Highlights
- Hct was the right answer!😀 MCV varies between mammals independently of body size, and is inversely proportional to the RBC count, all in the name of achieving an evolutionarily conserved optimal Hb/Hct (Hct=MCV x RBC count) to optimize O2 delivery. MCH simply tracks with MCV. https://t.co/TVQCrB7snB
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- What do you prefer referring to: Hb or Hct?
I prefer using Hb in patients with anemia because oxygen carrying capacity is limiting, and Hct in patients with polycythemia because blood viscosity is limiting.
For those at equipoise, it's dealer's choice (though my bias is Hb)!
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- If blood is red, why do veins appear blue? It's an optical illusion! Blood is normally red because Hb preferentially reflects red light (oxyHb more so than deoxyHb). Blood in veins, by contrast, appears blue because skin scatters and returns more blue light than red to the eye.
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- Hyperglycemia and hyperNa cause falsely high MCV (spurious macrocytosis)?
But shouldn't water leave RBCs in a hypertonic environment, lowering the MCV?
In vivo, YES... but a CBC involves diluting patient RBCs 50,000-fold in isotonic solution, which they experience as hypotonic!
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- 25 yo F with Hb 9.6 and Hct 33.5. Is she compulsively eating non-food items? The chances are about 55%. Why? Because there is a violation in the 3:1 (Hct:Hb) rule, indicative of hypochromia = virtually diagnostic of iron deficiency, 55% of whom have pica #blood #hematology
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- Macrocytosis has a large differential diagnosis. One cause is an elevated retic count. An important clue in the CBC is a reduction in the MCHC since retics start off with a lower-than-normal MCHC, which then normalizes as they mature into smaller RBCs. #Hematology #Blood (View Tweet)
- Some define erythrocytosis as an elevation in RBC count. Accordingly, patients with thal minor and microcytosis qualify despite a normal Hb/Hct (Hct = RBC count x MCV). Not helpful! Erythrocytosis is an elevated red cell mass, as determined by the surrogates, Hb/Hct. #hematology (View Tweet)
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Hb or Hct?
I prefer using Hb in patients with anemia because oxygen carrying capacity is limiting, and Hct in patients with polycythemia because blood viscosity is limiting.
For those at equipoise, it's dealer's choice, though I like to think positively and use Hb. 😉
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