title: Serum and plasma neutrophil gelatinase associated lipocalin (NGAL) levels are not equivalent in patients admitted to intensive care.
abstract: BACKGROUND
  Neutrophil gelatinase associated lipocalin (NGAL) is proposed as a biomarker of acute kidney injury (AKI). NGAL has been studied in a range of body fluids including serum and EDTA plasma. The aim of the present study was to establish relationship between serum NGAL concentrations and EDTA plasma NGAL concentrations in patients admitted to intensive care units (ICUs) and whether these determinations are directly comparable in this setting.
  
  
  METHODS
  NGAL was measured in 40 paired samples of serum and EDTA plasma from 25 patients admitted to intensive care with a commercial particle-enhanced turbidimetric immunoassay (The NGAL Test™, BioPorto Diagnostics A/S, Gentofte, Denmark) on a Roche Hitachi 917 (Roche-Hitachi, Inc., Tokyo, Japan) analyzer.
  
  
  RESULTS
  Serum NGAL concentrations ranged from 26.8 to 1,808 ng/ml (median 281 ng/ml, interquartile range (IQR) 453 ng/ml). EDTA plasma NGAL concentrations ranged from 25.7 to 1,752 ng/ml (median 225 ng/ml, IQR 352 ng/ml). The difference in NGAL concentrations in paired serum and EDTA plasma samples (serum- plasma) ranged from -13.8 to 321 ng/ml (median 79 ng/ml, IQR 116 ng/ml; difference from zero, P < 0.0001, Wilcoxon's signed rank test). Although serum and EDTA plasma values were correlated (Spearman's r = 0.95, P < 0.0001), Deming regression analysis showed a slope of 1.1 that was not significantly different from unity (95% confidence interval (CI) 1.0-1.1) and a highly significant intercept of 67.9 ng/ml with a wide confidence interval (95% CI 29.8-106).
  
  
  CONCLUSIONS
  NGAL concentration values measured in serum and EDTA plasma cannot be directly compared and should not be used as equivalents in studies of patients admitted to intensive care.
authors.affiliation: Department of Anesthesiology, Nordsjaellands Hospital, Copenhagen University Hospital, Hillerød, Denmark.
authors.forename: Theis Skovsgaard
authors.initials: TS
authors.lastname: Itenov
authors.forename: Kristian
authors.initials: K
authors.lastname: Bangert
authors.forename: Per Hjort
authors.initials: PH
authors.lastname: Christensen
authors.forename: Jens-Ulrik
authors.initials: JU
authors.lastname: Jensen
authors.forename: Morten Heiberg
authors.initials: MH
authors.lastname: Bestle
mesh_terms: D000209:Acute-Phase Proteins; D003422:Critical Care; D004492:Edetic Acid; D006801:Humans; D000071068:Lipocalin-2; D054834:Lipocalins / Q000097:blood*; D011518:Proto-Oncogene Proteins / Q000097:blood*
chemical_list: D000209:Acute-Phase Proteins; C489506:LCN2 protein, human; D000071068:Lipocalin-2; D054834:Lipocalins; D011518:Proto-Oncogene Proteins; D004492:Edetic Acid
keywords: acute kidney injury; biomarkers; critical illness; neutrophil gelatinase-associated lipocalin (NGAL); plasma; serum