Anion Gap Calculation
Your anion gap is 4.4 mmol/L using the standard formula (Na+ + K+ - Cl- - HCO3-), which is within the modern normal range of 3-11 mmol/L. 1
Calculation Method
Using the values provided:
- Sodium: 136 mmol/L
- Potassium: 3.4 mmol/L
- Chloride: 106 mmol/L
- Bicarbonate (CO2): 29 mmol/L
Anion Gap = Na+ + K+ - Cl- - HCO3- = 136 + 3.4 - 106 - 29 = 4.4 mmol/L 2, 1
Clinical Interpretation
This anion gap of 4.4 mmol/L is normal based on current ion-selective electrode methodology, which has a reference range of 3-11 mmol/L (or 5-12 mmol/L in some laboratories). 3
The older reference range of 8-16 mmol/L is outdated and should not be used, as it was based on different laboratory techniques. 3
Your bicarbonate of 29 mmol/L is slightly elevated (normal range typically 22-26 mmol/L), which may indicate a metabolic alkalosis rather than acidosis. 2
Clinical Significance of This Result
A normal anion gap rules out high anion gap metabolic acidosis (HAGMA), which includes conditions like diabetic ketoacidosis, lactic acidosis, renal failure, and toxic ingestions. 4
An anion gap below 3 mmol/L would be considered low and could suggest conditions like hypoalbuminemia, multiple myeloma with IgG paraproteins, or laboratory error. 3, 5
Negative anion gaps (≤ -1 mmol/L) are rare and typically indicate laboratory error, specimen contamination, extreme hyperkalemia, bromism, or paraproteinemia. 6
Important Caveats
Do not apply albumin correction formulas to the anion gap, as the law of electroneutrality ensures hypoalbuminemia is already accounted for in the original calculation, and correction formulas may increase misinterpretation risk. 7
If metabolic acidosis were present with this normal anion gap, it would suggest a hyperchloremic (non-anion gap) metabolic acidosis from causes like diarrhea, renal tubular acidosis, or ureterosigmoidostomy. 4