Multicenter evaluation of light transmission platelet aggregation reagents: communication from the ISTH SSC Subcommittee on Platelet Physiology

Epidemiological and clinical characteristics of children and young adults with Glanzmann's thrombasthenia in upper Egypt: a multicenter cross-sectional study

BACKGROUND

Glanzmann's thrombasthenia (GT) is an inherited rare bleeding disorder characterized by a deficiency or functional defect in the platelet αIIbβ3 integrin. This impairs normal platelet aggregation and leads to prolonged and spontaneous mucocutaneous bleeds.

OBJECTIVES

To report disease characteristics of a GT cohort from five tertiary hospitals in Upper Egypt.

MATERIALS AND METHODS

We conducted a retrospective cross-sectional observational study, relying on patients' medical records and interview surveys to collect information from patients diagnosed with congenital GT between October 2023 and April 2024.

RESULTS

We recruited 131 people with GT (PwGT) of different ages, mainly children and adolescents. 73.3% of the study cohort had type I GT, 23.7% had type II GT, and 3% had type III GT. Consanguinity and family history were prevalent in our cohort, with an expected prevalence of more than one per 200,000 in our region. The median value of ADP aggregation was 8%. In type I GT, the median levels of CD41 and CD61 were 0.3%. In contrast, type II GT had median levels of 12% for CD41 and 17% for CD61. The most frequent manifestations were epistaxis (77.1%), subcutaneous bleeds (40.5%), menorrhagia (22.1%), and mucosal bleeds (18.3%). 72.5% of PwGT used rFVIIa and 69.5% used platelet transfusions to treat acute and surgical bleeds, while only 6.9% used tranexamic acid as monotherapy.

CONCLUSION

Estimating the actual burden of GT in Egypt requires accurate diagnoses, as well as systematic and standardized data collection. The rooted consanguinity pattern in Upper Egypt contributes to a higher prevalence of GT above the country's average.

Interindividual variability in platelet reactivity among individuals with or without antiplatelet therapy: results from a large tertiary care hospital

Antiplatelet therapy is crucial for reducing thrombotic events in patients with atherosclerotic disease, but the response vary widely among individuals. The identification of patients at high (HPR), optimal (OPR) or low platelet reactivity (LPR) is dependent on high interlaboratory variability. We report results of a large dataset of patients to assess the gold standard light transmission aggregometry (LTA). A total of 11,913 patients who sequentially underwent LTA assessment using several stimuli (ADP-2µM, collagen-2 µg/ml, arachidonic acid 0.5 mM, epinephrine 10µM) with a standardized methodology between 2004 and 2022 were screened. After application of inclusion-exclusion criteria, 5,901 patients were included and divided into five groups: healthy-volunteers (HV; N = 534); controls (CTR; N = 1073); aspirin-treated patients (ASA; 75-150 mg/die; N = 3280); clopidogrel-treated patients (CLOP; 75 mg/die; N = 495) and patients treated with dual antiplatelet therapy, ASA plus CLOP (DAPT; N = 519). The mean PA% in response to ADP 2 μm was 72.4 ± 33.3 in the CTR population, 40.6 ± 29.9 in the ASA group, 25.1 ± 35.1 in the CLOP group and 10.2 ± 18.5 in the DAPT group. The mean PA% in response to collagen 2 ug/ml was 90.7 ± 10.5 in the CTR population, 40.8 ± 26.3 in the ASA group, 79.4 ± 21.8 in the CLOP group and 17.9 ± 19.9 in the DAPT group. The percentage of patients at OPR following ADP stimuli was 66%, 25%, and 26%, in the ASA, CLOP, and DAPT group, respectively. The percentage of patients at OPR following collagen stimuli was 56%, 22%, and 41%, in the ASA, CLOP, and DAPT group, respectively. LTA was significantly increased in response to ADP (72.4 ± 33.3vs62.7 ± 37.1; p < 0.001) and AA (90.7 ± 15.6vs87.6 ± 20.5; p < 0.001) in CTR compared to HV. Our findings support the concept that a significant proportion of individuals present a hyper- or hypo-reactive platelet phenotype potentially affecting the safety and efficacy of antiplatelet therapy. The variability in response to antiplatelet therapy was particularly evident in patients undergoing single as opposed to dual antiplatelet therapy regimens. These data support ongoing strategies of guided selection of antiplatelet therapy in patients with cardiovascular disease.

