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Riddle me this: (good question posed by a medical student)
In an acutely bleeding patient, we often note a dropping Hgb in a series of CBCs (12 g/dL --> 10 --> 8, etc).
But this measured value from the CBC is a concentration of Hgb (g/dL), not a total amount.
It makes sense that the total amount of Hgb (or the total amount of blood volume) would drop in a bleeding patient, but why would the concentration change so abruptly? Shouldn't the concentration remain fairly constant? [If you had 10 L of sugar water of a certain concentration, 2 molar, then you drained out 5 L, the new concentration should be the same, 2 molar. total amount of sugar is decreased, but concentration, assuming uniformly dissolved, is the same.]
Or, is it the case that the Hgb we're getting from a CBC is not a true concentration, but some number more reflective of the total Hgb in the body?
In an acutely bleeding patient, we often note a dropping Hgb in a series of CBCs (12 g/dL --> 10 --> 8, etc).
But this measured value from the CBC is a concentration of Hgb (g/dL), not a total amount.
It makes sense that the total amount of Hgb (or the total amount of blood volume) would drop in a bleeding patient, but why would the concentration change so abruptly? Shouldn't the concentration remain fairly constant? [If you had 10 L of sugar water of a certain concentration, 2 molar, then you drained out 5 L, the new concentration should be the same, 2 molar. total amount of sugar is decreased, but concentration, assuming uniformly dissolved, is the same.]
Or, is it the case that the Hgb we're getting from a CBC is not a true concentration, but some number more reflective of the total Hgb in the body?