Polycythemia

Q: What is the difference between relative, absolute, primary, and secondary polycythemia?

Answer: By definition, polycythemia means an elevation in the values of hemoglobin (Hb) and/or hematocrit (Hct). The accepted cut-off points are:

• Hb:  >16.5 g/dL in men or >16.0 g/dL in women
• Hct:  >49% in men or >48% in women

Various factors may affect these values.

Relative polycythemia is basically hemoconcentration due to decrease in plasma volume alone. It means there is no real increase in RBC mass.

Absolute polycythemia is an actual increase in RBC mass. It is further divided into primary and secondary polycythemia.

Primary polycythemia is due to a mutation in RBC progenitor cells. In contrast, secondary polycythemia, as the name implies, is secondarily elevated serum erythropoietin for various reasons, such as smoking or living at high altitudes.

#hematology

References:

1. Pillai AA, Fazal S, Babiker HM. Polycythemia. 2022 Jul 10. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30252337.

2. Ayalew Tefferi - Diagnostic approach to the patient with polycythemia: © 2022 UpToDate : Link: https://www.uptodate.com/contents/diagnostic-approach-to-the-patient-with-polycythemia (Last accessed:: November 18, 2022)