Measurement of circulating red cell volume using biotin-labeled red cells:validation against Cr-51-labeled red cells

BACKGROUND: Anemia is a serious problem in the fetus and preterm infant. To investigate the physiology and pathophysiology of anemia and to assess res ponses to blood transfusions or erythropoietin therapy, measurement of circ ulating red cell volume would be useful. Because the standard Cr-51 method exposes the subject to radiation, a method of measuring circulating red cel l volume without radiation exposure, sufficiently sensitive for use in fetu ses 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 Cr-51, mixed, and transfused intravenously. Circulating red cell v olume was measured in posttransfusion blood by quantitating the in vivo dil ution of biotinylated red cells. Biotinylated red cells were detected by tw o methods: 1) I-125-streptavidin and 2) fluorescein-labeled avidin with flo w cytometry. RESULTS: Circulating red cell volume measured by I-125-streptavidin detecti on agreed well with that measured by Cr-51 (slope = 1.07, y-intercept = -97 , correlation = 0.987). Similarly, circulating red cell volume measured by flow cytometry agreed well with that measured by Cr-51 (slope = 1.05, y-int ercept = -20, correlation = 0.987). CONCLUSIONS: Circulating red cell volume measured by the use of biotin with either I-125-streptavidin or flow cytometry agrees with that measured by C r-51. Each system provides a method of performing these studies without exp osing the subject to radiation.