PB1315 - Procoagulant platelets in essential thrombocytosis: Relationship with JAK2V617F allele burden and validation of a novel associated GSAO+ platelet subpopulation

Background: Procoagulant platelets can be detected through the uptake of a tripeptide trivalent arsenical (GSAO) combined with P-selectin expression. These procoagulant platelets are elevated in essential thrombocytosis (ET), especially in JAK2V617F mutated ET. Recently, a novel GSAO+ platelet subpopulation arisen from procoagulant platelet assay has been demonstrated to be a potential biomarker in ET, where ET patients with high GSAO+ subpopulation are at increased thrombotic risk.

Aims: To evaluate the correlation between procoagulant platelet response and JAK2V617F allele burden and to validate the clinical utility of high GSAO+ subpopulation in ET.

Methods: Patients with ET are prospectively recruited for procoagulant platelet and are followed up for new thrombotic complications. The assay used is a whole blood flow cytometry-based method using markers CD41, CD45, GSAO and P-selectin. Paired JAK2V617F allele burden is performed. Samples are stimulated with thrombin 5U/mL and collagen 10µg/mL. A further subset of GSAO+ subpopulation is identified through multiparameter clustering and gating approach. Using previously defined cut-off of >2.09%, patients are dichotomised into high GSAO+ group and non-high GSAO+ group.

Results: Seven patients with ET were recruited with their characteristics shown in Table 1. ET patients have increased procoagulant platelets compared to healthy controls (P < 0.05) (Figure 1a). There was no correlation between procoagulant platelet response and paired JAK2V617F allele burden (P>0.05). None of the patients expressed GSAO+ platelet subpopulation >2.09% and are therefore classified as non-high GSAO+ group. After a median follow up of 23 months, no new thrombotic event is reported.

Conclusion(s): Procoagulant platelet response in ET is increased but JAK2V617F allele burden does not seem to influence this heightened response. The absence of new thrombotic event so far is not unexpected as all the patients are of non-high GSAO+ group. More data are needed to conclusively validate the clinical utility of this GSAO+ platelet subpopulation.