[poly- + cyto- + -emia]
An excess of red blood cells. In a newborn, for example, it may reflect hemoconcentration due to hypovolemia or prolonged intrauterine hypoxia, or hypervolemia due to intrauterine twin-to-twin transfusion or placental transfusion resulting in delayed clamping of the umbilical cord.
SYN: SEE: erythrocytosis
An autosomal recessive erythrocytosis in which patients respond to normal oxygen levels as if they were in an hypoxic environment and make more red blood cells than are needed. Sludging of blood, pulmonary hypertension, and vascular infarcts are common sequelae.
A relative rather than an absolute increase in the number of erythrocytes due to a reduction of plasma volume, e.g., in patients with burns or dehydration.
Polycythemia due to a physiological condition that stimulates erythropoiesis, e.g., lowered oxygen tension in blood.
SEE: Gaisböck syndrome.
A chronic, life-shortening myeloproliferative disorder due to the reproduction of a single stem-cell clone. It is characterized by proliferation or hyperplasia of all bone marrow cells, with an increase in red blood cell mass and hemoglobin concentration that occurs independently of erythropoietin stimulation.
SYN: SEE: erythremia
POLYCYTHEMIA VERA Peripheral blood smear in polycythemia vera (×400)
Usually occurring between ages 40 and 60 and most common in males with Jewish ancestry, polycythemia seldom affects children or those of African ancestry. Weakness, fatigue, headache, blood clotting, vertigo, tinnitus, irritability, dyspnea, visual disturbances, flushing of face, redness or ruddy cyanosis, pruritus, ecchymosis, hypertension, epigastric distress, weight loss, and pain in joints or extremities occur commonly. The bone marrow shows uncontrolled, rapid cellular reproduction and maturation (increased cellularity). Peptic ulcers are often reported.
The disease should be suspected in people with high hemoglobin concentrations who have no other explanation for this finding (such as low oxygen concentration or exogenous testosterone use). It is confirmed by the presence of an elevated red cell mass, low erythropoietin, and a JAK2 mutation.
The mainstay of patient care is the reduction in red blood cell mass with recurrent phlebotomy to lower the hematocrit to 45% or less. Patients whose risk for blood clotting is high should also take myelosuppressive drug therapy (such as hydroxyurea). Low dose aspirin may be given as adjunct therapy. Protective measures are instituted.
Vital signs are monitored during and after phlebotomy, and the patient is provided with oral fluids and protected from orthostatic hypotension. The symptoms and the need to seek medical attention when signs and symptoms of bleeding and thrombus formation occur are explained to the patient. Rest should be balanced with exercise, but the patient should be advised that activity and ambulation help prevent thrombotic complications. Reassurance and support are provided to the patient and family, and opportunities are provided for questions and discussion of concerns. Patients who have a history of blood clotting or very high platelet counts are treated with myelosuppressive drugs, such as hydroxyurea. During myelosuppressive therapy the patient is informed about adverse effects that may occur and is assessed for leukopenia and thrombocytopenia. Protective measures are instituted.
POLYCYTHEMIA VERA Bone marrow showing hypercellularity and increased megakaryocytes (arrows)
Taber’s Cyclopedic Medical Dictionary Online + App from F.A. Davis and Unbound Medicine. Find 75,000 medical and nursing definitions. Download to iPhone, iPad, and Android. Complete Product Information.