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Question 342
Physiology → Haematology
Classification
Question
SSBAQuestion Header
A woman has a measured plasma volume of 3.0 L and a haematocrit of 0.40.
Question Stem
What is her calculated blood volume?
Options
A
4.2 L
B
5.0 L
C
5.5 L
D
6.0 L
E
7.5 L
Explanation
Blood volume is calculated as plasma volume divided by (1 − haematocrit). Therefore, BV = 3.0/(1 − 0.40) = 3.0/0.60 = 5.0 L.
Option Validity
A) 4.2 L does not result from dividing the plasma volume by the non-cellular fraction of blood.
C) 5.5 L is greater than the value obtained using BV = PV/(1 − HC).
D) 6.0 L is not obtained when a plasma volume of 3.0 L and haematocrit of 0.40 are substituted into the formula.
E) 7.5 L substantially overestimates blood volume for the supplied plasma volume and haematocrit.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Blood, p.67.