title: The comparison of the commonly used surrogates for baseline renal function in acute kidney injury diagnosis and staging.
abstract: BACKGROUND
  Baseline serum creatinine (SCr) level is frequently not measured in clinical practice. The aim of this study was to investigate the effect of various methods of baseline SCr determination measurement on accuracy of acute kidney injury (AKI) diagnosis in critically ill patients.
  
  
  METHODS
  This was a retrospective cohort study. All adult intensive care unit (ICU) patients admitted at a tertiary referral hospital from January 1, 2011 through December 31, 2011, with at least one measured SCr value during ICU stay, were included in this study. The baseline SCr was considered either an admission SCr (SCrADM) or an estimated SCr, using MDRD formula, based on an assumed glomerular filtration rate (GFR) of 75 ml/min/1.73 m(2) (SCrGFR-75). Determination of AKI was based on the KDIGO SCr criterion. Propensity score to predict the likelihood of missing SCr was used to generate a simulated cohort of 3566 patients with baseline outpatient SCr, who had similar characteristics with patients whose outpatient SCr was not available.
  
  
  RESULTS
  Of 7772 patients, 3504 (45.1 %) did not have baseline outpatient SCr. Among patients without baseline outpatient SCr, AKI was detected in 571 (16.3 %) using the SCrADM and 997 (28.4 %) using SCrGFR-75 (p < .001). Compared with non-AKI patients, patients who met AKI only by SCrADM, but not SCrGFR-75, were significantly associated with 60-day mortality (OR 2.90; 95 % CI 1.66-4.87), whereas patients who met AKI only by SCrGFR-75, but not SCrADM, had a non-significant increase in 60-day mortality risk (OR 1.33; 95 % CI 0.94-1.88). In a simulated cohort of patients with baseline outpatient SCr, SCrGFR-75 yielded a higher sensitivity (77.2 vs. 50.5 %) and lower specificity (87.8 vs. 94.8 %) for the AKI diagnosis in comparison with SCrADM.
  
  
  CONCLUSIONS
  When baseline outpatient SCr was not available, using SCrGFR-75 as surrogate for baseline SCr was found to be more sensitive but less specific for AKI diagnosis compared with using SCrADM. This resulted in higher incidence of AKI with larger likelihood of false-positive cases.
authors.affiliation: Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA. charat.thongprayoon@gmail.com.
authors.forename: Charat
authors.initials: C
authors.lastname: Thongprayoon
authors.affiliation: Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.
authors.forename: Wisit
authors.initials: W
authors.lastname: Cheungpasitporn
authors.affiliation: Medical Scientist Training Program, Mayo Clinic, Rochester, MN, USA.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Harrison
authors.affiliation: Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.
authors.forename: Wonngarm
authors.initials: W
authors.lastname: Kittanamongkolchai
authors.affiliation: Division of Rheumatology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Patompong
authors.initials: P
authors.lastname: Ungprasert
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Mayo Clinic, Rochester, MN, USA.
authors.forename: Narat
authors.initials: N
authors.lastname: Srivali
authors.affiliation: Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.
authors.forename: Abbasali
authors.initials: A
authors.lastname: Akhoundi
authors.affiliation: Division of Nephrology and Hypertension, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.|Division of Pulmonary and Critical Care Medicine, Mayo Clinic, Rochester, MN, USA.
authors.forename: Kianoush B
authors.initials: KB
authors.lastname: Kashani
mesh_terms: D058186:Acute Kidney Injury / Q000097:blood* / Q000175:diagnosis* / Q000401:mortality; D000368:Aged; D000369:Aged, 80 and over; D000553:Ambulatory Care; D015415:Biomarkers / Q000097:blood; D003404:Creatinine / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D055641:Mathematical Concepts; D008875:Middle Aged; D010343:Patient Admission; D057216:Propensity Score; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
chemical_list: D015415:Biomarkers; D003404:Creatinine