1. Phlebotomy requirement to maintain hematocrit <45% after receiving ‡2 g/d hydroxyurea for ‡3 months

OR

2. Uncontrolled myeloproliferation after receiving ‡2 g/d hydroxyurea for ‡3 months (platelet count >400 × 109/l AND white blood cell count >10 × 109/l)

OR

3. Massive† splenomegaly reduced by £50% as measured by palpation, OR persistent splenomegaly-related symptoms, after receiving ‡2 g/d hydroxyurea for ‡3 months

OR

4. Absolute neutrophil count <1.0 × 109/l, OR platelet count <100 × 109/l, OR hemoglobin <100 g/l, with the lowest dose of hydroxyurea required to achieve complete or partial clinicohematologic response‡

OR

5. Presence of hydroxyurea-related nonhematologic toxicities, including leg ulcers, mucocutaneous manifestations, gastro-intestinal symptoms, pneumonitis, or fever

^†Spleen extending ‡10 cm from the costal margin.

^‡Per ELN 2009 criteria [41].

Adapted with permission from [51].