α-Hemoglobin-stabilizing protein is a sensitive and specific marker of erythroid precursors.

α-Hemoglobin-stabilizing protein (AHSP) is an abundant erythroid-specific chaperone protein that facilitates incorporation of nascent α-globin into hemoglobin A. We characterized AHSP expression by immunohistochemistry in a panel of 100 neoplastic and reactive bone marrow biopsies and splenic tissue with extramedullary hematopoiesis and compared it with established erythroid markers CD71 and CD235a. In all cases, AHSP expression was limited to physiological nucleated erythroid precursors (EPs) and blasts in erythroid leukemias. Although CD71 also stained EPs, it additionally stained nonerythroid malignant cells to varying extents in acute leukemia, diffuse large B-cell lymphoma, metastatic carcinomas, and small round blue cell tumors. In contrast, CD235a staining was erythroid-specific but stained non-nucleated red blood cells in all specimens, limiting its utility. We conclude that AHSP is superior to CD71 and CD235a for detecting normal and neoplastic nucleated EPs.