Reevaluating the role of ferritin in the diagnosis of adult secondary hemophagocytic lymphohistiocytosis

Background The standard diagnostic criteria for hemophagocytic lymphohistiocytosis (HLH) include hyperferritinemia to >500 ng/mL. This ferritin threshold is based on pediatric data, and evidence for its application among adults with secondary HLH is lacking. Objective and Methods We conducted a retrospective study assessing the relationship between extreme hyperferritinemia and adult secondary HLH at our institution. All adult inpatients seen over a 10-year period, with serum ferritin >5000 ng/mL, were included. Results Among 1055 patients with serum ferritin >5000 ng/mL, there were 69 cases of HLH (HLH prevalence of 6.5%). Mean ferritin among HLH patients was 70 398 ng/mL (SD 122 908), median 40 019 ng/mL (IQR 16 051-68 326). The prevalence of HLH only reached 50% as serum ferritin approached 90 000 ng/mL. A variety of conditions were contributory to hyperferritinemia, most commonly bacterial sepsis (33%), hematologic malignancy (29%), renal failure (24%), and liver injury (18%). The optimal cutoff ferritin for diagnosis of HLH was 16 000 ng/mL (sensitivity 79.4%, specificity 79.2%, PPV 20.9%, and NPV 98.2%). Conclusions The threshold ferritin levels used in diagnostic criteria for adult secondary HLH are too low to be clinically relevant, and efforts should be undertaken to revise them upward. Similar reappraisals should be taken of the other criteria used to diagnose adult HLH.