Reduced Technetium 99m Labelled NCA-95/CEA-antibody Uptake in Liver Due to Gentle Antibody Reconstitution. Technical Note

The influence of reconstituting a murine monoclonal IgG1 antibody kit with pertechnetate technetium 99m on antibody distribution in the liver, spleen and sternal bone marrow of patients was examined. The 99mTc-labelled antibody used is directed against non-specific cross-reacting antigen (NCA-95) and carcinoembryonic antigen (CEA) and has been successfully applied for imaging tissue inflammation and bone marrow scanning. Radioactivity uptake was determined in the liver, spleen, bone marrow and a precordial background region in a consecutive series of 25 patients, examined with an antibody preparation, routinely radiolabelled according to the manufacturer's recommendations and in 14 patients, in whom the antibody was reconstituted with special care, avoiding bubble formation and dropping of buffer into the antibody-containing vial. Gentle compared with routine antibody reconstitution caused a highly significant reduction of the antibody uptake in the liver, as determined by count densities, normalized to injected dose and acquisition time (13.2 +/- 5.5 vs 20.1 +/- 6.0 cpm per pixel, means +/- SD, P = 0.008). The liver to background ratio was reduced from 3.4 +/- 1.4 to 1.9 +/- 0.5 (P less than 0.001). Spleen, sternal bone marrow and precordial background count rates were not significantly affected. These results clearly demonstrate that gentle antibody reconstitution can decrease non-specific antibody uptake in the liver by 34% +/- 6.4% (means +/- SEM). Thus, scan quality is improved, and the potential deleterious camouflage of underlying structures is avoided.