A blood-volume determination was carried out on a patient by injection with 20.0
ID: 960033 • Letter: A
Question
A blood-volume determination was carried out on a patient by injection with 20.0 mL of blood that had been radioactively labeled with Cr-51 to an activity of 4.10 microCi/mL. After a brief period to allow for mixing in the body, blood was drawn from the patient for analysis. Unfortunately, a mixup in the laboratory prevented an immediate analysis, and it was not until 17.0 days later that a measurement on the blood was made. the radiation level was determined to be .00935 microCi/mL. If 51Cr has t1/2=27.7 days, what is the volume of blood in the patient?
Explanation / Answer
A = A0e-t ;
Where A= activity in time t
A0= initial activity at t=0
= 0.693/ t1/2 = 0.693/ 27.7 = 0.0250 day-1
According to the formula;
T = - / ln (A/ A0)
17.0 = - 0.0250 / 2.303 log ( .00935 x V / 4.10 x 20),
where V= volume of blood in the patient
V= 8757.168 ml
V = 8757.168 ml (Volume of blood in the body)
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