Polycythemia vera (PV), a hematological neoplasm characterized by excessive erythropoiesis due to Janus kinase 2 (JAK2)- activating mutations. On the other hand, patients with secondary polycythemia (SP), a disorder mostly caused by an increased red cell mass due to chronic hypoxia (i.e, pulmonary disorders and smoking) and erythropoietin-producing tumors (such as leiomyoma, hemangiomas, renal cysts and various carcinomas), are phenotypically slightly different and are usually considered to have significantly better outcomes.

Red blood cell distribution width (RDW) reflects the heterogeneity of red blood cell sizes (anisocytosis) and is routinely reported as a part of complete blood count by automated instruments in hematology laboratories.

We will collect data about clinical manifestations at the time of diagnosis, history of thrombosis and investigations as complete blood picture, including Hematocrit and haemoglobin level, serum uric acid, JAK2V617F mutation status by real time PCR (Polymerase Chain Reaction), bone marrow aspiration and biopsy with reticulin stain.

Patients with secondary erythrocytosis will be included as controls and will be recruited from Sohag university hospital especially internal medicine department and chest department.

Inclusion Criteria:

• All patients aged 18 years and older who were newly diagnosed to have polycythemia vera between September 2014 and November 2022 at Sohag university hospital, department of internal medicine, hematology unit and hematology outpatient clinic.

Exclusion Criteria:

• Patients were excluded if: (1) their disease was not newly diagnosed, (2) their disease met WHO criteria for chronic, acute myeloid leukemia or other myeloid neoplasms.

patients with polycythemia vera who were diagnosed according to the WHO 2016 criteria, at Sohag university hospital, department of internal medicine, hematology unit and hematology outpatient clinic