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NGAL levels are dramatically increased in urine and plasma from patients with acute kidney injury (AKI). In this study we tested the clinical utility of NGAL in critically ill patients with many confounding conditions including sepsis. In addition, a new fully automated NGAL assay was validated with a selection of clinical samples from these patients.
Plasma and urinary NGAL was monitored (daily to alternate days) in 135 consecutive patients admitted to intensive care. AKI was classified according to the RIFLE criteria. Three patients were excluded because of incomplete data. NGAL was determined with an ELISA kit (BioPorto Diagnostics). Differences between maximal NGAL levels in the patient were analyzed nonparametrically by the Kruskal-Wallis test. Data are reported as median (interquartile range) in ng/ml. A fully automated immunoturbidimetric NGAL test (The NGAL Test; BioPorto Diagnostics) was tested. The NGAL Test was validated by means of linearity studies with dilutions of calibrator material, determination of antigen excess zone and a method comparison with the ELISA kit on 40 urine and 40 plasma samples with NGAL levels from 25 to 2,995 ng/ml as measured by ELISA.
Sixty-two patients did not have AKI; 15 were classified as risk (R), 11 as injury (I) and 44 as failure (F). The urinary NGAL was significantly (P < 0.0001) higher in patients with AKI (R 377 (102 to 830), I 519 (321 to 1,845) and F 2,747 (559 to 7,621)) than in patients without AKI (51 (29 to 213)). Plasma NGAL levels were significantly (P < 0.0001) higher in patients with AKI (R 354 (259 to 511), I 546 (331 to 1,106) and F 1,062 (584 to 1,817)) than in patients without AKI (199 (128 to 308)). Linearity studies of The NGAL Test demonstrated a measuring range from 25 to 5,000 ng/ml. No deleterious effect of antigen excess was seen up to a level of 40,000 ng/ml. There was good agreement between the ELISA and The NGAL Test results, the Pearson coefficient of correlation being 0.98 for both urine and plasma samples.
It is concluded that NGAL is dramatically increased in the urine and plasma of unselected critically ill patients with AKI and the degree of injury is reflected by the observed levels despite several confounding conditions. NGAL determination may therefore be useful for the diagnosis of renal injury and monitoring the management of patients admitted to intensive care. Validation of The NGAL Test demonstrates a performance that complies with the expectations for a fully automated clinical laboratory assay, which can thus be a valuable tool for the management of critically ill patients.