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  • Affects 1/3 of the world's population
  • Most common causes are uterine and GI bleeding


4 mechanisms:

  1. Loss of RBCs by hemorrhage (e.g. GI bleed)
  2. Increased destruction (SCD, hemolytic anemia)
  3. Impaired production (iron deficiency, folate deficiency, B12 deficiency, aplastic anemia/myelodysplastic syndrome)
  4. Dilutional (rapid IVF infusion)

Clinical Features

General Anemia Symptoms

  • Most patients begin to be symptomatic at ~7gm/dL
  • Weakness, fatigue, lethargy, dyspnea on exertion, palpitations
  • Skin, nail bed, mucosal pallor
  • Widened pulse pressure
  • Jaundice, hepatosplenomegaly (hemolysis)
  • Peripheral neuropathy (B12 deficiency)

Differential Diagnosis


RBC Loss

  • Hemorrhage

RBC consumption (Destruction/hemolytic)

Impaired Production (Hypochromic/microcytic)

  • Iron deficiency
  • Anemia of chronic disease
  • Thalassemia
  • Sideroblastic anemia

Aplastic/myelodysplastic (normocytic)

  • Marrow failure
  • Chemicals (e.g. ETOH)
  • Radiation
  • Infection (HIV, parvo)

Megaloblastic (macrocytic)

  • Vitamin B12/folate deficiency
  • Drugs (chemo)
  • HIV


Severe anemia is defined as a hemoglobin level of 5 to 7 g/dL with symptoms of hypoperfusion including lactic acidosis, base deficit, shock, hemodynamic instability, or coronary ischemia[1]

Acute Anemia

Assess for any signs of bleeding or trauma before considering other causes of chronic anemia.

Algorithm for the Evaluation of Anemia

Chronic Anemia

Microcytic Anemia (<81 fL)

  • RDW high
    • Ferritin low: Iron deficiency anemia
    • Ferritin normal: Anemia chronic disease or sideroblastic anemia (e.g. lead poisoning)
  • RDW normal
    • RBC count low: Anemia chronic disease, hypothyroidism, Vitamin C deficiency
    • RBC count nl or high: Thalassemia

Normocytic Anemia (81-100 fL)

  • Retic count normal
    • RDW normal: Anemia chronic disease, anemia of renal insufficiency
    • RDW high: Iron, Vit B12, or folate deficiency
  • Retic count high
    • Coombs Positive: Autoimmune cause
    • Coombs negative: G6PD, SCD, spherocytosis, microangiopathic hemolysis

Macrocytic Anemia (MCV>100 fL)

  • RDW high: Vit B12 or folate deficiency
  • RDW normal: ETOH abuse, liver disease, hypothyroidism, drug induced, myelodysplasia


  • Transfusions
    • Consider if patient is symptomatic, hemodynamically unstable, hypoxic, or acidotic
    • Most patients with hemoglobin <6 will benefit from transfusion; most patients with hemoglobin >10 will not
    • Always draw labs necessary for diagnosis prior to transfusing
    • 1 unit PRBCs should raise the Hgb by 1gm/dL

See Also

External Links


  1. Posluszny JA Jr, Napolitano LM. How do we treat life-threatening anemia in a Jehovah's Witness patient? Transfusion. 2014;54(12):3026-3034