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ABG Interpretation
 
 

Gap-Gap Ratio

 
 
 
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Overview

The gap-gap ratio is used to further assess patients with a high anion gap metabolic acidosis (HAGMA).
In these patients, it is difficult to determine whether the HAGMA is the only process occurring, or whether there is additional process present such as a normal anion gap metabolic process, or a metabolic alkalosis.
The calculation essentially checks whether the change in anion gap from normal is equivalent to the change in the bicarbonate from normal - i.e. that all of the bicarbonate change is accounted for by a high anion gap process.
Gap-gap ratio
anion gap - 12 24 - HCO₃
The expected value for the gap-gap ratio (assuming a HAGMA) is 1.
  • Interpretation

  • Normal gap-gap (1) - isolated high anion gap metabolic acidosis.
  • Low gap-gap (<1) - coexistant high anion gap and normal anion gap metabolic acidoses.
  • High gap-gap (>1) - coexistant metabolic acidosis and metabolic alkalosis.
The gap-gap ratio is often used in diabetic ketoacidosis to determine whether an ongoing metabolic acidosis is due to ongoing ketoacidosis, or is due to isotonic saline infusion in the resuscitory period.
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