The OHI index performs better when assessed during routine surveillance and in treatment-naive patients. Kaplan-Meier curves of subgroup analyses of patients classified by using the OHI index. (A) Centers evaluating sCD25 and ferritin upon HLH suspicion only vs centers that have routine surveillance of patients with newly diagnosed lymphoma (Toyama Hospital in Japan and MD Anderson Cancer Center in the United States). (B) Treatment-naive patients vs pretreated patients. Although patients who received treatments that will undoubtedly influence their laboratory results (eg, cytoreductive therapy/high-dose steroids) were excluded from the study, patients who received minimal pretreatment (eg, lower dose steroids for only a few days) before assessment of relevant studies were included and defined in the pre-treatment group. The number at risk is presented for each group. Statistics were calculated with the log-rank (Mantel-Cox) test. *P < .05, **P < .01, ****P < .0001.