Experiences with the Radiochromium method for Determination of Red Cell Volume

Abstract

We have described in detail a modification of Sterling and Gray's Cr⁵¹ method for blood volume determination with which we have had considerable experience. The dose of Cr⁵¹ needed for tagging 12 ml of the patient's blood need not exceed 50—75 μC if a well-type scintillation counter is used. The tagged cell suspension is usually stored overnight so that the test can he done conveniently before breakfast. The cells are delivered from a small infusion apparatus through an indwelling needle which is also used for sampling. The over-all error of the measurement of cell volume, as shown by repeating the test after intervals of 3 to 31 weeks, averages 3.9 per cent. This compares favorably with results obtained with other modifications of the Cr⁵¹ method and with P³², even though the long time interval between tests in this study allowed the possibility of within-subject changes of cell volume. The major sources of error are a) the determination of radioactivity of blood specimens and tagged cell suspension, and b) determination of the centrifuged hematocrit, particularly with respect to the percentage of trapped plasma iii the cell column. Failure to measure accurately the volume of tagged cell suspension delivered to the subject, a serious potential source of error, proved to be relatively unimportant with the technique used. Errors relating to the collection and handling of blood for hematocrit determinations and in the prediction of the “body hematocrit: venous hematrocrit ratio can materially affect the estimation of blood and plasma volumes, but not cell volume.