title: Correcting the anion gap for hypoalbuminaemia does not improve detection of hyperlactataemia.
abstract: BACKGROUND
  An elevated lactate level reflects impaired tissue oxygenation and is a predictor of mortality. Studies have shown that the anion gap is inadequate as a screen for hyperlactataemia, particularly in critically ill and trauma patients. A proposed explanation for the anion gap's poor sensitivity and specificity in detecting hyperlactataemia is that the serum albumin is frequently low. This study therefore, sought to compare the predictive values of the anion gap and the anion gap corrected for albumin (cAG) as an indicator of hyperlactataemia as defined by a lactate > or =2.5 mmol/l.
  
  
  METHODS
  A retrospective review of 639 sets of laboratory values from a tertiary care hospital. Patients' laboratory results were included in the study if serum chemistries and lactate were drawn consecutively. The sensitivity, specificity, and predictive values were obtained. A receiver operator characteristics curve (ROC) was drawn and the area under the curve (AUC) was calculated.
  
  
  RESULTS
  An anion gap > or =12 provided a sensitivity, specificity, positive predictive value, and negative predictive value of 39%, 89%, 79%, and 58%, respectively, and a cAG > or =12 provided a sensitivity, specificity, positive predictive value, and negative predictive value of 75%, 59%, 66%, and 69%, respectively. The ROC curves between anion gap and cAG as a predictor of hyperlactataemia were almost identical. The AUC was 0.757 and 0.750, respectively.
  
  
  CONCLUSIONS
  The sensitivities, specificities, and predictive values of the anion gap and cAG were inadequate in predicting the presence of hyperlactataemia. The cAG provides no additional advantage over the anion gap in the detection of hyperlactataemia.
authors.affiliation: Department of Internal Medicine, University of Hawaii, John A Burns School of Medicine, Honolulu, HI 96816, USA.
authors.forename: C H
authors.initials: CH
authors.lastname: Dinh
authors.forename: R
authors.initials: R
authors.lastname: Ng
authors.forename: A
authors.initials: A
authors.lastname: Grandinetti
authors.forename: A
authors.initials: A
authors.lastname: Joffe
authors.forename: D C
authors.initials: DC
authors.lastname: Chow
mesh_terms: D000136:Acid-Base Equilibrium; D000137:Acid-Base Imbalance / Q000628:therapy*; D019540:Area Under Curve; D016638:Critical Illness; D006801:Humans; D034141:Hypoalbuminemia / Q000097:blood*; D007773:Lactates / Q000097:blood*; D011237:Predictive Value of Tests; D012016:Reference Values; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012709:Serum Albumin / Q000032:analysis*
chemical_list: D007773:Lactates; D012709:Serum Albumin