Can one use serum Lactate Concentration to Correct for the Anion gap?

Area of Science:

• Critical Care Medicine
• Nephrology
• Biochemistry

Background:

• Anion gap metabolic acidosis is common in intensive care unit (ICU) patients, often due to lactic acidosis.
• Serum lactate is routinely measured, but its utility in identifying other causes of acidosis is unclear.

Purpose of the Study:

• To determine if measured serum lactate levels can help identify secondary causes of anion gap metabolic acidosis in critically ill patients.

Main Methods:

• Analysis of 503 episodes of lactic acidosis (serum lactate >5 mmol/L) over two years at a single institution.
• Calculation of serum anion gap minus serum lactate, corrected anion gap, and strong ion gap.

Main Results:

• The average serum anion gap minus serum lactate was 6.9 mEq/L.
• Episodes with anion gap-serum lactate >8.0 mEq/L were often explained by elevated albumin, phosphorus, ketones, or β-hydroxybutyrate.
• Average corrected anion gap was -1.3 mEq/L and average strong ion gap was 5.1 mEq/L.

Conclusions:

• Subtracting serum lactate from the serum anion gap can help identify additional causes of anion gap metabolic acidosis in ICU patients.
• Elevated albumin, phosphorus, ketones, or β-hydroxybutyrate are common secondary causes when the anion gap-lactate difference is high.