The identification of hemophagocytosis (HPC) in tissue or bone marrow (BM) represents only one of 5/8 criteria needed for the diagnosis of hemophagocytic lymphohistiocytosis (HLH). Yet, confirmation of HPC in bone marrow aspirates (BMA) is often relied upon to make therapeutic decisions. There is no standardized reporting criteria for the definition of “positive” BMA, and likely differs between institutions. The purpose of this study was to quantify the number of HPC in the initial BMA in patients diagnosed with HLH at our institution.

Patient charts were retrospectively reviewed. Numbers of HPC were counted per 500 nucleated cells in initial BMA.

Fifty‐eight percent of patients had at least one HPC per 500 nucleated cells. Median number of HPC per 500 cells was 1 (0–12). Median time from initial BMA to HLH diagnosis was 0 days (−3 to 11), suggesting that HLH diagnosis was made regardless of the results of this initial BMA.

The number of HPC at initial BMA is often low and variable, confirming that a BMA lacking HPC does not rule out the diagnosis of HLH, and a negative initial BMA should not delay therapy. We recommend that the BMA report should document negative as well as any positive findings of HPC. Pediatr Blood Cancer 2008;51:402–404. © 2008 Wiley‐Liss, Inc.