A special thank you to Dr. Lee Levitt for coming to morning report to participate in this interesting case!

Teaching Pearls:

• Discrepancy of a low O2sat along with normal PaO2 is classically seen with methemoglobinemia.
  • Other causes include poor perfusion state such as vasoconstriction, hypothermia, or any other conditions that cause poor flow state.
  • Methemoglobin – Iron within hemoglobin exists as the oxidized state (+3), causing decreased affinity for oxygen binding.
• Carboxyhemoglobin – when carbon monoxide binds to hemoglobin.
  • Hemoglobin has a very high affinity for CO compared to O2. Causes the oxygen dissociation curve to shift to the left, leading to decreased ability for O2 unloading.
  • Pulse oximetry cannot distinguish between carboxyhemoglobin and oxyhemoglobin.
• Workup of anemia
  • Underproduction
  • Blood loss
  • Increased destruction (hemolysis)
• Reticulocyte count – important to correct for degree of anemia and time of maturation.
  • High corrected reticulocyte index suggestive of blood loss or hemolysis.
  • Low corrected reticulocyte index suggestive of underproduction.
• Hemolysis Labs
  • High LDH, low haptoglobin, indirect hyperbilirubinemia, Coombs test
• Blood Smear
  • Schistocytes, helmet cells suggestive if microangiopathic hemolytic anemia.
  • Bite cells and Heinz bodies suggestive of G6PD deficiency.
  • Spherocytosis suggestive of either hereditary spherocytosis or autoimmune hemolytic anemia.
  • Sickle cells suggestive of sickle cell anemia
  • Target cells suggestive of liver disease (in particular obstructive liver disease), hemoglobinopathy, etc
• Causes of Intrinsic hemolysis
  • RBC membrane defects
    • Example includes hereditary spherocytosis
  • Hemoglobinopathy
    • Examples include thalassemia, sickle cell disease, etc
  • Oxidation Problem
    • Most common example is G6PD deficiency.
• G6PD Deficiency
  • Different variants of disease spectrum
  • X-linked disease – manifest in males
  • Hemolysis precipitated by acute insult, including infections or medications.
  • Medications associated with hemolysis include primaquine, dapsone, sulfa medications, etc.
  • Mediterranean variant associated with favism.
  • Negative G6PD test does not rule out G6PD deficiency in the setting of hemolysis.