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

Point-of-Care Testing in Patients with Hereditary Disorders of Primary Hemostasis: A Narrative Review

Inherited disorders of primary hemostasis, such as von Willebrand disease and congenital platelet disorders, can cause extensive, typically mucocutaneous bleeding. Assays to diagnose and monitor these disorders, such as von Willebrand factor activity assays and light transmission aggregometry, are performed in specialized hemostasis laboratories but are commonly not available in local hospitals. Due to the complexity and relative scarcity of these conventional assays, point-of-care tests (POCT) might be an attractive alternative in patients with hereditary bleeding disorders. POCTs, such as thromboelastography, are increasingly used to assess hemostasis in patients with acquired hemostatic defects, aiding clinical decision-making in critical situations, such as during surgery or childbirth. In comparison, the use of these assays in patients with hereditary hemostasis defects remains relatively unexplored. This review aims to give an overview of point-of-care hemostasis tests in patients with hereditary disorders of primary hemostasis. A summary of the literature reporting on the performance of currently available and experimental POCTs in these disorders is given, and the potential utility of the assays in various use scenarios is discussed. Altogether, the studies included in this review reveal that several POCTs are capable of identifying and monitoring severe defects in the primary hemostasis, while a POCT that can reliably detect milder defects of primary hemostasis is currently lacking. A better understanding of the strengths and limitations of POCTs in assessing hereditary defects of primary hemostasis is needed, after which these tests may become available for clinical practice, potentially targeting a large group of patients with milder defects of primary hemostasis.

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.

[Coagulation diagnostics in the clinical routine-Part 1 : Evaluation of the risk of bleeding before surgery, interventions and diagnostics in bleeding diathesis]

This article on coagulation diagnostics is published in two parts covering five common clinical scenarios for coagulation diagnostics. Part 1 deals with the diagnostics prior to invasive interventions and coagulation diagnostics to clarify a tendency to bleeding. The global parameters Quick and activated partial thromboplastin time are established for monitoring certain anticoagulants; however, they are not predictive with respect to the risk of bleeding prior to elective invasive interventions. In this context, disorders of primary hemostasis are frequent, which are insufficiently detected by the global parameters. Most clinical bleeding tendencies are due to acquired causes. These include anticoagulants and diseases which can be accompanied by tendency to bleeding. For coagulation tests preanalytical issues are essential in order to avoid false results. The interpretation should always be made in the context of the current physiological state.

Multiparameter platelet function analysis of bleeding patients with a prolonged platelet function analyser closure time

Patients referred for evaluation of bleeding symptoms occasionally have a prolonged platelet function analyser (PFA) closure time, without evidence for von Willebrand disease or impaired platelet aggregation. The aim of this study was to establish a shear‐dependent platelet function defect in these patients. Patients were included based on high bleeding score and prior PFA prolongation. Common tests of von Willebrand factor (VWF) and platelet function and exome sequencing were performed. Microfluidic analysis of shear‐dependent collagen‐induced whole‐blood thrombus formation was performed. In 14 PFA‐only patients, compared to healthy volunteers, microfluidic tests showed significantly lower platelet adhesion and thrombus formation parameters. This was accompanied by lower integrin activation, phosphatidylserine exposure and P‐selectin expression. Principal components analysis indicated VWF as primary explaining variable of PFA prolongation, whereas conventional platelet aggregation primarily explained the reduced thrombus parameters under shear. In five patients with severe microfluidic abnormalities, conventional platelet aggregation was in the lowest range of normal. No causal variants in Mendelian genes known to cause bleeding or platelet disorders were identified. Multiparameter assessment of whole‐blood thrombus formation under shear indicates single or combined effects of low–normal VWF and low–normal platelet aggregation in these patients, suggesting a shear‐dependent platelet function defect, not detected by static conventional haemostatic tests.

Laboratory characterization of obligate carriers of type 3 von Willebrand disease with a potential role for Platelet Function Analyzer (PFA-200)

INTRODUCTION

Type 3 von Willebrand disease (VWD) is a rare autosomal recessive disorder characterized by undetectable von Willebrand Antigen (VWF:Ag). Carriers of type 3 VWD carry one null allele and have von Willebrand factor (VWF) at about 50% of normal. The aim of this study was to characterize type 3 VWD carriers and to study the role of Platelet Function Analyzer (PFA-200) in this cohort.

