Neutrophil gelatinase-associated lipocalin (NGAL): validation of commercially available ELISA.

BACKGROUND: Neutrophil Gelatinase-Associated Lipocalin (NGAL) has been described as an excellent marker of acute kidney injury (AKI) using the enzyme-linked immunosorbent assay (ELISA) from BioPorto Diagnostics, DK. Validation of the ELISA kit and investigation of stability of the NGAL protein is a prerequisite before introducing NGAL as a marker for AKI in clinical research.
METHODS: Plasma and urine samples from a healthy adult and from 16 children undergoing surgery for congenital heart disease were used to validate the 036 NGAL ELISA kit from BioPorto Diagnostics and study stability of the NGAL protein.
RESULTS: Median intra-assay variation in plasma and urine from the healthy adult was <5% and median inter-assay variation was <10%. For children undergoing surgery for congenital heart disease intra-assay variation was <10%. ELISA kit batch-to-batch variation for plasma was 14.6%. We observed excellent results on analysis of linearity and spike-recovery and found no clinically important variation of NGAL measurements throughout the ELISA plate. Haemolysis significantly interfered with measurement of NGAL, whereas repeated thawing or 48 h of 4-5 degrees C-storage before centrifugation and storage at -80 degrees C did not influence NGAL measurements (ANOVA; n.s.). The NGAL protein is stable in plasma for at least 11 months at -80 degrees C.
CONCLUSION: 036 NGAL ELISA kit from BioPorto Diagnostics can be used with acceptable precision for plasma and urine. However, the presence of haemolysis in blood samples or the use of different batches of ELISA kits may seriously decrease the accuracy of measurements.