Hematocrit Notes

Hematocrit (HCT)

  • Defined as the percentage of red blood cells (RBCs) in the total blood volume.
  • Typically identified as part of a complete blood count (CBC), but can be tested separately.
  • CBC measures: Hematocrit, RBC count, white blood cell count, hemoglobin levels, and platelets.
  • Reference Ranges:
    • Adult males: 40% - 54%
    • Adult females: 36% - 48%

Importance of Hematocrit

  • Useful laboratory finding to indicate various medical conditions.
  • Too few RBCs may indicate anemia.
  • Too many RBCs may indicate polycythemia.
  • Can be used to monitor individuals post-operatively to screen for or prevent complications, such as internal bleeding.

Causes of Low Hematocrit Levels (Anemia)

  • May result from:
    • Decreased production of RBCs
    • Increased loss of blood
    • Increased destruction of RBCs
    • Combination of the aforementioned reasons
  • Common Causes:
    • Chronic blood loss (e.g., ulcers, colon cancer)
    • Acute blood loss (e.g., trauma, internal bleeding)
    • Menstruation (in females of reproductive age)
  • Peripheral destruction of RBCs:
    • Sickle cell anemia: RBCs have a shorter lifespan.
    • Splenomegaly: Enlargement of the spleen leads to the destruction of a greater number of healthy RBCs in the spleen.
  • Decreased production of RBCs:
    • Chronic inflammatory diseases
    • Bone marrow suppression (caused by radiation therapy, malignancies, or medications like chemotherapy)
  • Malnourishment:
    • Iron deficiency
    • Vitamin B12 deficiency
    • Folate deficiency
  • Overhydration

Causes of High Hematocrit Levels

  • May result from:
    • Hemoconcentration
    • Overproduction of RBCs
  • Hemoconcentration:
    • Dehydration (due to fluid loss from repetitive vomiting, overheating, or limited access to fluids)
  • Low oxygen availability:
    • Triggers the production of new blood cells to transport oxygen.
    • Caused by smoking, high altitudes, congenital heart diseases, or certain pulmonary disorders such as pulmonary fibrosis or COPD.
  • Polycythemia vera:
    • Characterized by the overproduction of RBCs.
  • Increased erythropoietin production
  • Endocrine system conditions:
    • Cushing's syndrome