EVALUATION OF CIRCULATING BLOOD VOLUME USING IN VIVO LABELING OF RED BLOOD CELLS WITH TECHNETIUM-99m

In vivo labeling of red blood cells with technetium-99m (Tc-99m) has recently been recommended for blood pool imaging. We have attempted to measure circulating blood volume (CBV) by counting the activity of drawn peripheral blood while performing blood pool imaging. In order to obtain a useful method of quantitative evaluation in an in vivo study, stability of technetiurn-99m-labeled red blood cells (Tc-99m RBO in necessary. The same results were obtained in our laboratory as in previous studies already described. It was proved that red blood cell labeling efficiency was 94.8% (± 0.8%, S.D.) 15-60 minutes after intravenous injection of pertechnetate, and that Tc-99m RBC remained stable during these 60 minutes, during which time CBV for in vivo studies is available. CBVS were also simultaneously measured by methods such as the chromium-51-labeled red blood cell (Cr-51 RBC method and nomogram. A correlation coefficient of 0.900 was obtained for the CBV of the Cr-51 RBC method (4.1% overestimate) and 0.768 for the nomogram. In vitro studies (including the Cr-51 RBC method) require not only sterile but also complicated techniques. In contrast, in vivo studies can be performed more easily and rapidly in comparison with such methods. In conclusion, in vivo study with Tc-99m is recommended for evaluation of circulating blood volume in nuclear medicine.