title: Day-to-day variation of urinary NGAL and rational for creatinine correction.
abstract: OBJECTIVE
  The number of clinical studies evaluating the new tubular biomarker urinary neutrophil gelatinase-associated lipocalin (U-NGAL) in urine are increasing. There is no consensus whether absolute U-NGAL concentrations or urinary NGAL/creatinine (U-NGAL/Cr) ratios should be used when chronic tubular dysfunction is studied. The aim was to study the biological variation of U-NGAL in healthy subjects and the rational for urinary creatinine (U-Cr) correction in two different study samples.
  
  
  METHODS
  To study biological variation of U-NGAL and U-NGAL/Cr ratio and the association between U-NGAL and U-Cr in healthy subjects 13 young males and females (median age 29 years) collected morning urine in 10 consecutive days. Additionally, a random subsample of 400 males from a population-based cohort (aged 78 years) collecting 24-hour urine during 1 day was studied.
  
  
  RESULTS
  The calculated biological variation for absolute U-NGAL was 27% and for U-NGAL/Cr ratio, 101%. Absolute U-NGAL increased linearly with U-Cr concentration (the theoretical basis for creatinine adjustment) in the older males (R=0.19, P<0.001) and with borderline significance in the young adults (R=0.16, P=0.08). The U-NGAL/Cr ratio was, however, negatively associated with creatinine in the older males (R=-0.14, P<0.01) and in the young adults (R=-0.16, P=0.07) indicating a slight "overadjustment."
  
  
  CONCLUSIONS
  The study provides some support for the use of U-NGAL/Cr ratio but the rather large biological variation and risk of possible overadjustment need to be considered. Both absolute U-NGAL and U-NGAL/Cr ratios should be reported for the estimation of chronic tubular dysfunction.
authors.affiliation: Department of Medical Sciences/Clinical Chemistry, Uppsala University, Uppsala University Hospital, SE-751 85 Uppsala, Sweden. Johanna.Helmersson_Karlqvist@medsci.uu.se
authors.forename: Johanna
authors.initials: J
authors.lastname: Helmersson-Karlqvist
authors.forename: Johan
authors.initials: J
authors.lastname: Arnlöv
authors.forename: Anders
authors.initials: A
authors.lastname: Larsson
mesh_terms: D000209:Acute-Phase Proteins / Q000652:urine*; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000652:urine; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000652:urine; D007684:Kidney Tubules / Q000502:physiology; D000071068:Lipocalin-2; D054834:Lipocalins / Q000652:urine*; D008297:Male; D011518:Proto-Oncogene Proteins / Q000652:urine*
chemical_list: D000209:Acute-Phase Proteins; D015415:Biomarkers; C489506:LCN2 protein, human; D000071068:Lipocalin-2; D054834:Lipocalins; D011518:Proto-Oncogene Proteins; D003404:Creatinine