title: Ion-selective electrode and anion gap range: What should the anion gap be?
abstract: BACKGROUND
  Using flame photometry technique in the 1970s, the normal value of anion gap (AG) was determined to be 12 ± 4 meq/L. However, with introduction of the autoanalyzers using an ion-selective electrode (ISE), the anion gap value has fallen to lower levels.
  
  
  METHODS
  A retrospective study of US veterans from a single medical center was performed to determine the value of the anion gap in subjects with normal renal function and normal serum albumin and in patients with lactic acidosis and end-stage renal disease on dialysis.
  
  
  RESULTS
  In 409 patients with an estimated glomerular filtration rate ≥60 mL/min/1.73 m(2) body surface area and serum albumin ≥4 g/dL, the mean AG was 7.2 ± 2 (range 3-11) meq/L. In 299 patients with lactic acidosis (lactate level ≥4 meq/L) and 68 patients with endstage renal disease on dialysis, the mean AG was 12.5 meq/L and 12.4 meq/L, respectively. A value <2 meq/L should be considered a low anion gap and a possible clue to drug intoxication and paraproteinemic disorders.
  
  
  CONCLUSIONS
  With the advent of ISE for measurement of analytes, the value of the anion gap has fallen. Physicians need to be aware of the normal AG value in their respective institutions, and laboratories need to have an established value for AG based on the type of instrument they are using.
authors.affiliation: Jerry L Pettis Memorial Veterans Medical Center, Loma Linda University School of Medicine, Loma Linda, CA, USA.
authors.forename: Seyed-Ali
authors.initials: SA
authors.lastname: Sadjadi
authors.forename: Rendell
authors.initials: R
authors.lastname: Manalo
authors.forename: Navin
authors.initials: N
authors.lastname: Jaipaul
authors.forename: James
authors.initials: J
authors.lastname: McMillan
keywords: ESRD; acidosis; electrolytes