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.
We conducted a retrospective study to assess the performance characteristics of sIL-2r for the diagnosis of adult HLH.
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. 6308U/ml, p=0.00311). However, when comparing mean sIL-2r in the HLH group to those in the non-HLH group with primary diagnoses of hematologic malignancy (8911U/ml), sepsis (7127U/ml), and rheumatologic disease (4624U/ml), no significant differences were found (p=0.241, p=0.178, and p=0.0607 respectively). There was only weak correlation between sIL-2r and diagnosis of HLH (r=0.253). The standard cutoff sIL-2r > 2,400 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.
sIL-2r is a limited test for the diagnosis of adult secondary HLH and its role in this setting should be reevaluated.

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