The Human Neutrophil Lipocalin (HNL) also called NGAL, Lipocalin 2 etc. is produced by and secreted from epithelial cells and neutrophil granulocytes. In blood HNL exists in several molecular forms i.e. monomeric, dimeric and heteromeric forms. The latter form often in complex with MMP9. We purified dimeric HNL from human neutrophils and raised polyclonal and monoclonal against this native dimeric antigen. This procedure resulted in several unique antibodies which in combination uniquely detect the dimeric protein originating from neutrophils or the monomeric protein originating from epithelial cells. Several clinical studies were conducted and showed the immunoassays to be very useful diagnostic tools in the distinction between bacterial and viral infections, sepsis, sepsis with organ failure, sepsis monitoring, COVID-infections, acute kidney injury (AKI) and IBD/IBS. Depending on the disease in question and on the biological material obtained from the patient different formats of the HNL assays were used in order to optimize the clinical performance. In my presentation I will focus on the use of HNL immunoassays in infections and AKI.

Learning Objectives:

1. Discuss the fact that HNL exists in several different molecular forms with differences in cellular origins.

2. Explain how differences in antibody configurations of the HNL immunoassays identify different molecular forms of HNL and the impact on the clinical utilities of the assays.

3. Explain why depending on clinical question HNL is best measured after whole blood activation or in EDTA-plasma or in serum, which has been prepared in a standardized fashion, but also in urine and feces.

4. Conclude that the main clinical applications of HNL currently known are related to infections (bacterial-viral distinction and sepsis) and kidney injury, but more are to be discovered.