Hemoglobin >16.5 g/dL: defined as polycythemia in males
Hemoglobin >16.0 g/dL: defined as polycythemia in females
Hematocrit
Hematocrit >49%: defined as polycythemia in males
Hematocrit >48%: defined as polycythemia in females
Red Blood Cell Count: not used as often as hemoglobin and hematocrit in the diagnosis of polycythemia (since diseases such as thalassemia minor may have an elevated red blood cell count with a decreased hemoglobin or hematocrit due to an increased number of small/microcytic, poorly hemoglobinized/hypochromic red blood cells)
Epidemiology: occurs in 36% of cases (Leukemia, 2013) [MEDLINE]
Possible Physiologic Mechanisms
Mast Cell Degranulation: with release of histamine, fibrinolytic factors, prostaglandins, and/or IL-31)
Release of Adenosine Disphosphate from Red Blood Cells or Release of Catecholamines from Adrenergic Vasoconstrictor Nerves When the Skin is Cooled: resulting in platelet aggregation in the skin blood vessels with local production of prostaglandins (which cause pruritus)
Clinical
Aquagenic Pruritus (Pruritus Following a Warm Bath/Shower): common (and may be present for years prior to the formal diagnosis of polycythemia vera)
Excoriation of the Skin May Be Seen in Association with the Pruritus
Epidemiology: occurs in 50% of cases (Leukemia, 2013) [MEDLINE]
Endogenous Erythroid Colony Formation
Epidemiology: occurs in 73% of cases (Leukemia, 2013) [MEDLINE]
Diagnosis: performed using in vitro culture technique (available only in specialized centers) -> formation of erythroid colonies in the absence of exogenous erythropoietin
Hemorrhage
Epidemiology: major hemorrhage occurs in 4% of cases (Leukemia, 2013) [MEDLINE]
Survival and prognosis among 1545 patients with contemporary polycythemia vera: an international study. Leukemia. 2013;27(9):1874. Epub 2013 Jun 6 [MEDLINE]