulation disorders in children, and will describe how the investigation of easy bruising and bleeding can be highly problematic. For instance, some frequently used tests for the assessment of haemostasis in children are insensitive, inappropriate, or based on values derived from adult populations. Furthermore, artefact is a frequent problem, and many cases present with a negative family history of bleeding. Therefore, the role played by the haematologist in potential child abuse cases is an essential yet challenging one.

Platelet function in term and preterm neonates

Platelet dysfunction likely contributes to the pathophysiology of catastrophic hemorrhages in preterm neonates. In vitro studies have demonstrated that platelets of both term and preterm neonates are hyporesponsive to a variety of agonists. In contrast,template bleeding times of term neonates are shorter than those from adults. Very little is known about this and other tests of primary hemostasis in premature and sick neonates in the neonatal intensive care unit (NICU). This article covers the current knowledge of platelet function in preterm and term neonates and review show new agents (such as recombinant thrombopoietin and recombinant factor VIIa) may enhance neonatal platelet function.