In a red cell volume determination, why is ascorbic acid added to the labeled red cells?

Ascorbic acid is added to labeled red cells primarily to prevent additional tagging once the cells are re-injected into the patient. When red cells are labeled with a radioactive tracer, such as chromium-51 (51Cr), it is important to ensure that the radioactivity remains associated with the labeled red blood cells and does not bind to other cells or proteins in the patient’s bloodstream upon reinfusion. By adding ascorbic acid, it helps to stabilize the labeled red cells and minimize the chance of the label being reattached to any new cells or proteins, thus ensuring accurate measurement and assessment of the red cell volume.

Adding ascorbic acid does not serve to remove unbound 51Cr from the sample, prevent coagulation, or directly assess the anemic status of the patient. Rather, its primary role is focused on maintaining the integrity of the labeled cells during the reinfusion process, thus allowing for more precise monitoring and evaluation of red cell volume post-injection.