LabMed

Elevated Hemoglobin or Hematocrit

Differential Diagnosis

Pt with true polycythemia with an increased red blood cell (RBC) mass.

Pt with a relative polycythemia and a normal RBC mass as a result of dehydration or another state producing a low plasma volume.

Dangerous Situations

Polycythemia in which the RBC mass is high enough to impair blood flow.

Commonly Encountered Situations

Polycythemia vera, also known as primary polycythemia, is not secondary to any disorder.

Polycythemia from an underlying disorder (secondary polycythemia) is much more common than primary polycythemia.

Suggested Additional Lab Testing

Serum erythropoietin level is low in primary polycythemia, unlike secondary polycythemia, so the erythropoietin (EPO) level can be useful in separating primary and secondary polycythemia.

Strict criteria are required for the diagnosis of polycythemia vera: (A1 plus A2 plus any other A) or (A1 plus A2 plus any 2B) criteria:

  • Increased RBC mass by hemoglobin, hematocrit, or RBC number (A1)

  • Erythrocytosis is not secondary to another cause (A2)

  • Splenomegaly (A3)

    1. Clonal cytogenetic abnormality other than the Philadelphia chromosome (A4)

    2. Endogenous erythroid colony formation in vitro (A5)

  • Platelet count greater than 400,000/µL (B1)

  • WBC count greater than 12,000/µL (B2)

  • Panmyelosis on bone marrow biopsy (B3)

  • Low serum EPO (B4)

Bone marrow biopsy may be useful to determine if polycythemia vera is in a hypercellular phase with greater than 60% cellularity or in a hypocellular bone marrow with markedly increased reticulin fibers.

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