Background: Immune thrombocytopenia (ITP) is associated with a heterogeneous clinical presentation, which cannot be predicted by the platelet count. Platelet activation might influence the clinical presentation of ITP.

Aims: To investigate platelet activation in a cohort of 51 adult patients with primary ITP and 18 age- and sex-matched non-immunological thrombocytopenic controls (TPC).

Methods: Patients were included in two haematological centers after written informed consent (EC1843/2016). Soluble P-selectin (sPsel) levels and platelet function by flow cytometry, uninitiated and after addition of agonists were assessed.

Results: Patient characteristics are shown in Table 1. All analyses were adjusted for platelet counts. Median sPsel levels [25-75 percentile] and non-activated CD62P were increased in ITP compared to TPC (sPsel 31.7 [23.3-52.2] and 14.5 [5.1-23.9], p=0.002; CD62P 0.0 [0.0-9.5] and 0.0 [0.0-0.0], p=0.044; Figure 1). ITP patients under treatment had higher sPsel-levels than untreated patients (44.3 [30.7-61.2] and 28.2 [19.6-47.5], p=0.013), whereas there was no difference in other parameters of platelet function. TPO-RA-treated patients had higher median sPsel and lower PAC-1 ADP than untreated patients (sPsel 60.5 [33.8-70.0] and 27.3 [17.3-47.2], p=0.019; PAC-1 ADP 40.8 [18.1-75.7] and 157.6 [63.9-267.5], p=0.017), while there was no difference in comparison to corticosteroid-treated patients (sPsel 38.6 [24.8- 60.9], p=0.181 and PAC1-ADP 90.7 [23.1-366.1], p=0.784). Splenectomized patients tended towards higher sPsel-levels compared to non-splenectomized (46.4 [30.4-70.6] and 30.6 [17.6- 50.4], p=0.056). Previous thrombosis had no impact on sPsel-levels or platelet activation markers. Bleeding severity, assessed by the ISTH-ITP-BAT showed a weak correlation with unactivated CD62P (ß=0.34, p=0.016), whereas there was no correlation with sPsel or other parameters of platelet activity.

Patients´ clinical and laboratory characteristics
Comparison of sP-selectin (ng/ml) and unactivated CD62P MFI (median fluorescence intensity) between ITP patients and non-immunological thrombocytopenic controls (TPC)

Conclusions: ITP-patients have increased sPsel, especially under TPO-RA-treatment, whereas there was no clear pattern of platelet hyperreactivity. There was no association or correlation of platelet activation markers with previous thrombosis or bleeding severity.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/platelet-activation-and-function-in-adult-patients-with-primary-immune-thrombocytopenia/