Soluble interleukin-2 receptor (sIL-2r) level is a limited test for the diagnosis of adult secondary hemophagocytic lymphohistiocytosis

Background Soluble interleukin-2 receptor (sIL-2r) level is used as a diagnostic tool in hemophagocytic lymphohistiocytosis (HLH). However, evidence supporting its use among adults is inadequate. Objective and Methods We conducted a retrospective study to assess the performance characteristics of sIL-2r for the diagnosis of adult HLH. Results One hundred thirty-two adults with sIL-2r levels sent for evaluation of HLH over a ten-year period were included. Sixty-five (49%) met criteria for HLH. Mean sIL-2r was significantly higher among patients with HLH relative to all patients without HLH (12942U/ml vs. 6308 U/mL, P = .00311). However, when comparing mean sIL-2r in the HLH group to those in the non-HLH group with primary diagnoses of hematologic malignancy (8911 U/mL), sepsis (7127 U/mL), and rheumatologic disease (4624 U/mL), no significant differences were found (P = .241, P = .178, and P = .0607, respectively). There was only weak correlation between sIL-2r and diagnosis of HLH (r = .253). The standard cutoff sIL-2r > 2400 U/ml yielded a sensitivity of 89.2% and specificity of 38.8%. The area under the curve for the corresponding receiver-operator curve was 0.691, consistent with a poor discriminating ability for the diagnosis of HLH. Conclusions sIL-2r is a limited test for the diagnosis of adult secondary HLH, and its role in this setting should be reevaluated.