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

Patients in the intensive care unit often develop anion gap metabolic acidosis most commonly from lactic acidosis. Clinicians routinely measure serum lactate levels, but it is not clear if one is able to use the measured serum lactate level to determine if there is a second cause for anion gap metabolic acidosis in these critically ill patients. In this report, 503 episodes of lactic acidosis with serum lactate levels greater than 5 mmol/L at a single institution over two years were analyzed. The average serum anion gap minus serum lactate level in these patients was 6.9 ± 0.21 mEq/L, the average corrected anion gap was -1.3 ± 0.23 mEq/L and the average strong ion gap was 5.1 ± 0.3 mEq/L. The majority of the episodes with anion gap-serum lactate concentration >8.0 mEq/L were explained by elevated serum albumin concentration, elevated serum phosphorus concentration, presence of ketones in the urine or high β-hydroxybutyrate concentrations. The above data suggest that one can use the measured serum lactate concentration and subtract from the serum anion gap to determine if there is a second reason for anion gap metabolic acidosis.