Secondary polycythemia (also called “secondary erythrocytosis”) is not a myeloproliferative neoplasm. It may occur as a result of:
- Ascent to high altitude
- Diseases that lead to low oxygenation of the blood
- Tumours that secrete the hormone erythropoietin (e.g., kidney tumours)
- Inherited disorders that result in overproduction or exaggerated action of erythropoietin.
Secondary polycythemia is limited to overproduction of red cells. In the case of high altitude or heart and lung diseases that lead to low blood oxygen content, secondary polycythemia is a physical response that the body makes to improve the oxygen-carrying capacity of the blood.
Patients with PV may have high platelet counts, which can contribute to the formation of clots (thrombi). Underlying vascular disease, common in older persons with PV, can increase the risk of clotting complications. The clots may cause serious problems, such as stroke, heart attack, deep vein thrombosis or pulmonary embolism.
Blood clots occur in about 30 percent of patients even before the PV diagnosis is made. During the first 10 years after a diagnosis of PV, 40 to 60 percent of untreated PV patients may develop blood clots.
PV patients who haven't undergone treatment have an increased risk of bleeding complications from surgery. If you need surgery for any reason, your doctor should first treat you to bring your hematocrit and hemoglobin levels to normal.
People with PV are at slightly greater risk than the general population for developing leukemia as a result of the disease and/or certain drug treatments.