Anemia

Basics

Description

  • Reduction below normal in the mass of red blood cells (RBCs)
  • Measured by 1 or more of the major RBC components:
    • Hemoglobin (Hgb): Concentration of the major oxygen-carrying component in whole blood
    • Hematocrit (Hct): Percent volume of whole blood occupied by intact RBCs; calculated so less likely to be accurate than Hgb
    • RBC count: RBCs contained in a volume of whole blood
  • Adult female: Hgb <11.5 g/dL or Hct <35%
  • Adult male: Hgb <13.5 g/dL or Hct <40%
  • Normal blood count values depend on age:
    • Birth: Hgb 16.6, Hct 53
    • 1 yr: Hgb 12.7, Hct 37
    • 6 yr: Hgb 12.5, Hct 37
    • Adult male: Hgb 13.5, Hct 40
    • Adult female: Hgb 11.5, Hct 35
  • Hgb/Hct depend on oxygen pressure:
    • Increased in neonates and people living above 4000 ft
  • Hgb, Hct, and RBC count are concentrations:
    • Dependent on RBC mass and plasma volume
    • Values decrease if RBC mass decreases or plasma volume increases
    • Hgb and Hct decrease in parallel although the Hgb:Hct ratio may vary according to the volume (size) of the cells
  • Anemia is an indication of an underlying disorder or deficiency

Etiology

  • Never a normal variant:
    • May be the first manifestation of a systemic disorder
    • Always seek a cause
  • Excessive blood loss (most common cause):
    • Trauma
    • Gastrointestinal bleed (GIB)
    • Menstruation
  • Hemolysis (increased RBC destruction, RBC lifespan <100 d):
    • Hypersplenism
    • Autoimmune hemolytic anemia
    • Mechanical trauma (prosthetic heart valves, vasculitis, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, or disseminated intravascular coagulation)
    • Toxins
    • Infections (malaria, babesiosis)
    • Membrane abnormalities
    • Intracellular RBC abnormalities (G6PD, sickle cell anemia, or thalassemia)
  • Decreased RBC synthesis; classified by measurement of RBC size:
    • Hypochromic/microcytic:
      • Iron deficiency (late)
      • Thalassemia
      • Sideroblastic
      • Lead poisoning
      • Chronic disease (less likely)
    • Normochromic/macrocytic:
      • Hypothyroidism
      • Folate deficiency
      • Vitamin B12 (cobalamin) deficiency
      • Liver disease
      • Myelodysplasia
      • Certain leukemias
      • Medications
    • Normochromic/normocytic:
      • Iron deficiency (early)
      • Aplastic anemia
      • Chronic disease/chronic renal failure
      • Malignancy
      • Adrenal insufficiency
      • Hyperparathyroidism
      • Alcohol abuse
      • Acute blood loss

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