title: Comparison of three methods of diagnosis of plasma unmeasured anions in critically ill patients.
abstract: BACKGROUND
  The measurement of plasma unmeasured anions (PUA) is paramount in assessing metabolic acid base disorders. The aim of this study was to compare the accuracy of three methods in diagnosing abnormal PUA values: standard base excess (SBE), the albumin corrected anion gap (AGc), and the Stewart-Figge approach, based on unidentified anions (XAc-).
  
  
  METHODS
  Acid-base variables were prospectively collected in ICU patients admitted January-September 2008. Whatever the method, PUA values measured two standard deviations above or below the mean of those in control subjects were considered as abnormal.
  
  
  RESULTS
  Of the 205 consecutives patients included, 179 had an abnormal PUA value. The accuracy of AGc and XAc- in diagnosing abnormal PUA values was comparable (AUC: 0.89±0.03 and 0.89±0.03, P=0.82) but greater than that of SBE (0.67±0.06, P<0.001 and P<0.001, respectively). Of the high PUA values (n=161), 96% were diagnosed by XAc-, 88% by AGc (P<0.01) and 48% by SBE (P<0.001). Hyperlactatemia (n=111) was diagnosed equally by AGc and XAc-, (81% and 86%, P=0.37) but less by SBE (50%, P<0.001 and P<0.001, respectively). High PUA not associated with hyperlactatemia (N.=61) was more frequently diagnosed by XAc- (97%) than by AGc (84%, P=0.03).
  
  
  CONCLUSIONS
  In ICU patients, AGc and the Stewart-Figge approach should be preferred over SBE for diagnosing abnormal PUA values and predicting hyperlactatemia. The Stewart-Figge approach based on unidentified anions, is the most efficient in diagnosing high PUA values not associated with hyperlactatemia.
authors.affiliation: CHU Clermont-Ferrand, Service de Réanimation, Pôle REUNNIRH, Clermont-Ferrand, France - alautrette@chu-clermontferrand.fr.
authors.forename: A
authors.initials: A
authors.lastname: Lautrette
authors.forename: M
authors.initials: M
authors.lastname: Fejjal
authors.forename: A
authors.initials: A
authors.lastname: Aithssain
authors.forename: T N
authors.initials: TN
authors.lastname: Phan
authors.forename: N
authors.initials: N
authors.lastname: Caillot
authors.forename: A
authors.initials: A
authors.lastname: Fogli
authors.forename: B
authors.initials: B
authors.lastname: Souweine
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology; D000137:Acid-Base Imbalance / Q000097:blood / Q000628:therapy; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000838:Anions / Q000097:blood*; D001774:Blood Chemical Analysis; D002648:Child; D003422:Critical Care / Q000379:methods*; D016638:Critical Illness; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D010949:Plasma / Q000737:chemistry; D011446:Prospective Studies; D055815:Young Adult
chemical_list: D000838:Anions