Abstract
Introduction
Myeloproliferative neoplasm (MPN), such as polycythaemia vera (PV) and essential thrombocythaemia (ET), are independent risk factors for arterial and venous thrombotic events, with the estimated risks of thrombotic complications at diagnosis to be approximately 7-26% in ET patients and 19-32% in PV patients. As such, one of the management goals for MPN is directed towards modifying thrombosis risk via cytoreduction and anti-platelet therapies. However, there are no routinely available laboratory tests to evaluate the patient's thrombotic risk beyond the assessment of blood counts. Global coagulation assays such as thromboelastography, thrombin and fibrin generation may be better surrogate measures of thrombosis. This pilot study evaluates a cohort of MPN patients on current treatment, to further elucidate the impact of their prothrombotic milieu on global coagulation assays.
Methods
Participants with MPN (proven on bone marrow biopsy and/or molecular diagnosis) were recruited. Thromboelastography (using TEG® 5000) was performed on citrated whole blood while additional citrated blood samples were double spun at -2500G to obtain platelet-poor plasma (PPP) and stored in at -80°C within 2 hours of sample collection. The stored PPP were then used for thrombin generation assessment using the calibrated automated thrombogram (CAT), fibrinolysis evaluation using overall haemostatic potential assay (OHP) as well as p-selectin testing. The results were compared to our previously collected age-matched healthy normal controls (n=41).
Results
Thirty-eight MPN patients (20 females, 18 males) with median age 65 years (range: 29-84) were recruited. There were 26 patients with ET (68.4%) including a patient with post-ET myelofibrosis, 8 patients with PV (20.5%), 3 patients with primary myelofibrosis and one with MPN, unclassifiable. The majority of the patients are JAK2 V617F positive (30/38, 79%). The haemoglobin level was comparable between both groups (p=0.73) although the MPN group had significantly increased platelet count (526 vs 237 x 109/L, p<0.01).
When compared to normal controls, the thromboelastography parameters were mostly comparable including no significant difference in maximum amplitude or clot strength (59.6 vs 60.1 mm, p=0.42) although the clot lysis time (LY30) was significantly higher (5.1% vs 0.9%, p<0.01) in the MPN group, independent of the use of aspirin. Higher LY30 (>5%) was associated with higher haemoglobin (150.3 vs 138.4 g/L, p=0.03) but not platelet count. CAT parameters, however, showed higher thrombin peak (260.8 vs 227.3 nM; p=0.01) and velocity index (93.4 vs 70.1 nM.min; p<0.01) compared to the normal controls, but interestingly no difference in endogenous thrombin potential (1397.5 vs 1363.0 nM.min, p=0.52).
Fibrin generation parameters, namely the overall coagulation potential (OCP) and OHP were significantly reduced in the MPN cohort (OCP - 56.5 vs 66.7, p<0.001; OHP - 27.4 vs 33.0, p<0.001) with preserved overall fibrinolytic potential (p=0.66). P-selectin was markedly increased in MPN patients compared to the normal controls (116.3 vs 54.6 ng/mL, p<0.001), with higher P-selectin levels correlating with a higher platelet counts (p<0.01).
Conclusion
This study demonstrates that global coagulation assays can provide additional information regarding the thrombotic risks in MPN patients. The MPN patients in our study had significantly higher lysis time and a reduction in fibrin generation parameters, which is contradictory to the prothrombotic nature of MPN. It may be a protective prognostic marker in the setting of treatment and could represent an underlying compensatory effect. Despite being a treated MPN cohort, the P-selectin remained higher in these patients and correlated with higher platelet count, suggesting that the higher P-selectin seen is likely of platelet subtype, though this did not correlate with changes in other global coagulation assay parameters despite thrombin being a known trigger of P-selectin exocytosis. Further prospective clinical studies including assessment of fibrinolysis markers and markers of platelet and endothelial function to evaluate and confirm these findings are proposed.
No relevant conflicts of interest to declare.
