Because it has no unique clinical, biologic, or histologic features, reactive hemophagocytic syndrome may be difficult to distinguish from other diseases such as severe sepsis or hematologic malignancies. This study was undertaken to develop and validate a diagnostic score for reactive hemophagocytic syndrome.

A multicenter retrospective cohort of 312 patients who were judged by experts to have reactive hemophagocytic syndrome (n = 162), were judged by experts to not have reactive hemophagocytic syndrome (n = 104), or in whom the diagnosis of reactive hemophagocytic syndrome was undetermined (n = 46) was used to construct and validate the reactive hemophagocytic syndrome diagnostic score, called the HScore. Ten explanatory variables were evaluated for their association with the diagnosis of hemophagocytic syndrome, and logistic regression was used to calculate the weight of each criterion included in the score. Performance of the score was assessed using developmental and validation data sets.

Nine variables (3 clinical [i.e., known underlying immunosuppression, high temperature, organomegaly], 5 biologic [i.e., triglyceride, ferritin, serum glutamic oxaloacetic transaminase, and fibrinogen levels, cytopenia], and 1 cytologic [i.e., hemophagocytosis features on bone marrow aspirate]) were retained in the HScore. The possible number of points assigned to each variable ranged from 0–18 for known underlying immunosuppression to 0–64 for triglyceride level. The median HScore was 230 (interquartile range [IQR] 203–257) for patients with a positive diagnosis of reactive hemophagocytic syndrome and 125 (IQR 91–150) for patients with a negative diagnosis. The probability of having hemophagocytic syndrome ranged from <1% with an HScore of ≤90 to >99% with an HScore of ≥250.

The HScore can be used to estimate an individual's risk of having reactive hemophagocytic syndrome. This scoring system is freely available online (http://saintantoine.aphp.fr/score/).