The haematocrit and platelet target in polycythemia vera

Polycythemia vera (PV) is a chronic myeloproliferative disorder whose majormorbidity and mortality are thrombohaemorragic events and progression to acuteleukaemia or myelofibrosis. Whether the haematocrit and platelet count predictsuch complications remains unclear. The European Collaboration on Low-doseAspirin in Polycythemia Vera prospective study included 1638 PV patients. A totalof 164 deaths (10%), 145 (8.85%) major thrombosis and 226 (13.8%) totalthrombosis were encountered during 4393 person-years follow-up (median 2.8years). In time-dependent multivariable analysis, a haematocrit in the evaluable range of 40-55% was neither associated with the occurrence of thrombotic events, mortality nor with haematological progression in the studied population. Thehaematocrit of patients in the highest and lowest deciles at baseline wasmaintained within a narrow interval of haematocrit values ranging from 40% to 47%throughout follow-up. High platelet count was associated with a lower progressionrate to acute leukaemia/myelofibrosis, whereas it had no significant relationshipwith thrombotic events or mortality. Our findings do not suggest that the rangeof haematocrit (<55%) and platelet counts (<600 x 10(9)/l) we encountered in our population had an impact on the outcome of PV patients treated by currenttherapeutic strategies.