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Is there a standard plasma/blood volume ratio in normal humans? I need
this information for pharmacokinetic studies.
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A good measure of blood cell volume as a percent of blood volume is
the hematocrit which is the fraction of blood volume occupied by red
blood cells. Hematocrit is usually expressed as a percent. The plasma volume
is equal to (1-hematocrit) X 100%.
The normal hematocrit for adults is approximately 41-53% for males
and 36-46% for females. Values for children and references for these
values can be found in any laboratory medicine text or hematology
reference book. Also, all clinical laboratories have their normal
ranges.
This would provide an approximate plasma:whole blood ratio of
(1-0.47) x 100% = 53% for adult males and (1-0.41) x 100%= 59% for
adult females. You may even consider measuring hematrocit in your
samples to provide more accurate individual values.
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It seems that you are after a value for "plasmacrit" (the fractional
volume of plasma to whole blood), which is
1-hematocrit or about 1-0.45 in normals (ca., 0.55).
Michael Mayersohn
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Tom:
You should be able to determine the volume of plasma per unit volume of
blood by determining the hematocrit and leukocrit for a particular sample
by adding the Hct and Lct values for that sample. The hematocrit and
leukocrit (usually expressed as a percentage) account for the predominant
cellular elements present in whole blood. The portion remaining is plasma.
e.g., if...
(hematocrit [%] + leukocrit [%]) x (blood sample volume) = volume occupied
by cells
then...
(blood sample volume) - (volume occupied by cells) = plasma volume
In clinical practice, one derives a very reasonable estimate of plasma
volume from hematocrit alone, the volume occupied by leukocytes and
platelets are not considered.
Dave
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Blood Volume = Plasma Volume / (1 - Hct) Where: Hct = hematocrit fraction
Thus if Hct = 0.45, and Plasma Volume = 3.2 L, the
Blood Volume = 3.2/0.55 = 5.820 L
Plasma Volume is determined using an albumin-bound dye (Evans Blue) or
131I-albumin.
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Unless there is something subtle here that you have not mentioned in
your short post, the ratio of plasma volume to blood volume is
1 - Hct. The hematocrit is typically 0.45 so the ratio you asked for is
about 0.55.
If you need something more complex than this, please repost to the list.
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