Condition Overview

What is polycythemia vera?

Polycythemia vera (PV) is a rare blood cancer caused by a mutation in the bone marrow's blood-forming cells. The bone marrow produces too many red blood cells, and often too many white blood cells and platelets as well. This excess thickens the blood, slowing circulation and raising the risk of blood clots.

What causes it?

More than 95% of PV cases are caused by a mutation in the JAK2 gene — specifically the JAK2 V617F variant. This mutation makes the JAK2 protein permanently active, driving uncontrolled blood cell production. The mutation is acquired (not inherited) and develops in a single stem cell over time.

How is it treated?

The cornerstone of PV treatment is therapeutic phlebotomy — removing 450–500 mL of blood regularly to reduce hematocrit below 45%. Low-dose aspirin (81 mg/day) is recommended for most patients to reduce clot risk. Higher-risk patients may also take cytoreductive therapy (hydroxyurea or ruxolitinib) to suppress blood cell production. Regular monitoring of CBC and symptom burden is essential.

Key risks to monitor

The two main long-term risks of PV are thrombosis (blood clots in veins or arteries, including stroke and heart attack) and disease progression — either to post-PV myelofibrosis (scarring of the bone marrow) or, rarely, to acute leukemia. Maintaining tight HCT control below 45% significantly reduces thrombotic risk. Fatigue, itching (aquagenic pruritus), night sweats, and splenomegaly are common symptoms.

Your key lab targets

Hematocrit: <45% (primary goal). WBC: <10 ×10³/µL for lower-risk patients. Platelet count: ideally <400 ×10³/µL. HRV and recovery trends via Whoop help detect early signs of hyperviscosity or disease activity between blood draws.