What is the optimum concentration of a red blood cell suspension used in blood bank testing?

• A. 1%-2%
• B. 2%-5%
• C. 5%-10%
• D. 10%-15%

Answer: (B)

In blood bank testing, the red blood cell suspension is prepared at a moderate concentration to optimize the visibility and reliability of antibody–cell reactions. If the suspension is too dilute, there aren’t enough cells for antibodies to bind, reducing sensitivity and risking missed reactions. If it’s too dense, cells can crowd and form rouleaux, leading to nonspecific agglutination that obscures true reactions or produces false positives. This balance provides consistent, interpretable results for common tests such as antibody screening and crossmatching, which is why a middle-ground concentration is used.