METHODS

This was a cross-sectional study where data were collected from carriers (parents/offspring) of type 3 VWD patients and evaluated with activated partial thromboplastin time, factor VIII, blood group, ristocetin cofactor assay (VWF:RCo), VWF:Ag, and closure time on PFA-200 with collagen/epinephrine (COL/EPI), and collagen/ADP (COL/ADP).

RESULTS

One hundred carriers were included in the study of which 85 were included for PFA-200 analysis. The mean (SD) of VWF:Ag (IU/ml) and VWF:RCo (IU/ml) was 0.63 (0.24) and 0.61 (0.26), respectively. Among the 100 carriers, based on VWF levels (VWF:Ag and/or VWF:RCo) and bleeding history, there were 7 type 1 VWD, 10 type 2 VWD, 25 borderline VWF (0.30-0.50 IU/ml and no bleeding), and 58 normal VWF (>0.50 IU/ml). PFA-200 was prolonged in 71% of the carriers, all carriers with type 1 and type 2 VWD phenotype, 80% carriers with borderline VWF, and 59% with normal VWF. COL/EPI was more sensitive than COL/ADP and showed better correlation with VWF parameters than COL/ADP.

CONCLUSION

Carriers of type 3 VWD can have a variable laboratory phenotype. PFA-200 showed good sensitivity among the carriers at VWF levels <0.50 IU/ml.

Updates in diagnosis of the inherited platelet disorders

PURPOSE OF REVIEW

To provide a comprehensive update on the current available methodologies and techniques for diagnosis of inherited platelet disorders (IPD).

RECENT FINDINGS

The contributions of many groups have resulted in the significant progress in the molecular diagnosis of IPD including the identification of many genes responsible for the various phenotypes. The widespread use and availability of next-generation sequencing has brought to the forefront ethical challenges associated with nontargeted sequencing as well as provided us with novel variants to functionally validate. These requirements have driven the development of novel tools for functional assessment of platelets, although none of the novel techniques beyond sequencing have yet taken clinical hold.

SUMMARY

Much work is ongoing on functional and molecular assessment of platelet disorders and the incorporation of combined assessments is likely to yield the highest diagnostic results.

Inherited platelet disorders : Management of the bleeding risk

Inherited platelet disorders are rare bleeding syndromes due to either platelet function abnormalities or thrombocytopenia which may be associated with functional defects. The haemorrhagic symptoms observed in these patients are mostly muco-cutaneous and of highly variable severity. Although 30 to 50% of the platelet disorders are still of unknown origin, the precise diagnosis of these pathologies by specialized laboratories together with haemorrhagic scores enables an assessment of the risk of bleeding in each patient. Depending on the diagnostic elements collected, an appropriate medical procedure can be proposed for each situation: scheduled or emergency surgical interventions and pregnancy follow-up. The pathologies most at risk correspond to Glanzmann's thrombasthenia, Bernard-Soulier syndrome, severe thrombocytopenia (<40,000 platelets/μL) and signalling protein abnormalities affecting the activation of GPIIb-IIIa, a membrane glycoprotein essential for platelet aggregation. For these particular patients, in whom the risk of bleeding can be increased by a factor of 40, management protocols during surgical procedures are generally based on the use of conventional platelet concentrates, for both prophylaxis and the control of active bleeding. The perinatal period in women with platelet disorders and their new-born also require special attention. Indeed, beyond unpredictable delivery haemorrhages, bleeding requiring a blood transfusion is observed after delivery in more than 50% of women with Glanzmann's thrombastenia or Bernard-Soulier syndrome.

