Blood Viscosity in Polycythemia Patients

Whole blood viscosity levels in patients with polycythemia

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.