Red Cell Volume Determination Using a Stable Isotope of Chromium

Red blood cell (RBC) survival determined in humans using RBCs labeled at multiple biotin densities

BACKGROUND

Safe, accurate methods permitting simultaneous and/or repeated measurement of red blood cell (RBC) survival (RCS) are important to investigate pathophysiology and therapy of anemia. Methods using chromium 51 ((51) Cr)-labeled RBCs are unacceptable for infants, children, and pregnant women. We report RCS measured in vivo using RBCs labeled with several densities of biotin (BioRBCs).

STUDY DESIGN AND METHODS

Aliquots of autologous RBCs from eight healthy adult subjects were labeled separately at four discrete biotin densities, mixed, and infused. The proportion of each population of BioRBCs circulating was determined serially by flow cytometry over 20 weeks. For each population, RCS was assessed by the following: 1) posttransfusion BioRBC recovery at 24 hours (PTR(24) ); 2) time to decrease to 50% of the enrichment at 24 hours (T(50) ); and 3) mean potential lifespan (MPL).

RESULTS

Among the four BioRBC densities, no significant differences in PTR(24) were observed. T(50) and MPL were similar for the two lowest BioRBC densities. In contrast, the two highest BioRBC densities demonstrated progressively decreased T(50) and MPL.

CONCLUSIONS

RBCs labeled at four biotin densities can be used to independently and accurately measure PTR(24 ) and two lowest biotin densities can accurately quantitate long-term RCS. This method provides a tool for investigating anemia in infants, fetuses, and pregnant women with the following advantages over the standard (51) Cr method: 1) study subjects are not exposed to radiation; 2) small blood volumes (e.g., 20 µL) are required; and 3) multiple independent RCS measurements can be made simultaneously in the same individual.

Comparison of total blood volume in normal, preeclamptic, and nonproteinuric gestational hypertensive pregnancy by simultaneous measurement of red blood cell and plasma volumes

OBJECTIVE

Our purpose was to demonstrate reduced blood volume in preeclampsia compared with nonproteinuric gestational hypertension and normal pregnancy by use of independent measures of red blood cell and plasma volumes.

STUDY DESIGN

Red blood cells labeled with a nonradioactive stable isotope of chromium and Evans' blue were infused in subjects with preeclampsia or gestational hypertension and normotensive pregnant controls. Blood was sampled eight times over 60 minutes for dye concentration and at 30 minutes for chromium analysis.

RESULTS

Total blood and plasma volumes are decreased in preeclampsia (2660 +/- 382 mL/m2 and 1790 +/- 332 mL/m2, respectively) compared with normotensive subjects (3217 +/- 391 mL/m2, P < 0.001 and 2279 +/- 325 mL/m2, P < .001) and gestational hypertension (3139 +/- 272 mL/m2, P < .001 and 2132 +/- 265 mL/m2, P = .003). Total body/peripheral hematocrit ratio is increased in preeclampsia.

CONCLUSIONS

Blood volume, by measurement of red blood cell and plasma volumes, is reduced and has altered distribution in preeclampsia but is normal in gestational hypertension.