Hyper‐interleukin (IL)‐6‐naemia in haemophagocytic lymphohistiocytosis

Clinical features in patients with haemophagocytic lymphohistiocytosis (HLH) have been demonstrated to be characterized by hypercytokinaemia. Previously, we reported the impact of high serum levels of interferon (IFN)-gamma and soluble IL-2 receptor (sIL-2R) on patient outcome; however, it was not known if serum levels of interleukin (IL)-6 also could be a prognostic factor. In a study during the active phase of disease in 25 cases of HLH in children and young adults (median age 3 years, range 0.1-23 years), we noted 12 cases which showed serum IL-6 > 100 (normal < 4.0) pg/ml. Five of these cases showed hyper-IL-6-naemia alone without hyper-IFN-gamma-naemia (group A) whereas seven cases showed both hyper-IL-6- and IFN-gamma-naemia (group B). Patient outcome did not differ between the patients with IL-6 > 100 pg/ml and those with IL-6 < 100 pg/ml, suggesting that high serum concentrations of IL-6 alone do not necessarily indicate poor prognosis in patients with HLH. Among the cases with hyper-IL-6-naemia ( > 100 pg/ml), underlying disorders causing haemophagocytosis were found to be different between groups A and B.