Jan

14

2025

Effects of CLL on Red Cell Parameters

By William Aird

  • Red blood cell (RBC) histogram:
    • RBC histogram is used to measure/calculate:
      • RBC count
      • Mean cell volume (MCV)
      • Red cell distribution width (RDW)
    • Most hematology analyzers use impedance to count and characterize RBCs, identified by volume cut-offs.
    • Lymphocytes, the smallest of the white blood cell (WBC) subtypes, have a reported mean volume of:1
      • 166 +/- 19.3 (range 126-216) fL in normal individuals
      • 206 +/- 14.4 (range 126 +/- 246) in patients with CLL
    • Some of the lymphocytes are small enough to be counted in the RBC gate.
    • Normally, there are so few lymphocytes relative to the number of RBCs that they do not affect the results even if a few are included in the RBC analysis.
    • In chronic lymphocytic leukemia (CLL), hyperleukocytosis may result in a bimodal population (RBCs and lymphocytes) resulting in an artificial elevation in the MCV (pseudo-macrocytosis) and RDW.
  • Other red cell indices:
    • Mean corpuscular hemoglobin (MCH) is calculated as hemoglobin/RBC count:
      • Hemoglobin is unaffected by the presence of WBCs.
      • The RBC count is only marginally affected because they far outnumber the lymphocytes, even in cases of hyperleukocytosis.2
      • Because the Hb is unaffected and the RBC count only slightly affected, the MCH is only minimally affected.3
    • Mean corpuscular hemoglobin concentration (MCHC) is calculated as Hb/Hct:
      • The Hb is not affected by hyperleukocytosis.
      • In most automated analyzers, the Hct is derived from the MCV and RBC count (Hct – RBC count x MCV).
      • Because the MCV is disproportionally affected (increased) relative to a change in the RBC count, the MCHC is decreased in such cases.