Apparent rejuvenation of transfused donor blood in the fetus is due to accelerated removal of the older RBCs.

Abstract

In severely anemic fetuses of women alloimmunized to RBC antigens, transfused donor RBCs disappear faster than in adults. This may result from an accelerated linear or nonlinear decline with time. It was investigated whether changes in donor RBC age characteristics after circulation in the fetus may reflect the main type of cellular decline. Donor RBC age characteristics (density, mean cell volume [MCV], and mean cell Hb content [MCHC]) were determined before intrauterine transfusions. Density gradient centrifugation was used to obtain RBCs of different ages. The results from gradient centrifugation were used to calculate mean values for the density, MCV, and MCHC to be expected after the transfusion interval, assuming a linear decline in RBCs of 1 percent per day. Donor and fetal RBCs, taken just before the second transfusion, were separated by agglutination with IgM D MoAb. For these donor cells, the observed mean values for density, MCV, and MCHC were compared with the calculated, expected values (n = 12). The mean +/- SD transfusion interval was 17.9 +/- 3.6 days. The Hb declined by 1.75 +/- 0.62 percent per day (n = 9). After the transfusion interval and contrary to the expected changes, cell density and MCHC decreased and MCV increased significantly (0. 001<p<0.02). This difference between actual and calculated values decreased with increasing intervals; for MCV, it was also associated with a greater decline in Hb per day (p<0.05). All donor cells age during circulation in the fetus. However, after the transfusion interval, the donor RBC population remaining is apparently younger than the RBC population before transfusion. This results from a preferential disappearance of older donor RBCs and not from a linear loss of cells with time. The removal of older RBCs before the transfusion may increase the time between transfusions and thereby reduce the total number of transfusions required.