On peripheral smear of a patient with hairy cell leukemia, which cytochemical stain is positive and not inhibited by tartrate?

• A Periodic acid-Schiff (PAS)
• B Sudan black B
• C Chloroacetate esterase
• D Tartrate-resistant acid phosphatase (TRAP) ✓

Explanation

Hairy cell leukemia cells express acid phosphatase isoenzyme 5 that is uniquely resistant to inhibition by L-(+)-tartrate, making TRAP positivity a classic diagnostic marker of this disease. PAS stains glycogen and is positive in ALL lymphoblasts and mucin-secreting cells. Sudan black B and chloroacetate esterase mark myeloid lineage cells. TRAP staining has largely been supplemented by flow cytometry (CD11c, CD25, CD103, CD123 expression), but the stain remains a classic NEET-tested point.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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