Bleed vs dilutional drop in Hgb

[waterbottle10]

Stupid question but why does only Hgb drop in bleeding, but when all drops, it points toward dilutional? I understand how if blood is diluted, everything drops. When we loose blood, don't we lose everything since blood has wbc and platelets as well? My understanding is that initially with bleed, there isn't much change in Hb since Hb is measured in concentration, and blood lost is the same concentration, so blood remaining is still the same concentration. It's only after giving/drinking fluids, or fluid shift that Hgb drops. But if that's the case, bleeding would be a form of dilutional as well, so all (WBC/RBC) should drop?

Can someone correct this understanding please.

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[shiftingmirage]

Maybe rate of production?
RBCs last ~3 months, neutrophils last hours to days, platelets last ~10 days.
At baseline neutrophils and platelets are produced at a higher rate and can recover quicker. In an acute bleed, there may also be some demarginiliation recruiting WBCs.

 

[waterbottle10]

Maybe rate of production?
RBCs last ~3 months, neutrophils last hours to days, platelets last ~10 days.
At baseline neutrophils and platelets are produced at a higher rate and can recover quicker. In an acute bleed, there may also be some demarginiliation recruiting WBCs.

maybe in subacute range? but for acute bleeds, i doubt neutrophil and platelet is produced that quickly? demargination possibly for neutrophils.. but not sure why in acute bleed hgb drops lot more than others

 

[DoctwoB]

Stupid question but why does only Hgb drop in bleeding, but when all drops, it points toward dilutional? I understand how if blood is diluted, everything drops. When we loose blood, don't we lose everything since blood has wbc and platelets as well? My understanding is that initially with bleed, there isn't much change in Hb since Hb is measured in concentration, and blood lost is the same concentration, so blood remaining is still the same concentration. It's only after giving/drinking fluids, or fluid shift that Hgb drops. But if that's the case, bleeding would be a form of dilutional as well, so all (WBC/RBC) should drop?

Can someone correct this understanding please.

Short answer: the premise is incorrect.

Long answer: All 3 cell lines can and will drop in very acute bleeding with time for fluid shifts and resuscitation. Platelets and WBC are more variable, however because often acute bleeds are associated with a stress response that leads to WBC demargination and release of WBCs and platelets from the BM. note that this is not production of new cells, which takes a much longer time, but rather release of pre-existing neutrophils, bands, precursors, etc. Despite this, platelets still tend to drop quite precipitously from consumption due to ongoing thrombosis.

 

[nycscope]

Quick cheat: look at albumin and creat trends. Nobody's albumin goes from 4 to 3 and creat from 2 to 1 without some help from not-so-normal saline (my least favorite fluid).

 

[Crayola227]

I might be way off base but for some reason I thought the spleen could act as a repository for RBCs and WBCs and platelets and do a lot to compensate for acute blood loss.

My guess with a bleed is that one isn't losing much by way of WBCs and platelets because those have better "grip" to them then the RBCs. An image of a space show where a room is vented to space and everything gets sucked out but the people holding on to something.

Then I imagine plts and WBCs being mobilized from reserve areas, of which the reserve to draw on is greater/faster than that of RBCs.

Or I made this all up.