Complex Pattern of Platelet Activation/Reactivity After SARS-CoV-2 Infection

COVID-19 and post-COVID (long COVID) are associated with thromboembolic complications; however, it is still not clear whether platelets play a leading role in this phenomenon. The platelet hyperreactivity could result from the direct interaction between platelets and viral elements or the response to inflammatory and prothrombotic factors released from blood and vessel cells following infection. The existing literature does not provide clear-cut answers, as the results determining platelet status vary according to methodology. Elevated levels of soluble markers of platelet activation (P selectin, PF4), increased platelet aggregates, and platelet-derived microparticles suggest the activation of platelets circulating in the bloodstream of COVID-19 patients. Similarly, platelets isolated from COVID-19 patients demonstrate increased reactivity in response to collagen, thrombin, and ADP. By contrast, an analysis of whole blood from COVID-19 patients indicates the reduced activation of the fibrinogen receptor. Similarly, some in vitro studies report potential targets for SARS-CoV-2 in platelets, whereas others do not indicate any direct effect of the virus on platelets. The aim of this work is to review and evaluate the reliability of the methodology for testing platelet function after contact with SARS-CoV-2. Despite the diversity of methods yielding varying results and the influence of plasma components or blood cells, it can be concluded that platelets play an important role in the development of thrombotic complications after exposure to SARS-CoV-2.

Light transmission aggregometry for platelet function testing: position paper on current recommendations and French proposals for accreditation

Light transmission aggregometry (LTA) is a method used to investigate platelet functions in platelet-rich plasma (PRP), notably when screening for platelet disorders. Various national guidelines and recommendations help in setting up the LTA test in specialized laboratories. However, due to the nature of the sample matrix and its subsequent specificities, more accurate positions are needed to achieve LTA accreditation according to the standard NF EN ISO 15 189. We reviewed guidelines and recommendations as they can be useful in the accreditation process, and we conducted a survey on LTA practice among members of the Société Française de Thrombose et d'Hémostase (SFTH) in 2021. We formulated 28 proposals, which have been approved by vote within the SFTH. All aspects to take into consideration for the proper conduct of LTA assays and their accreditation have been covered. Notably, preanalytical, analytical and postanalytical aspects are depicted, including blood sampling, PRP preparation, instruments, agonists, performance assessment, personnel training and data interpretation. This document, essentially representing a French position paper on the current recommendations and subsequent proposals for LTA accreditation, might prove useful also outside France for relevant laboratories and auditors involved in LTA accreditation.

Bleeding Disorder of Unknown Cause: A Diagnosis of Exclusion

Patients with an unexplained mild to moderate bleeding tendency are diagnosed with bleeding disorder of unknown cause (BDUC), a classification reached after ruling out other mild to moderate bleeding disorders (MBD) including von Willebrand disease (VWD), platelet function defects (PFDs), coagulation factor deficiencies (CFDs), and non-hemostatic causes for bleeding. This review outlines our diagnostic approach to BDUC, a diagnosis of exclusion, drawing on current guidelines and insights from the Vienna Bleeding Biobank (VIBB). According to guidelines, we diagnose VWD based on VWF antigen and/or activity levels ≤50 IU/dL, with repeated VWF testing if VWF levels are <80 IU/dL. This has been introduced in our clinical routine after our findings of diagnostically relevant fluctuations of VWF levels in a high proportion of MBD patients. PFDs are identified through repeated abnormalities in light transmission aggregometry (LTA), flow cytometric mepacrine fluorescence, and glycoprotein expression analysis. Nevertheless, we experience diagnostic challenges with regard to reproducibility and unspecific alterations of LTA. For factor (F) VIII and FIX deficiency, a cutoff of 50% is utilized to ensure detection of mild hemophilia A or B. We apply established cutoffs for other rare CFD being aware that these do not clearly reflect the causal role of the bleeding tendency. Investigations into very rare bleeding disorders due to hyperfibrinolysis or increase in natural anticoagulants are limited to cases with a notable family history or distinct bleeding phenotypes considering cost-effectiveness. While the pathogenesis of BDUC remains unknown, further explorations of this intriguing area may reveal new mechanisms and therapeutic targets.

The study of platelet aggregation using a microtiter plate reader ‒ methodological considerations

Optical aggregometry by 96-well plate assay, the microplate method, is a fast, efficient, and readily available method for measuring the pharmacological effects of antiplatelet drugs. Even though recent years have witnessed growing interest in adopting the microplate method for widespread use, it remains in the shadow of the standard light transmission aggregometry (LTA). Regardless of the method used, the results of platelet aggregation depend on a variety of factors and often vary among laboratories worldwide. While several methodological papers have examined the microplate method, no standards have been established, most likely because the approach is not used as a diagnostic tool. Currently, the microplate method is recommended by researchers to be used in conjunction with LTA or as an adjunct to LTA. This raises the question of whether an optimal protocol exists for microplate aggregometry, and what are the key considerations in a good experimental protocol for obtaining reliable results? This article attempts to address these questions by summarizing the knowledge accumulated in this field over the last three decades.