Increased human neutrophil lipocalin and its clinical relevance in adult-onset Still's disease

BACKGROUND: Human neutrophil lipocalin (HNL) has been used extensively to differentiate acute bacterial infection from febrile diseases as a biomarker to reflect the activation of the neutrophil. The serum HNL levels in the adult-onset Still's disease (AOSD) patients with and without infection, as well as the healthy controls (HCs), were analyzed statistically in this study to evaluate the value of HNL for the diagnosis of AOSD. METHODS: A total of 129 AOSD patients were enrolled, from whom blood samples were drawn and the AOSD diagnosis was confirmed through the review of the medical records, where the systemic score, demographic characteristics, clinical manifestations, and laboratory parameters were also collected for the patients; in addition, a total of 40 HCs were recruited among the blood donors from the healthcare center with the relevant information collected. The HNL test was done for the blood samples with the enzyme-linked immunosorbent assay and the analyses were done for the correlations of HNL with clinical manifestations and diagnostic effectiveness. RESULTS: The serum HNL increased significantly in the patients with only AOSD as compared with that in the HCs (139.76 ± 8.99 ng/mL vs. 55.92 ± 6.12 ng/mL; P < 0.001). The serum HNL level was correlated with the white blood cell (WBC) count (r = 0.335, P < 0.001), neutrophil count (r = 0.334, P < 0.001), erythrocyte sedimentation rate (r = 0.241, P = 0.022), C-reactive protein (r = 0.442, P < 0.0001), and systemic score (r = 0.343, P < 0.0001) in the AOSD patients significantly. Patients with fever, leukocytosis ≥15,000/mm(3), and myalgia in the HNL-positive group were observed relatively more than those in the HNL-negative group (P = 0.009, P = 0.023, and P = 0.007, respectively). HNL was a more sensitive indicator than ferritin and C-reactive protein (CRP) to differentiate the AOSD patients with bacterial infection from AOSD-only patients, and the Youden index was 0.6 for HNL and 0.29 for CRP. CONCLUSION: Serum HNL can be used as a biomarker for the diagnosis of the AOSD, and HNL is also observed to be associated with the disease activity.