Anion Gap Calculation
Using the provided values (sodium 140 mmol/L, chloride 100 mmol/L, bicarbonate 19 mmol/L), the calculated anion gap is 21 mmol/L.
Calculation Method
The anion gap is calculated using the standard formula: AG = Na⁺ - (Cl⁻ + HCO₃⁻) 1, 2.
Using your values:
- AG = 140 - (100 + 19)
- AG = 140 - 119
- AG = 21 mmol/L
Clinical Interpretation
This represents an elevated anion gap, indicating high anion gap metabolic acidosis 1.
Normal Reference Range
- Normal anion gap: 8-12 mmol/L 1, 2
- Some sources cite up to 10-12 mmol/L as the upper limit of normal 3
Clinical Significance of AG = 21 mmol/L
With an anion gap of 21 mmol/L, this patient has moderate elevation suggesting:
- Mild-to-moderate DKA (diagnostic threshold >10-12 mmol/L) 1
- Early ethylene glycol poisoning (threshold for ECTR consideration is AG 23-27 mmol/L) 4
- Other causes of high anion gap metabolic acidosis including lactic acidosis, salicylate toxicity, methanol, or renal failure 1, 5
Important Caveats
Measurement variability: The 95% confidence interval for anion gap measurements can be substantial due to both analytical and biological variation 6. Real-world paired measurements show total observed variation of approximately ±6.0 mmol/L 6.
Albumin correction: Hypoalbuminemia can falsely lower the calculated anion gap, as albumin contributes significantly to unmeasured anions 7, 3. If albumin is low, the corrected anion gap would be higher than calculated.
Delta-delta analysis: To identify mixed acid-base disorders, calculate Δ anion gap/Δ bicarbonate 8, 9:
- Δ AG = 21 - 12 = 9 mmol/L
- Δ HCO₃⁻ = 24 - 19 = 5 mmol/L
- Ratio = 9/5 = 1.8
This ratio >1.6 suggests concurrent metabolic alkalosis in addition to the high anion gap acidosis 8, 9.