Which of the following statements concerning the washing of cells is true?

• A. Washing should be done after AHG reagent addition
• B. Red blood cells must be washed quickly to avoid antibody neutralization
• C. Washing is optional
• D. Red blood cells should be washed with distilled water

Answer: (B)

Washing red cells serves to remove unbound antibodies and plasma proteins that could interfere with the test by causing non-specific reactions or masking the antibody actually bound to the cells. This step is essential for the antiglobulin reagent (AHG) to detect only those antibodies that are truly attached to the red cells, not free antibodies in solution. The wash should be done with isotonic saline in multiple cycles after incubation and before adding AHG; washing after AHG would remove the reagent itself and ruin the result. Distilled water must not be used because its hypotonic nature would lyse the cells. Although the term “neutralization” isn’t the exact technical description, the idea behind washing promptly is to prevent free antibodies from interfering with the detection of cell-bound antibodies.