Population pharmacodynamics of cilostazol in healthy Korean subjects

Cilostazol is used for the treatment of intermittent claudication, ulceration and pain. This study was conducted to develop a population pharmacodynamic (PD) model for cilostazol's closure time (CT) prolongation effect in healthy Korean subjects based on a pharmacokinetic (PK) model previously developed. PD data were obtained from 29 healthy subjects who participated in a study conducted in 2009 at Severance Hospital. The PK model used was a two-compartment model with first order absorption. CT data were best described by a turnover model with a fractional turnover rate constant (K_out) inhibited by drug effects (Eff), which were represented by a sigmoid E_max model [Eff = E_max · C^γ / (EC₅₀^γ+Cγ)] with E_max being maximum drug effect, EC₅₀ drug plasma concentration at 50% of E_max, C drug plasma concentrations, and γ the Hill coefficient. For the selected PD model, parameter estimates were 0.613 hr⁻¹ for K_out, 0.192 for E_max, 730 ng/ml for EC₅₀ and 5.137 for γ. Sex and caffeine drinking status significantly influenced the baseline CT, which was 85.36 seconds in male non-caffeine drinkers and increased by 15.5% and 16.4% in females and caffeine drinkers, respectively. The model adequately described the time course of CT. This was the first population PD study for cilostazol's CT prolongation effect in a Korean population.

Platelet reactivity in thromboelastometry. Revision of the FIBTEM test: a basic study

This study aimed to investigate modifications to the FIBTEM test to better assess fibrinogen levels and the quality of fibrin polymerization in citrated blood using Multiplate impedance aggregometry to verify platelet inhibition. Blood samples from 26 healthy volunteers were subjected to thromboelastometry studies (EXTEM/FIBTEM tests) in accordance with the standard study protocol (cytochalasin D) and according to a modified protocol (synthetic IIbIIIa receptor antagonist vs. acetylsalicylic acid [ASA] + synthetic IIbIIIa receptor antagonist instead of cytochalasin D). Independent of thromboelastometry, Multiplate impedance aggregometry was used to assess the degree of restriction by the platelet blocked with the following treatments: (1) cytochalasin D, (2) synthetic IIbIIIa antagonist or (3) ASA + synthetic IIbIIIa antagonist to assess the aggregation response to activation with an agonist (ADP, collagen, thrombin receptor activating peptide-6 [TRAP-6], and arachidonic acid). Via aggregometry, cytochalasin D more weakly inhibited platelet aggregation than simultaneous administration of the -IIbIIIa receptor antagonist with ASA. However, total platelet aggregation inhibition was observed after simultaneous administration of cytochalasin D combined with a synthetic IIbIIIa receptor antagonist. In the thromboelastometry, a significant decrease of the A10, A20 and MCF parameters were observed in the EXTEM/FIBTEM tests after they were modified by the addition of a synthetic IIbIIIa receptor antagonist alone or in combination with ASA. In conclusion, in this Multiplate- and ROTEM-based laboratory approach, a two-way blockade (IIbIIIa-antagonist + cytochalasine D) was sufficient to completely inhibit procoagulant platelet function as observed by aggregometry and thromboelastometry.

Whole Blood Platelet Aggregometry

Light transmittance aggregometry is the historical reference method for platelet function testing and continues to be used extensively. Whole blood impedance lumiaggregometry represents an updated methodology that provides for simplified specimen management, an assay milieu that replicates in vivo platelet activation conditions, improved reproducibility, and near-patient testing. While the impedance-based whole blood aggregometer with luminescence channel is becoming the standard for platelet function testing using this methodology, at least three near-patient whole blood instruments are available, each employing its unique technology. We provide descriptions of whole blood lumiaggregometry and three near-patient systems. We include the principle of operation, materials, and stepwise example protocols and speculate on the importance of concordance among the platforms.

Platelet function testing: from routine to specialist testing

Platelets have many functions within the haemostatic system, and when these actions are diminished for whatever reason, a bleeding tendency can manifest. Unravelling the reason(s) for this bleeding can be complex due to the multiple roles platelets perform. This review seeks to explain each level of platelet testing moving from those performed at local hospital laboratories to those performed by specialist centres and university research departments. It will examine the testing available and discuss when to move on to additional testing.

Surgeon's guide to anticoagulant and antiplatelet medications part two: antiplatelet agents and perioperative management of long-term anticoagulation

An increasing number of potent antiplatelet and anticoagulant medications are being used for the long-term management of cardiac, cerebrovascular, and peripheral vascular conditions. Management of these medications in the perioperative and peri-injury settings can be challenging for surgeons, mandating an understanding of these agents and the risks and benefits of various management strategies. In this two part review, agents commonly encountered by surgeons in the perioperative and peri-injury settings are discussed and management strategies for patients on long-term antiplatelet and anticoagulant therapy reviewed. In part one, we review warfarin and the new direct oral anticoagulants. In part two, we review antiplatelet agents and assessment of platelet function and the perioperative management of long-term anticoagulation and antiplatelet therapy.

