Anion Gap of 11: Clinical Interpretation
An anion gap of 11 mmol/L is at the upper limit of normal using modern ion-selective electrode methodology and does not indicate a pathological high anion gap metabolic acidosis requiring urgent intervention. 1, 2
Understanding the Normal Range
The reference range for anion gap has shifted downward from the traditional 8-16 mmol/L to 3-11 mmol/L when using modern ion-selective electrode technology, primarily due to changes in chloride measurement calibration 2, 3
Your value of 11 mmol/L falls at the upper limit of this contemporary normal range and would be considered normal in most clinical laboratories using current methodology 2, 3
The traditional reference range of 8-16 mmol/L is outdated and can lead to misinterpretation if still being used clinically 2
Clinical Significance
An anion gap of 11 mmol/L does not meet criteria for high anion gap metabolic acidosis, which typically requires values exceeding 12 mmol/L before clinical concern arises 2
For toxic ingestions like ethylene glycol, the American College of Critical Care recommends extracorporeal treatment only when anion gap exceeds 27 mmol/L (strong recommendation) or is between 23-27 mmol/L (weak recommendation), far above your value 4, 1
In the context of ethylene glycol poisoning specifically, mortality was only 3.6% when anion gap remained below 28 mmol/L, compared to 20.4% when it exceeded this threshold 4
What to Do Next
Check arterial blood gases to determine if metabolic acidosis is actually present, as the anion gap alone does not confirm acidosis 1
Calculate the anion gap using the formula: Na+ + K+ - Cl- - HCO3- to ensure accurate calculation 1, 5
Consider the clinical context: obtain plasma glucose, serum ketones, lactate, renal function, and assess for symptoms of underlying conditions that could cause mild elevation 1
Important Caveats
A baseline low anion gap (from hypoalbuminemia or other causes) can mask a concurrent high anion gap acidosis, so always correlate with arterial blood gas results 5
The wide normal range (often 8-10 mmol/L) means that an increase in unmeasured anions can be present even without exceeding the upper limit of normal 6
Anion gaps exceeding 24 mmol/L are rare and strongly suggest metabolic acidosis requiring investigation 2