Platelet function testing: Current practice among clinical centres in Northern Europe

Flow Cytometry and Platelets

Clinical assessment of platelet activation by flow cytometry is useful in the characterization and diagnosis of platelet-specific disorders and as a measure of risk for thrombosis or bleeding. Platelets circulate in a resting, "unactivated" state, but when activated they undergo alterations in surface glycoprotein function and/or expression level, exposure of granule membrane proteins, and exposure of procoagulant phospholipids. Flow cytometry provides the means to detect these changes and, unlike other platelet tests, is appropriate for measuring platelet function in samples from patients with low platelet counts. The present review will focus on flow cytometric tests for platelet activation markers.

Classic Light Transmission Platelet Aggregometry: Do We Still Need it?

For more than 50 years, light transmission aggregometry has been accepted as the gold standard test for diagnosing inherited platelet disorders in platelet-rich plasma, although there are other functional approaches performed in whole blood. In this article, several advantages and disadvantages of this technique over other laboratory approaches are discussed in the view of recent guidelines, and the necessity of functional assays, such as light transmission aggregometry in the era of molecular genetic testing, is highlighted.

Standardization of definition and management for bleeding disorder of unknown cause: communication from the SSC of the ISTH

In many patients referred with significant bleeding phenotype, laboratory testing fails to define any hemostatic abnormalities. Clinical practice with respect to diagnosis and management of this patient cohort poses significant clinical challenges. We recommend that bleeding history in these patients should be objectively assessed using the International Society on Thrombosis and Haemostasis (ISTH) bleeding assessment tool. Patients with increased bleeding assessment tool scores should progress to hemostasis laboratory testing. To diagnose bleeding disorder of unknown cause (BDUC), normal complete blood count, prothrombin time, activated partial thromboplastin time, thrombin time, von Willebrand factor antigen, von Willebrand factor function, coagulation factors VIII, IX, and XI, and platelet light transmission aggregometry should be the minimum laboratory assessment. In some laboratories, additional specialized hemostasis testing may be performed to identify other rare causes of bleeding. We recommend that patients with a significant bleeding phenotype but normal laboratory investigations should be registered with a diagnosis of BDUC in preference to other terminology. Global hemostatic tests and markers of fibrinolysis demonstrate variable abnormalities, and their clinical significance remains uncertain. Targeted genomic sequencing examining candidate hemostatic genes has a low diagnostic yield. Underlying BDUC should be considered in patients with heavy menstrual bleeding since delays in diagnosis often extend to many years and negatively impact quality of life. Treatment options for BDUC patients include tranexamic acid, desmopressin, and platelet transfusions.

Development of a Coagulation Disorders Unit

Our Coagulation Disorders Unit in Helsinki, Finland, provides 24/7 services for local and national hospitals and colleagues upon requests regarding bleeding and thrombosis diagnostics and management, including follow-up. The unit has a tight connection between the clinic and laboratory, and its maintenance and sharing knowledge and observations have been priorities, already for over 20 years and will continue to be of major importance. The consultation service is provided by phone during daytime and on-call hours, and in written form sent electronically to the consulting stakeholders. Thrombosis and hemostasis-targeted outpatient clinics are also available for the patients referred to the center. Writing local guidance and official guidelines, Nordic, European and international collaboration, and educational activities including social communication are critical elements for the Coagulation Disorders Unit. Alertness to acute coagulation abnormalities, such as occurred during COVID-19 and vaccine-induced thrombosis and thrombocytopenia, and development of strategies to manage cross-disciplinary problems are topics which call upon broad networking. The Nordic community has an ongoing historical meeting, which has been circulating among coagulation centers for the past 56 years. At the European level, the European Association of Haemophilia and Allied Disorders focuses on bleeding disorders and their management, including safety surveillance. The International Society of Thrombosis and Haemostasis offers excellent basic and clinical benchmarks for any Coagulation Disorders Unit. We hope that the description of the development and implementation of our Coagulation Disorders Unit in Helsinki achieves international interest and broadens international collaboration. Finally, we congratulate STH on its great contributions around the globe and for providing a vivid forum to foster the discipline of thrombosis and hemostasis.

Flow-chamber device (T-TAS) to diagnose patients suspected of platelet function defects

BACKGROUND

Patients suspected of platelet function defects represent a diagnostic challenge for the clinical laboratory, mainly due to the complexity and poor standardization of screening methods. We compared a new flow-based chip-equipped point-of-care (T-TAS) device with lumi-aggregometry and other specific tests.

MATERIALS AND METHODS

The study included 96 patients suspected of platelet function defects and 26 patients referred to hospital for an evaluation of residual platelet function while on antiplatelet therapy.

RESULTS

Forty-eight of 96 patients displayed abnormal platelet function by lumi-aggregometry, and 10 of them had defective granule content and were classified as δ-storage pool disease (δ-SPD). T-TAS compared favorably with lumi-aggregometry in detecting the most severe forms of platelet function defects (i.e., δ-SPD) [test agreement (lumi-light transmission aggregometry [lumi-LTA] vs T-TAS) for the δ-SPD subgroup was 80% and K CHOEN 0.695. T-TAS was less sensitive to milder platelet function defects (i.e., primary secretion defects [PSD]). Concerning patients on antiplatelets, test agreement (lumi-LTA vs T-TAS) in detecting patients who were responders to this therapy was 54%; K CHOEN 0.150.

DISCUSSION

The results indicate that T-TAS can detect the more severe forms of platelet function defects such as δ-SPD. There is limited agreement of T-TAS with lumi-aggregometry in identifying responders to antiplatelets. However, this poor agreement is commonly shared by lumi-aggregometry and other devices owing to the lack of test specificity and of prospective data from clinical trials linking platelet function with therapeutic efficacy.

Hematology and coagulation preanalytics for clinical chemists: Factors intrinsic to the sample and extrinsic to the patient

In hematology and coagulation, diligence in the preanalytical phase of testing is of critical importance to obtaining reliable test results. If the sample used for testing is unsuitable, even outstanding analytical procedures and technology cannot produce a clinically-reliable result. Therefore, the intent of this manuscript is to review preanalytical factors intrinsic to the sample that affect the hematology and coagulation testing. Factors intrinsic to the sample (excluding in vivo anomalies) can be controlled, theoretically, by phlebotomists (including nurses) and laboratorians in the preanalytical phase of testing. Furthermore, the management and prevention of such factors is highlighted. Erroneous control of preanalytical factors can produce laboratory errors.