Increased urinary neutrophil gelatinase associated lipocalin in urinary tract infections and leukocyturia

Background: Neutrophil gelatinase associated lipocalin (NGAL) is a protein present in neutrophils. NGAL is a promising biomarker for acute kidney injury. In urinary tract infections, urinary neutrophils can be a potential source of urinary NGAL. We investigated the effects of urinary tract infection and urinary neutrophil counts on urinary NGAL values. Methods: NGAL was assayed using an immunoassay (ARCHITECT). Urine flowcytometry was performed with the UF-1000i (Sysmex). Results: A correlation between the urinary white blood cell (WBC) count and NGAL concentrations was observed: log(Y) (NGAL, mu g/L) = 1.284 + 0.439 log(X) (urinary WBC, 10(9) cells/L); r = 0.518. Similarly, the bacterial count correlated weakly with NGAL: log(Y) (NGAL, mu g/L) = 1.796 + 0.124 log(X) (bacterial count, 10(9) cells/L); r = 0.243. Albuminuria correlated moderately with NGAL values: log(Y) (NGAL, mu g/L) = 1.557 + 0.339 log(X) (albuminuria, mg/L); r = 0.368; alpha(1)-microglobulin (a1M) correlated weakly with NGAL: log(Y) (NGAL, mu g/L) = 1.631 + 0.360 log(X) (a1M, mg/L); r = 0.381. Conclusions: Leukocyte contributions to urinary NGAL concentrations can be important. In leukocyturia or tubular damage (e. g., intensive care patients), using a fixed cut-off value for interpreting urinary NGAL data can lead to false positive results. Therefore, we suggest a mathematical correction in cases with pyuria (> 100 x 1(0)9 cells/L) and urinary NGAL concentration > 100 mu g/L: corrected NGAL (mu g/L) = NGAL-0.12 (urinary WBC, 10(9) cells/L).