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The CBC, loved by surgeons, hated by everyone else.  Really it’s the WBC count that is so controversial.  But many of us don’t know some of the subtle but important aspects of the CBC that we may or may not have learned in medical school but have forgotten.

  • Automated Diff: Routinely done by Coulter counter when stream of cells passes through a spectrometer.  Can pick up bands, blasts, and abnormal RBC morphology, such as schistocytes
  • Manual Diff: Only done if ordered or there are red flags on the automated diff, which may vary by hospital but typically includes some of the following: abnormal RBC morphology, bands >11%, or blasts.  Elevated WBC count alone does NOT usually trigger a manual dif.

If you are not facile with the differential, toxic granulationDohle bodies, vacuoles, and atypical lymphs read below because YOU SHOULD BE!

You should also be aware that RBC morphology showing Howell-Jolly bodies can signify hyposplenism, leukemia, thalassemia, or pernicious anemia and the first two of these are associated with decreased immunity.  Also RBC Pappenheimer bodies: can signify splenectomy, MDS, sickle cell disease, sideroblastic anemia, hemolysis or lead poisoning, the first three of which can be associated with decreased immunity

Another useful strategy is how to handle an elevated WBC count thatyou don’t think is critical and is just due to demargination.  These WBC counts will usually be between 11-16, although they can be higher.  I usually order a Sed rate and a CRP.  If either or both of these are both normal, you can probably blow off the elevated WBC count.  If you only order one, the CRP is probably more sensitive


Pain, anxiety, trauma, pregnancy or any form of emotional or physiologic stress can cause any or all of the following lab abnormalities, probably from endogenous adrenaline release and/or hyperventilation

  1. Leukocytosis from demargination (often left shift but should not have toxic granulation or Dohle bodies and CRP should be normal)
  2. Hyperglycemia
  3. Hypokalemia from shift into cells similar to giving albuterol for hyperkalemia
  4. Low bicarb non-gap metabolic acidosis to compensate for respiratory alkalosis (hyperventilation).  This probably starts within minutes but is only remarkable if hyperventilation has been going on for more than half an hour (my estimate)