Which stain is commonly positive in cases of hairy cell leukemia?

In the context of hairy cell leukemia, the acid phosphatase stain is notable because hairy cell leukemia cells typically exhibit a high level of activity for this enzyme. The significance of acid phosphatase staining lies in its ability to highlight the abnormal cells associated with this specific hematologic malignancy.

Hairy cell leukemia is characterized by the proliferation of small, atypically shaped lymphocytes with "hairy" projections that can be identified through various histological and cytological techniques. The positive reaction seen with acid phosphatase is essential for distinguishing hairy cell leukemia from other types of leukemia.

Other stains and techniques such as myeloperoxidase (MPO) stain, which detects myeloid cells, and leukocyte alkaline phosphatase, which assesses lymphocyte activity in other conditions, do not provide the same specificity for hairy cell leukemia. Giemsa stain, while useful in providing a general examination of the morphology of blood cells, also does not have the same diagnostic significance in this context. Therefore, the positive result for acid phosphatase is crucial in confirming a diagnosis of hairy cell leukemia.