Is neutrophil gelatinase-associated lipocalin an optimal marker of renal function and injury in liver transplant recipients?

BACKGROUND: Recently, research has focused on the association of neutrophil gelatinase-associated lipocalin (NGAL) with acute and/or active kidney injury. However, it should be remembered that NGAL is involved in iron metabolism and antimicrobial defense mechanisms.

METHODS: One hundred seven consecutive liver transplant recipients were included in this study. Plasma and urine NGAL levels were measured with the use of enzyme-linked immunosorbent assay. NGAL levels were studied as plasma concentrations (pNGAL), urine concentrations (uNGAL), urinary NGAL to creatinine ratio (uNGAL/Cr), and fractional NGAL secretion (fNGAL).

RESULTS: pNGAL was found to be inversely correlated with estimated glomerular filtration rate (eGFR) and plasma cystatine C (pCysC) (r = -0.26 and P = .007, r = -0.38 and P = .00006, respectively). uNGAL was positively correlated with urinary cystatine C to creatinine ratio (uCysC/Cr) and fractional cystatine C excretion (fCysC) (r = 0.43 and P = .000004; r = 0.4 and P = .1; respectively). uNGAL/Cr was inversely correlated with hematocrit (Htc) and hemoglobin (Hb) (r = -0.35 and P = .0002; r = -0.39 and P = .00004; respectively), and positively correlated with uCysC/Cr (r = 0.5 and P < .0000001). fNGAL was directly correlated with uCysC/Cr and fCysC (r = 0.53 and P < .0000001; r = 0.39 and P = .00005; respectively) and inversely correlated with red blood cell count (RBC; r = -0.31 and P = .001). We observed significant differences of pNGAL, uNGAL/Cr, and fNGAL between sexes, with highest values of uNGAL, uNGAL/Cr, and fNGAL in women and pNGAL in men. In multivariate regression analysis, pNGAL was positively correlated with time elapsed from liver transplantation, neutrophil count, pCysC, and sex (β = 0.36 and P = .00001; β = 0.32 and P = .0001; β = 0.58 and P < .0000001; β = 0.17 and P = .025; respectively) and inversely correlated with patient's age (β = -0.18 and P = .02) with R = 0.67 and R(2) = 0.45, independently from blood glucose, eGFR, RBC, white blood cell count, Hb, uCysC, uCysC/Cr, and fCysC.

CONCLUSIONS: Plasma and urine NGAL levels are strongly correlated not only with kidney function parameters, but also with red and white blood cell parameters and patient's age and sex.