How is the osmolar gap calculated when the anion gap (AG) is elevated in the workup of metabolic acidosis?

Updated: Oct 10, 2018
  • Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

If the AG is elevated, the osmolar gap should be calculated by subtracting the calculated serum osmolality from the measured serum osmolality. Ethylene glycol and methanol poisoning increase the AG and the osmolar gap. Acetone, produced by decarboxylation of acetoacetate, can also raise serum osmolality. Other tests can be performed, including a screen for toxins (eg, ethylene glycol, salicylate) and tests for metabolic disorders (eg, ketoacidosis, lactic acidosis), that are known to elevate the AG.


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