Platelet function analyzer (PFA-100) in patients with bleeding disorder of unknown cause

Introduction Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion. BDUC patients exhibit a clinical phenotype similar to that of established mild-to-moderate bleeding disorders (MBDs) such as platelet function defects (PFD), von Willebrand Disease (VWD), or coagulation factor deficiencies (CFD). While the PFA-100 has demonstrated sensitivity in the detection of VWD, data regarding its clinical utility in PFD are conflicting and data on PFA-100 in BDUC patients are scarce. The aim of this study was to evaluate the diagnostic utility of PFA-100 in BDUC compared to other MBDs, and to investigate the influence of various parameters on PFA-100 closure time (CT).

Method We analyzed PFA-100 measurements of 821 MBD patients from in the Vienna Bleeding Biobank, who were included until December 2022. Patients receiving anticoagulation or antiplatelet treatments were excluded from the study. PFA-100®​ (Dade Behring, Newark, Delaware, USA) analyses with collagen-epinephrine (EPI) and collagen-adenosine diphosphate (ADP) cartridges were conducted on citric acid anticoagulated whole blood samples at study inclusion.

Results In total, 535 BDUC patients (65.1%) were compared to 79 patients (9.6%) with VWD, 180 (21.9%) with PFD, and 27 (3.3%) with CFD ([Fig. 1]).

Fig. 1  Clinical characteristics and PFA-100 in MBD patients

In BDUC patients, median (interquartile range [IQR]) CTs were 102 sec (88-117) in PFA-EPI and 135 sec (112-163) in PFA-ADP ([Fig. 1]). Both CTs in BDUC patients were shorter than those of VWD (p<.001) and PFD patients (p<.001), though no significant difference was observed in comparison to CFD (PFA-EPI: p=0.2; PFA-ADP: p=0.7).

Applying internal reference standards (PFA-EPI: 82-170 sec; PFA-ADP: 74-130 sec), 341 BDUC patients (64%) exhibited an abnormal CT in PFA-ADP or PFA-EPI, and 11 patients (2%) displayed abnormalities in both, similar to CFD patients ([Fig. 1]). The rate of pathological CTs was much higher in VWD (no abnormal CT: 9%, 1 abnormal CT: 58%, 2 abnormal CTs: 33%; p<.001), as well PFD (no abnormal CT: 24%, 1 abnormal CT: 69%, 2 abnormal CTs:7%; p=0.003) compared to BDUC.

In BDUC patients there was no correlation between PFA-EPI and PFA-ADP CTs and the Vicenza bleeding score (PFA-EPI: Spearman rho (r)=0.03, p=0.5; PFA-ADP: r=0.04, p=0.4), ISTH-BAT (PFA-EPI: r=0.06, p=0.3; PFA-ADP: r=0.10, p=0.06), or the number of bleeding manifestations (PFA-EPI: r=0.01, p=0.8; PFA-ADP: r=-0.01, p=0.8).

Employing a Tobit regression model, we identified increasing age, reduced hematocrit, lower VWF:Ag/VWF:RCo levels, lower platelet count, and elevated fibrinogen levels to be associated with extended CTs in PFA-EPI and PFA-ADP ([Fig. 2]).

Fig. 2  Univariable and multivariable Tobit regression models for the association of clinical and laboratory parameters with PFA-Epinephrine and PFA-ADP in all BDUC patients

Conclusion Two thirds of BDUC patients had prolongations in any PFA-100 CT. Nevertheless, pathologic PFA-100 measurements were less common than in patients with known defects of primary hemostasis. Factors known to influence PFA-100 CTs were also identified as relevant in BDUC patients.

Conflict of Interest

The authors have no conflict of interest with regards to this study. D.M. received honoraria for advisory board meetings from CSL Behring. C.A. received honoraria from Bayer, CSL Behring, Novo Nordisk, Pfizer, Roche, Sobi, and Takeda for lectures and/or participation in advisory board meetings. I.P. has occasionally received honoraria from Bayer, CSL Behring, Novo-Nordisk, Pfizer, Roche, Sobi, and Takeda for lectures and advisory board meetings. J.G. received honoraria for lectures, advisory board meetings, and research funding for the Medical University of Vienna from CSL Behring, Novartis, Amgen, and Sobi. A.T., J.B., P.Q., and H.H. have no conflicts of interest to declare.

Publication History

Article published online:
26 February 2024