Effect of cocoa products and flavanols on platelet aggregation in humans: a systematic review

The percentage of healthy subjects with decreased platelet aggregation after bolus consumption of cocoa products is reported.

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.

Inherited disorders of platelet function

Inherited platelet function disorders are of variable severity and unknown frequency and may be difficult to diagnose. Nevertheless, they are increasingly recognized as an important cause of bleeding in pediatrics, particularly in adolescent girls with menorrhagia, where they may be more common than von Willebrand disease. This article reviews the presentation of these disorders, summarizes the most common types of platelet function disorders, discusses the challenges in diagnostic testing, and details treatment and supportive care options.

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.

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.

Pronounced platelet hyperfunction in patients with cardiac arrest achieving restoration of spontaneous circulation

OBJECTIVE

Markers of platelet activation are increased in patients undergoing cardiopulmonary resuscitation. Hyperfunctional platelets may contribute to impairment of microcirculatory function and overall poor outcome despite restoration of spontaneous circulation (ROSC). Patients with myocardial infarction have hyperfunctional platelets, which predict the degree of myocardial necrosis. Thus, we hypothesized that platelets may be even more activated in patients whose myocardial infarction leads to cardiac arrest and compared them with patients whose cardiac arrest was due to a noncardiac origin.

DESIGN

Prospective observational study.

SETTING

Emergency department of a tertiary care hospital.

PATIENTS

One hundred four patients with witnessed cardiac arrest who achieved ROSC.

INTERVENTIONS

Blood sampling.

MEASUREMENTS AND MAIN RESULTS

We assessed collagen adenosine diphosphate closure time with the platelet function analyzer-100, and measured plasma levels of von Willebrand factor: ristocetin cofactor activity levels by turbidometry. Independent physicians diagnosed the origin of cardiac arrest. The majority of cardiac arrests were caused by myocardial ischemia. Invariably, collagen adenosine diphosphate closure time values (55 seconds; 95% confidence interval: 52-58 seconds) were much shorter in these patients compared with patients with other causes of cardiac arrest (110 seconds; 95% confidence interval: 84-135 seconds, p < 0.001). von Willebrand factor: ristocetin cofactor activity plasma levels were more than three-fold above normal values in both groups.

CONCLUSIONS

Patients with myocardial ischemia-triggered cardiac arrest had the highest degree of platelet hyperfunction under high shear rates, which was not solely due to increased von Willebrand factor. Future trials are necessary to clarify whether rapid, more aggressive antiplatelet therapy improves outcome after cardiac arrest.

Surgery in patients with vascular malformations of the head and neck: value of coagulation disorders

Objectives

The surgical treatment of congenital vascular malformations always bears the risk of severe bleeding. The aim of this study was to investigate the prevalence of haemostatic abnormalities in patients with congenital vascular malformations of the head and neck which could additionally complicate the complex surgery of vascular malformations.

Methods

Thirteen patients with congenital vascular malformations of the head and neck, who underwent scheduled surgery, were reviewed regarding their haemostatic tests, including prothrombin time, activated partial thromboplastin time, fibrinogen level, platelet count, platelet function analyzer-epinephrine (PFA-Epi) and -adenosine diphosphate (ADP) (PFA-100®), von Willebrand factor (vWF) and D-dimers.

Results

In six of 13 patients an impaired primary haemostasis was detected by prolonged PFA-Epi and one of these patients also had a slightly prolonged PFA-ADP. Additionally, two of the patients showed mild coagulation factor deficiency. One patient had a mild vWF deficiency that was not detected by PFA-100®.

Conclusion

Prior to surgery of congenital vascular malformations of the head and neck, a detailed coagulation analysis is needed in order to identify those patients at increased risk of bleeding. This proceeding is supported by the fact that a relevant portion of the patients with congenital vascular malformations of the head and neck show an impaired primary haemostasis.

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.