Diagnosis and treatment of true erythrocytosis (Polycythemia vera, PV) is one of the classical Ph-myeloproliferative neoplasms and is due to an overreaction to EPO and overproliferation of hematopoietic progenitor cells of the red lineage due to an intrinsic somatic mutation. Clinical manifestations are due to increased blood volume as well as increased blood viscosity causing slow blood flow. Common symptoms include dizziness, headache, fatigue, shortness of breath, fear of heat, sweating, epigastric fullness, numbness in the limbs, and often facial and palmar flushing. There are also patients who do not have any symptoms and are found during physical examination. The JAK2V617F mutation is a major development in the pathogenesis of PV. 95% of patients with PV have this mutation, and about 4% have the JAK2 exon12 mutation. JAK2 mutation inhibitors have been clinically tested overseas and have failed to effectively reduce JAK2V617F gene load, although patients have improved general status and reduced spleen size. Approximately 10% of patients with PV have disease progression to myelofibrosis, and very few patients have disease progression to leukemia. Current PV treatment focuses on lowering red blood cells, improving symptoms, preventing disease progression as much as possible, and preventing thrombosis. Erythrocyte-lowering therapy includes bloodletting, hydroxyurea and interferon. The remission rate of PV can reach 80% with interferon therapy, which can shrink the spleen, and interferon therapy can significantly reduce the JAK2V617F gene load in some patients, which may lead to molecular remission in 5-10% of patients. aspirin should be chosen to prevent thrombosis in all PV patients without clinical contraindications. Department of Hematology, Xuanwu Hospital, Capital Medical University, Huizhou Wuhuan Diagnostic criteria for true erythrocytosis 2008 WHO diagnostic criteria Primary criteria Hemoglobin >18.5 g/dL (men),>16.5 g/dL (women), or evidence of increased red blood cell volume Presence of JAK2V617F or other functional gene mutation (e.g., JAK2 exon 12) Secondary criteria Bone marrow biopsy Demonstrate triple lineage hyperplasia (all myelodysplasia) compared to age corresponding to age with significant hyperplasia of the red, granulocytic and megakaryocytic lineages Serum EPO levels below normal in vitro endogenous red lineage colony growth Diagnosis requires meeting 2 primary criteria and one secondary criterion or the first of the primary criteria with two secondary criteria Differential diagnosis Secondary erythropoiesis that can be caused by hypoxia-related cardiopulmonary disease, smoking, CO toxicity, sleep apnea syndrome, brain tumors, hepatocellular carcinoma, adrenal tumors, and plasma cell disease should be distinguished. Thrombotic risk assessment Low risk group Age <60 years, no history of thrombosis High risk group Age >60 years or history of thrombosis Disease progression assessment is difficult to predict whether patients with PV will progress to myelofibrosis, but some studies have shown that leukocytes >15×109/L and JAK2V617F gene load >50% are high risk factors for disease progression to myelofibrosis.PV progression to leukemia is rare and may be related to the patient’s advanced age as well as a high white blood cell count. Treatment controls cardiovascular risk factors, such as hypertension, diabetes, hyperlipidemia, smoking, and obesity. If not contraindicated, all PV patients are given aspirin 100 mg/day. Patients at low risk of thrombosis are treated with bloodletting, intermittently until the erythrocyte pressure is reduced to 45%. Patients at high risk of thrombosis, or with significant platelet elevation or leukocyte elevation, or with splenomegaly, or with clinically significant symptoms, are given hydroxyurea cytoreductive therapy. The starting dose of hydroxyurea is 1-1.5 g/day and is reduced to the lowest maintenance dose after the desired efficacy is achieved. Side effects of hydroxyurea include darkening of the skin and nails and skin ulcers on the lower legs. Interferon 3 million units 3 times/week is given to younger patients or those who are intolerant to hydroxyurea. Interferon is not indicated for patients with thyroid disease or psychiatric disorders.