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#1
12-24-2012
 USMLE Forums Guru Steps History: Not yet Posts: 315 Threads: 115 Thanked 155 Times in 84 Posts Reputation: 165
Understanding the Hematocrit Percentage

I feel embarassed to ask this, because this is basic info. i thought i knew this, until i opened up a physio book.

Plasma = 55% of blood volume

that means the other 45% is taken up by blood cells (rbc, wbc, platlets)

this confused me a little, because i know that hematocrit averages around 45%. so this is 45% of the 45% that does not include plasma volume, right? sorry if my question is confusing.

in other words, the hematocrit of 45%, what is this percentage based on? surely it can't be based on total blood volume.

#2
12-24-2012
 USMLE Forums Guru Steps History: Not yet Posts: 315 Threads: 115 Thanked 155 Times in 84 Posts Reputation: 165

click to enlarge

The figure above makes my question easier to understand:

I understand plasma = 55% blood volume

I understand that formed elements = 45% blood volume

but how does a hematocrit of 45% factor in?

hematocrit is volume of packed RBC's. according to the image above, it should average LESS THAN 45%, to factor out the 'formed elements' contributed by WBC's and platelets.

What am I missing here?
#3
12-24-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 824 Threads: 66 Thanked 462 Times in 298 Posts Reputation: 472

As u can see from picture formed elements other than rbcs make very tiny sediment which compared to rbcs are literally insignificant when measuring htc
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#4
12-24-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 304 Threads: 48 Thanked 291 Times in 106 Posts Reputation: 301

hematocrit is everything besides plasma not just rbcs
#5
12-24-2012
 USMLE Forums Guru Steps History: Not yet Posts: 315 Threads: 115 Thanked 155 Times in 84 Posts Reputation: 165

Quote:
 Originally Posted by MedicalExaminer As u can see from picture formed elements other than rbcs make very tiny sediment which compared to rbcs are literally insignificant when measuring htc
sounds good, thanks
#6
12-24-2012
 USMLE Forums Guru Steps History: Not yet Posts: 315 Threads: 115 Thanked 155 Times in 84 Posts Reputation: 165

Quote:
 Originally Posted by obinocle hematocrit is everything besides plasma not just rbcs
i'm pretty sure its the RBC volume
#7
12-25-2012
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 304 Threads: 48 Thanked 291 Times in 106 Posts Reputation: 301

Quote:
 Originally Posted by ReggieMiller i'm pretty sure its the RBC volume

 Tags Figures-, Hematology-, Physiology-

Message:
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