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Tc-99m-Labeled Red Blood Cells for the Measurement of Red Cell Mass in Newborn Infants: Concise Communication

University of Munich, Munich, Federal Republic of Germany

Correspondence: For reprints contact: O. Linderkamp, MD, Dept. of Pediatrics, Lindwurmstr. 4, D-8000 München 2, Federal Republic of Germany.

ABSTRACT

In vitro and in vivo investigations were performed to examine the binding of Tc-99m to neonatal red blood cells (RBC). Labeling efficiency was about 90%, and unbound Tc-99m less than 3% after one washing,in premature and full-term new-borns and in children. Thus presence of high percentages of fetal hemoglobin (Hb F) did not influence the labeling of RBCs with Tc-99m. RBCs of 11 newborns were hemolysed and the distribution of Tc-99m on RBC components was analyzed. Although Hb F percentage averaged (60.0 ± 8.1)% (s.d.), only (11.9 ± 3.7)% of Tc-99m was bound by Hb F, whereas (45.0 ± 6.1)% was associated with Hb A. RBC membranes bound (13.7 ± 4.3)% and (29.3 ± 4.0)% were found unbound in hemolysates.These results indicate that Tc-99m preferentially binds to beta chains. In vivo equilibration of Tc-99m RBCs and of albumin labeled with Evans blue was investigated in five newborn infants. Tc-99m RBCs were stable in each case during the first hour after injection. Elution of Tc-99m from RBCs was (3.4 ± 1.5)% per hour. Body-to-venous hematocrit ratio averaged 0.86 ± 0.03.