In labeling red blood cells with Cr51, what is the final step before re-injecting the labeled red blood cells into the patient?

The correct choice emphasizes the importance of using ascorbic acid after labeling red blood cells with chromium-51 (Cr51). During the labeling process, Cr51 is bound to the red blood cells, which can help in imaging and tracking blood flow and volume in the patient. However, excess unbound chromium can cause unwanted radiation exposure to the patient and lead to inaccurate results.

Adding ascorbic acid serves as a protective measure, reducing the potential for radiation effects from any free, unbound Cr51 that could not be incorporated into the red blood cells. This step is crucial in ensuring that only the properly labeled red blood cells are administered back to the patient, thus enhancing safety and the reliability of the diagnostic procedure. By doing this, the risk of potential toxicity or interference in imaging results is minimized.

The other options do not align with the critical final steps necessary for safe and effective re-injection. For instance, while washing labeled red cells to remove excess Cr51 might seem logical, it does not incorporate the specific protective aspect provided by ascorbic acid. Adding Cr51 directly to the patient’s blood sample wouldn’t be appropriate as it undermines the proper labeling protocol. Separating red blood cells from plasma is a standard laboratory practice but does not