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P144. Urinary NGAL: A reliable marker of minor tubular injury in inflammatory bowel disease

K. Oikonomou1, F. Tsiopoulos1, K. Andritsopoulos1, I. Apostolopoulos2, N. Magaliou1, A. Manolakis3, I. Tsiompanidis1, A. Kapsoritakis1, S. Potamianos4

1University of Thessaly, Larissa, Greece; 2University of Thessaly, Greece; 3University of Thessaly, Gastroenterology, Larissa, Greece; 4University of Thessaly, Department of Gastroenterology, Larissa, Greece

Background: Diverse observations regarding the impact of either disease activity or aminosalicylates on tubular function of patients with inflammatory bowel disease (IBD) have been reported. Aim of this study was to evaluate tubular damage in IBD patients based on a novel marker, neutrophil gelatinase-associated lipocalin (NGAL), and to correlate it with multiple factors of renal function and bowel inflammation.

Methods: NGAL and alpha-1-microglobulin (a1-MG) were determined by sandwich enzyme-linked immunosorbent assay (ELISA) in urine samples of 181 IBD patients, 93 with ulcerative colitis (UC) and 88 with Crohn's disease (CD), and 82 healthy controls (HC).

Results: Urinary NGAL levels were 5.45 (0.6–77.5) ng/mL in IBD patients, 5.25 (1.2–74.5) ng/mL in UC and 5.9 (0.6–77.5) ng/mL in CD, being marginally increased compared to HC, 5.1 (0.4–28) ng/mL. However, no statistically significant difference among patients and controls was established (overall p = 0.577 and p > 0.05 between subgroups in post-hoc analysis). No significant correlation of urinary NGAL with characteristics of patients and disease were observed. Administration of aminosalicylates in particular, did not impact urinary NGAL in both UC and CD (p = 0.653 and p = 0.791, respectively). Disease activity did not affect NGAL in UC (p = 0.620), whereas a trend observed in CD (p = 0.051) was eliminated after adjustment for all potential covariates. Furthermore, renal function, based on serum creatinine and serum cystatin C, was not correlated with urinary NGAL concentrations (Spearman r = −0.023, p = 0.882 and Spearman r = 0.173, p = 0.266, respectively). Urinary NGAL levels were strongly correlated with urinary a1-MG in both UC and CD patients as well as in HC subgroups (p = 0.003, p = 0.009. and p = 0.002, respectively). Additionally, occurrence of tubular injury based on urinary a1-MG concentrations was similar in UC and CD patients as well as in IBD patients compared to HC; UC/CD p = 0.307, UC/HC p = 0.925, CD/HC p = 0.510 and IBD/HC p = 0.766.

Conclusions: Urinary NGAL is an independent and reliable marker of tubular injury, strongly correlating with urinary a1-MG. Occurrence of tubular injury in IBD patients appears to be equal to that of healthy subjects, showing no dependency on either degree of inflammation or medical treatment.