Blood Viscosity in Polycythemia Patients

Polycythemia (PG) corresponds to an increase in erythrocyte parameters on a blood test. A distinction is usually made between primary and secondary PG. The most common primary PG is Vaquez's disease, a hematological cancer. In Vaquez disease, an increase in hematocrit has been reported to be associated with a logarithmic increase in blood viscosity. The main complications of primary PGs (especially in Vaquez disease) are thromboembolic complications. In contrast, thromboembolic complications are rarer in secondary PG. In Vaquez disease, a hematocrit ≤ 45% has been defined as the therapeutic goal for significantly reducing thromboembolic risk. However, this has not been established for secondary PGs. All in all, the definition of the 45% threshold is based solely on clinical studies with no obvious biological argument. What's more, simply lowering blood mass through cytoreduction alone does not appear to be sufficient to significantly reduce thromboembolic risk. To investigator knowledge, there are no studies prospectively evaluating blood viscosity, its determinants and coagulation in different types of polycythemia. Nor are there any data on the direct effect on blood viscosity of the various treatments usually offered.