Utility of the Platelet Function Analyzer in Patients with Suspected Platelet Function Disorders: Diagnostic Accuracy Study

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.

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.

Primary hemostasis in fetal growth restricted neonates studied via PFA-100 in cord blood samples

BACKGROUND

Platelet function of fetal growth restricted (FGR) neonates remains a field of debate. Platelet function analyzer (PFA-100) offers a quantitative in vitro assessment of primary, platelet-related hemostasis. Our aim was to examine platelet function using PFA-100 in FGR neonates and associate our results with perinatal parameters.

METHODS

PFA-100 was applied on 74 FGR neonates, 48 full-term (>37 weeks' gestation) and 26 preterm neonates (<37 weeks). The control group consisted of 118 healthy neonates. Two closure times (CTs) with COL/EPI and COL/ADP cartridges were determined on cord blood samples for each subject. Statistical analysis was performed by SAS 9.4. The statistical significance level was set at 0.05 and all tests were two-tailed.

RESULTS

COL/EPI CTs were prolonged in FGR (median 132 s, IQR 95-181 s) compared with control neonates (median 112.5 s, IQR 93-145 s), p = 0.04. Median COL/EPI CT for term and preterm FGR neonates was 126 s (IQR 90-157 s) and 137 s (IQR 104-203), respectively (p = 0.001), and COL/ADP CT was 70 s (IQR 62-80 s) for term and 75 s (IQR 68-82 s) for preterm FGR neonates (p = 0.08). Among FGR neonates, COL/EPI CT was related with delivery time (with preterm neonates exhibiting prolonged COL/EPI CTs), p = 0.05. No correlation was proved between both CTs and hematological parameters in FGR neonates.

CONCLUSION

FGR neonates showed impaired platelet function via PFA-100, with preterm FGR neonates confronting the greatest risk. Prolonged COL/EPI CTs in FGR neonates seemed to be independent of hematological parameters and could warn for closer evaluation during the first days of their lives.

Platelet Phenotyping and Function Testing in Thrombocytopenia

Patients who suffer from inherited or acquired thrombocytopenia can be also affected by platelet function defects, which potentially increase the risk of severe and life-threatening bleeding complications. A plethora of tests and assays for platelet phenotyping and function analysis are available, which are, in part, feasible in clinical practice due to adequate point-of-care qualities. However, most of them are time-consuming, require experienced and skilled personnel for platelet handling and processing, and are therefore well-established only in specialized laboratories. This review summarizes major indications, methods/assays for platelet phenotyping, and in vitro function testing in blood samples with reduced platelet count in relation to their clinical practicability. In addition, the diagnostic significance, difficulties, and challenges of selected tests to evaluate the hemostatic capacity and specific defects of platelets with reduced number are addressed.