Measurement of circulating red cell volume using biotin‐labeled red cells: validation against51Cr‐labeled red cells

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Abstract
BACKGROUND: Anemia is a serious problem in the fetus and preterm infant. To investigate the physiology and pathophysiology of anemia and to assess responses to blood transfusions or erythropoietin therapy, measurement of circulating red cell volume would be useful. Because the standard 51Cr method exposes the subject to radiation, a method of measuring circulating red cell volume without radiation exposure, sufficiently sensitive for use in fetuses and infants, was developed. STUDY DESIGN AND METHODS: In 10 healthy adults whose body mass ranged from 56.8 to 115.9 kg, aliquots of autologous red cells were labeled with biotin or with 51Cr, mixed, and transfused intravenously. Circulating red cell volume was measured in posttransfusion blood by quantitating the in vivo dilution of biotinylated red cells. Biotinylated red cells were detected by two methods: 1) 125I‐streptavidin and 2) fluorescein‐labeled avidin with flow cytometry. RESULTS: Circulating red cell volume measured by 125I‐ streptavidin detection agreed well with that measured by 51Cr (slope = 1.07, y‐intercept = −97, correlation = 0.987). Similarly, circulating red cell volume measured by flow cytometry agreed well with that measured by 51Cr (slope = 1.05, y‐intercept = −20, correlation = 0.987). CONCLUSIONS: Circulating red cell volume measured by the use of biotin with either 125I‐streptavidin or flow cytometry agrees with that measured by 51Cr. Each system provides a method of performing these studies without exposing the subject to radiation.