THE USE OF K42 OR P32 LABELED ERYTHROCYTES AND I131 TAGGED HUMAN SERUM ALBUMIN IN SIMULTANEOUS BLOOD VOLUME DETERMINATIONS 1

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Abstract
Simultaneous blood volume detns. utilizing albumin tagged with I131 and erythrocytes tagged with p32 or K42 have been performed in 25 tests on 21 human subjects. In every instance, the whole blood volume evaluated by the tagged albumin dilution was greater than that derived from the dilution of the tagged erythrocytes. The avg. body hematocrit/peripheral vessel hematocrit ranged from 0.860-0.996 with a mean value of 0.924. Since whole blood samples were assayed, these ratios did not depend on the accuracy of the observed hematocrit reading. Arterial mixing curves revealed that apparent equilibrium may not be attained until 5-10 min. after injn. although the concns. at 1-1.5 min. are only approx. 10% above the equilibrium values. There is no essential difference in the mixing times of tagged albumin and erythrocytes. Albumin tagged with I131 is a satisfactory material for the estimation of circulating plasma volume. Owing to the difference between avg. body hematocrit and peripheral vessel hematocrit the accurate evaluation of whole blood volume requires independent detns. of plasma and red blood cell volumes.