Human neutrophil lipocalin (HNL) as a biomarker of acute infections.

The early and accurate discrimination between bacterial and viral causes of acute infections is the key to a better use of antibiotics and will help slow down the fast-growing resistance to commonly used antibiotics. This discrimination is in the vast majority of cases possible to achieve by blood assay of the biomarker human neutrophil lipocalin (HNL), which we showed to be uniquely increased in patients suffering from bacterial infections. In serum, sensitivities and specificities of >90% are achieved in both adults and children. In order to eliminate the need to produce serum, a whole-blood assay with an assay time of <10 min was developed in which blood neutrophils are activated to release HNL. The diagnostic accuracy of this assay also showed sensitivities and specificities of >90% in most infectious diseases and was clearly superior to contemporary assays such as blood neutrophil counts, C-reactive protein, procalcitonin, and expression of CD64 on blood neutrophils. This format lends itself to the development of a point-of-care HNL assay and will be a major step forward to accomplish the goal of accurately diagnosing patients with symptoms of acute infections within 10 min at the emergency room or at the doctor's office.