Hematocrit Notes

Hematocrit

  • Used to diagnose and monitor conditions like rheumatoid arthritis, anemia, and cancers.
  • Definition: Percentage of red blood cells in a volume of whole blood.
  • Measured by centrifuging a blood sample.
    • Red blood cells (RBCs) settle at the bottom.
    • Plasma remains on top.
    • Buffy coat (leukocytes and platelets) is between plasma and RBCs.
  • Procedure:
    • Fill a heparinized capillary tube 34\frac{3}{4} full with blood.
    • Seal the end with capillary tube sealer.
    • Centrifuge.
    • Measure the height of packed RBCs and total blood sample in millimeters.
    • Calculate hematocrit percentage: (RBC heightTotal blood height×100)(\frac{RBC \, height}{Total \,blood \,height} \times 100)
  • Normal Hematocrit Ranges:
    • Males: 42-52%
    • Females: 37-47%
  • Factors Affecting Hematocrit:
    • Dehydration: Can falsely elevate hematocrit due to decreased plasma volume.
    • Overhydration: Can falsely lower hematocrit due to increased plasma volume.
    • Pregnancy: Can slightly decrease hematocrit due to hemodilution.

Anemia and Polycythemia

  • Anemia: Low oxygen carrying capacity of blood, potentially due to low hematocrit. Several types exist, including:
    • Iron-deficiency anemia: Caused by insufficient iron for hemoglobin synthesis.
    • Vitamin deficiency anemia: Lack of vitamin B12 or folate.
    • Hemolytic anemia: Premature destruction of red blood cells.
  • Polycythemia: Abnormally high hematocrit (too many red blood cells).
    • Primary polycythemia (Polycythemia vera): A genetic mutation causing increased RBC production.
    • Secondary polycythemia: Often due to chronic hypoxia or EPO-secreting tumors.

Erythropoietin (EPO)

  • Hormone that stimulates erythropoiesis (RBC synthesis).
  • Released by kidney cells when oxygen delivery is low.
  • Synthetic EPO: Used to treat anemia but is also misused in blood doping.

Gender Differences in Hematocrit

  • Testosterone enhances kidney production of EPO, resulting in higher RBC counts in males.
    • Androgens stimulate RBC production.

Secondary Polycythemia

  • Develops at high altitudes due to lower oxygen content, stimulating EPO production and increasing hematocrit.
    • Adaptation to lower oxygen levels.

Blood Doping

  • Increases oxygen carrying capacity by increasing RBC count.
  • Methods:
    • EPO injections
    • Blood transfusions
  • Risks: Increased blood viscosity, heart problems, stroke.

Calculating Hematocrit

  • Hematocrit=(Length of Red Blood Cells (mm)Length of Whole Column (mm)×100)Hematocrit = (\frac{Length \,of \,Red \,Blood \,Cells \,(mm)}{Length \,of \,Whole \,Column \,(mm)} \times 100)