Tuesday, July 9, 2013

Topic Discussion: Anion Gap

What are the limitations of the anion gap use? A recent article in CJASN has some key points.

A.Uses of anion gap
1. evaluate met acidosis
2. detect paraproteins
B. Classically AG has been using HCO3, Cl and Na for calculations. Should K be used? The rationale for not using K is because the absolute change in its concentration observed clinically is small. It might be useful if the K is too low or too high. So if K was 7meEg/L, it should be included in the calculation.
C. Based on the research done on what normal AG is, the span of population is from 8-10meq/L.

D. Figge equation: correction for albumin
So corrected AG= anion gap + 0.25 *( normal albumin- measured albumin (g/dl)
E. Interestingly the article points out from their review that the sensitivity of increased anion gap in detecting hyperlactatemia is very poor. Range is from 44% to 78%. If lactic acidosis is suspected, perhaps directly measuring that rather than relying on AG might be useful.
F. Baseline value for individuals AG to optimize the use of the calculation of AG in the detection of acidosis is what the authors suggest.

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