A myeloperoxidase stain is performed on peripheral blood cells of a patient with acute leukemia and 85% blasts; the patient has an occasional mature neutrophil

When the stained slide is evaluated, the blasts are all negative but the mature neutrophils are strongly positive. What is the significance of this finding?

a. The stain worked (internal positive control).
b. Nothing can be determined until a positive control is also examined.
c. Nothing can be determined because mature neutrophils are always positive.
d. Nothing can be determined because only examination of the blasts is useful.

ANS: A
The finding of positive neutrophils on the slide serves as an internal quality control to validate that the stain worked. If only blasts had been present (no mature neutrophils), and they were all negative, it would be crucial to examine the positive control stained at the same time before a negative result in the blasts would be significant. Proof that the staining was successful must exist before any result on blasts has meaning.