Anemia

General

  • Neonates have a physiologically higher-than-adult haemoglobin (Hb) at birth
    • Falls to lower-than-adult numbers at 3-6 months
    • Rises gradually there after until reaching adult values again by the early teenage years
  • Anemia of premature babies:
    • Premature Infant: more rapid decline and lower Hgb than term
    • 40% infants <33 weeks show symptoms of anemia
  • Adult females have a lower Hb than adult males, on average
  • Hb tends to fall in the elderly
    • Do not investigate mild degrees of anemia in the elderly

Classification

  • A pathophysiological classification of anemia: All anemias are due to:
    • Under-production of erythrocytes
    • Excessive loss or destruction of erythrocytes
    • Dilution due to an increased plasma volume
  • A diagnostic classification of anemia: based on mean corpuscular volume (MCV)
    • Reduced is referred to as: microcytic
    • Increased is referred to as: macrocytic
    • The same size is referred to as: normocytic

Microcytic Anemia

  • The most important causes are:
    • Iron deficiency
    • Hemoglobinopathies, especially thalassemia
    • The ‘anemia of chronic disease’ (some cases only)
  • The most important diagnostic measurement is the serum ferritin
    • In uncomplicated iron deficiency, the ferritin is low
    • In other microcytic anemias the ferritin is normal. *When iron deficiency is accompanied by some other chronic disease process (e.g. rheumatoid arthritis), the serum ferritin may be spuriously normal
    • The ‘gold standard’ for the assessment of iron stores is the bone marrow aspirate
      • Rarely necessary

Macrocytic Anemia

  • These may be classified into
    • Megaloblastic:
      • Bone marrow erythropoiesis has a specific morphological abnormality called megaloblastosis
      • For patients who are not on cytotoxic drugs, usually indicates a deficiency vitamin B12 or folic acid
      • A bone marrow aspirate is not always necessary, as the presence of the following is highly suggestive of a megaloblastic process:
        • Oval macrocytes
        • Hypersegmented neutrophils
      • A serum vitamin B12 and folate estimation can then often make the diagnosis
    • Non-megaloblastic:
      • There are a large number:
        • Alcohol
        • Hypothyroidism
        • Liver disease
        • Others
 

Normocytic Anemia

  • These may be classified using the reticulocyte count as follows:
    • Low Reticulocytes (underproduction of erythrocytes)
      • The anemia of chronic disease
      • Marrow failure
      • Renal failure (decreased erythropoietin)
    • Increased Reticulocytes (increased marrow output of erythrocytes)
      • Hemolysis
      • Blood loss (acute only)

Anemia of Chronic Disease

  • Seen in:
    • Cancer
    • Infection
    • Inflammation
  • Commonly have a mild-to-moderate anemia caused by red cell underproduction
  • Common, and is usually normocytic
    • Some cases develop abnormalities of iron metabolism resulting in a secondary microcytosis.
 

Hemolysis

  • Premature destruction of red blood cells, from whatever cause.
  • Markers of a hemolytic process:
    • Raised reticulocyte count
    • Decreased serum haptoglobin concentration
    • Raised Lactate Dehydrogenase (LDH)
  • A Direct Coombs’ Test:
    • Tests whether RBCs are antibody-coated
    • Indicates an immune-mediated hemolytic process
    • Note: some patients with a positive Direct Coombs’ Test do not have hemolysis
  • The principal causes of hemolysis :
     
    • Inherited abnormalities of:
      • Membrane
        • Congenital Spherocytosis
      • Hemoglobin
        • Sickle Cell Anemia)
      • Enzymes
        • Glucose-6-phosphate dehydrogenase deficiency
       
    • Acquired causes:
      • Immune
        • Warm Autoimmune Hemolytic Anemia
      • Non-immune
        • E.g. Red cell damage from leaky heart valve, drugs, infections

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