TOC | HEME
Polycythemia or Erythrocytosis Relative Polycythemia | Polycythemia Vera
Polycythemia ("many cells") describes an increase in the total quantity or volume (mass) of red blood cells in the body, without any implication regarding leukocytes or platelets.
Erythrocytosis refers to an increase in the concentration of erythrocytes, however, whether measured as number of cells, hemoglobin, or packed cell volume (hematocrit). Erythrocytosis may be the result of
Polycythemia (rubra) vera is a myeloproliferative disorder associated with trilineage marrow hyperplasia and characterized by an increased red cell mass, usually in association with leukocytosis and thrombocytosis.
Classification of Erythrocytosis
1. Relative erythrocytosis or polycythemia (pseudoerythrocytosis)
2. Polycythemia (absolute erythrocytosis)
3. Polycythemia vera
4. Secondary polycythemia
5. Secondary to decreased tissue oxygenation (physiologically appropriate polycythemia or hypoxic erythrocytosis)
6. Secondary to aberrant erythropoietin production or response
7. Familial polycythemia
8. Idiopathic polycythemia
Phlebotomy can bring about a significant clinical benefit. When phlebotomy treatments are administered, however, blood volume should not be reduced too greatly at any one time, especially in patients with known arteriosclerotic symptoms (angina pectoris, transient ischemic attacks). This caution is particularly appropriate early in the course of therapy, when hematocrit (and consequent viscosity) are highest. Rather, time should be allowed for hemodilution to occur between phlebotomies; in emergencies, the blood volume should be maintained by infusing saline or some other plasma expander.
Diagnostic Approach to "Suspected Polycythemia Vera" - Mayo Clinic 2-1999
Hgb > 18.5 gm/dL, or a borderline elevated Hgb with any PV related feature, or an interim Hgb increase of > 2 gm/dL
Ref: Mayo Clin Proc, Feb 1999, 74: 159 - Ayalew Refferi
Relative Polycythemia (No elevated red cell mass)
Approach to erythrocytosis
A decrease in plasma volume may produce relative erythrocytosis. The decrease in plasma volume may result from any cause of intravascular fluid loss--insensible fluid loss, persistent vomiting, severe diarrhea, copious sweating, postoperative complications, or shift of fluid into the extravascular space ("third-spacing") or it may be an effect of high altitude. In severe burns, plasma loss leads to hemoconcentration.
Chronic relative polycythemia or erythrocytosis has been variously called
Gaisbock syndrome, stress erythrocytosis
, benign polycythemia or erythrocytosis, benign
erythrocytosis, spurious polycythemia,
pseudopolycythemia , or apparent
polycythemia. The last three terms are the most accurate: In the absence
of an increased red cell mass, there is no polycythemia.
Features reported to be strongly associated with relative polycythemia are stress, obesity, hypertension and smoking ; associations with alcohol abuse and renal disease are occasionally reported. It is probable that this syndrome is not a true clinical entity. The red cell mass values generally accepted as normal at sea level, or at any given altitude, represent the mean ± 2 standard deviations. Thus, on the basis of the normal frequency distribution curve for this physiologic parameter, the values in 2.3% of the population are above this range. The individuals in this group should not be regarded as necessarily abnormal.
The optimum management of relative polycythemia is unknown.
As noted previously, phlebotomy increases cerebral blood flow even in patients with relative polycythemia; whether it is of symptomatic benefit is less clear. It should probably be avoided.
Satisfactory control of hematocrit can be obtained in at least two-thirds of patients by reduction of excess weight, improved hypertension control, avoidance of diuretics, and reduction or cessation of smoking  .
Potentially leukemogenic cytoreductive therapy, such as radioactive phosphorus or oral chemotherapeutic agents, is probably never indicated.
Lee: Wintrobe's Clinical Hematology, 10th ed., Copyright © 1999