Leukemoid Reactions — Not Always Caused by Infection

Markedly elevated peripheral white blood cell counts with neutrophilia have been termed leukemoid reactions. Although definitions differ, most involve a white blood cell count ≥25,000 × 10⁹/µL with a predominance of granulocytes, a shift toward more-immature forms such as band neutrophils and metamyelocytes, and the absence of dysplastic changes. Although infection is presumed to account for most instances of leukemoid reaction, other conditions may be causative.

Few data are available on the etiology of leukemoid reactions among large, heterogeneous populations. To remedy this situation, researchers in Israel searched hospital laboratory records for adults who were admitted to a medical center in Haifa between March 2011 and February 2012 a…