Although this will likely not result in life-or-death decisions and is more a matter of intellectual curiosity, I would argue that hemoglobin is superior to hematocrit because it is directly measured and tells you about O2 delivery. Read on.
Hemoglobin is directly measured with spectroscopy (it’s a pigmented dye, so can be directly measured).
Hematocrit can be measured, but in modern times is calculated (RBC count x MCV). It represents a ratio of packed cells: total volume. Conditions that change the osmolarity of the blood will change the MCV temporarily, and affect Hct. It is affected by multiple factors:
- Polycythemic or macrocytic anemias (larger MCV but less number of RBCs may show a normal Hct but low Hgb)
- Microcytic anemias would show a reduced MCV and reduced RBC count, so the Hct should still be in line with the reduced Hgb
Hyperosmolar (falsely lowering the Hct):
- Recent blood transfusion
Hypoosmolar (falsely elevating the Hct):
- High altitude
- Recent hemorrhage
I’ve been told you shouldn’t order both Hgb and Hct, but you want to analyze RBC indices correctly, I think it’s necessary, as these depend on both Hgb and Hct.