The following information is from the respected medical database, "Up To Date:
Diagnostic approach to the patient with polycythemia
Ayalew Tefferi, MD
Stanley L Schrier, MD
Stephen A Landaw, MD, PhD
Last literature review version 17.1: February 2009 | This topic last updated: February 2, 2007 (More)
INTRODUCTION — The diagnosis of polycythemia is most commonly suspected in a patient with an abnormally high result on one or more of the following blood tests :
Hematocrit — The hematocrit (HCT) is expressed as the percent of a blood sample occupied by intact RBCs. Polycythemia is suspected when the HCT is >48 or >52 percent in women and men, respectively.
Hemoglobin concentration — The hemoglobin concentration (HGB) is its content in grams per 100 mL of whole blood. Polycythemia is suspected when the HGB is >16.5 or >18.5 g/dL in women and men, respectively.
Red blood cell count — The red blood cell (RBC) count is expressed as the number of RBC per microL or L of whole blood. It is least often used to suggest polycythemia since patients with thalassemia minor may have an elevated RBC count, but a normal or reduced HCT or HGB due presence of small (microcytic), poorly hemoglobinized (hypochromic) red cells.
The approach to the patient with an elevation in one or more of the above RBC parameters will be reviewed here. The approach to confirming a diagnosis of polycythemia vera is discussed separately. (See "Diagnostic approach to the patient with suspected polycythemia vera").
TERMINOLOGY — The three measurements listed above (RBC count, HGB, and HCT) are concentrations and therefore dependent upon the plasma volume as well as the RBC mass (RCM).
Relative polycythemia — An isolated decrease in plasma volume can elevate the hemoglobin, hematocrit, and RBC count. The state of chronically reduced plasma volume with elevated hemoglobin or hematocrit has been called Gaisbock's disease, spurious polycythemia, stress erythrocytosis, apparent polycythemia, and pseudopolycythemia [2-5], although many may be examples of smokers' polycythemia (see "Reduced plasma volume" below) .
Absolute polycythemia — In absolute polycythemia (erythrocytosis) there is an increased RCM. Patients are further categorized into primary and secondary forms (show table 1):
Primary polycythemia — Primary polycythemia is caused by an acquired or inherited mutation leading to an abnormality within RBC progenitors; it includes polycythemia vera and rare familial variants (eg, activating mutations of the erythropoietin receptor, Chuvash polycythemia). (See "Molecular pathogenesis of congenital polycythemic disorders and polycythemia vera").
Idiopathic erythrocytosis has been used to categorize patients with primary polycythemia who do not fulfill conventional criteria for the diagnosis of polycythemia vera , including negativity for the exon 14 V617F mutation of JAK2 . The status of this term may change in the near future, since some patients considered to have idiopathic erythrocytosis have been found to have JAK2 mutations within exon 12 rather than exon 14 [9,10]. (See "Overview of the myeloproliferative neoplasms", section on JAK2 mutation).
Secondary polycythemia — Secondary polycythemia is caused by a circulating factor stimulating erythropoiesis, usually erythropoietin (Epo). It is most often due to an Epo response to hypoxia, but can also result from an Epo-secreting tumor. (See "Molecular pathogenesis of congenital polycythemic disorders and polycythemia vera" and see "Tumor polycythemia" below).
Combined polycythemia — Patients may have an increased RCM as well as a reduced plasma volume, a combination most commonly seen in smokers (ie, "smokers' polycythemia") .
Inapparent polycythemia — If the RCM and plasma volume are equally increased, HGB and HCT remain normal . Polycythemia can only be detected via blood volume studies.
PHYSIOLOGY OF ERYTHROPOIESIS — Similar to all other blood cells, red blood cells (RBCs) are derived from the pluripotent hematopoietic stem cell after a hierarchical process of lineage-commitment and differentiation. Under normal conditions, the earliest, erythroid- committed progenitor cells depend on the trophic hormone erythropoietin (Epo) to further differentiate and produce RBC. (See "Overview of hematopoiesis and stem cell function").
Ninety percent of the circulating Epo in humans is synthesized by the kidneys in response to a hypoxic signal. The hypoxic signal to the Epo-producing renal cells may be the result of reductions in hemoglobin concentration (anemia, show figure 1), reduced oxygen saturation (hypoxemia), decreased oxygen release from hemoglobin (eg, high oxygen-affinity hemoglobinopathies), or reduced oxygen delivery to the kidney (eg, vascular occlusion). (See "Regulation of erythropoiesis", section on Hypoxia-inducible factor-1 and the response to hypoxia).
"Up to Date", and I am a pharmacist