In a WBC counting problem, a decrease in counts when using a different diluent is best explained by which mechanism?

In a WBC counting problem, a decrease in counts when using a different diluent is best explained by which mechanism?

• A. Lyse-resistant Hb C
• B. Lyse-sensitive Hb C
• C. Lyse-resistant target cells
• D. Lyse-sensitive target cells

Answer: (B)

The key idea is selective lysis of red cells by the diluent. Some WBC counting diluents are lysing, and red cells with Hb C are more fragile in certain solutions. When you switch to a diluent that is lyse‑sensitive for Hb C, many Hb C red cells are destroyed. This reduces the red cell population in the sample and can alter the particle milieu in the counting field, leading to an apparent decrease in the measured WBC count. In other words, the observed drop is best explained by the diluent causing lysis of Hb C–containing red cells, not by resistance to lysis or by lysis of other cell types.

The key idea is selective lysis of red cells by the diluent. Some WBC counting diluents are lysing, and red cells with Hb C are more fragile in certain solutions. When you switch to a diluent that is lyse‑sensitive for Hb C, many Hb C red cells are destroyed. This reduces the red cell population in the sample and can alter the particle milieu in the counting field, leading to an apparent decrease in the measured WBC count. In other words, the observed drop is best explained by the diluent causing lysis of Hb C–containing red cells, not by resistance to lysis or by lysis of other cell types.