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Interpretation
- High anion gap metabolic acidosis
Anion gap
28.0
Corrected AG
–
Delta ratio
1.00
1 · Is the gas internally consistent?
Yes
Henderson–Hasselbalch pH from pCO₂ and HCO₃⁻ = 7.18 (measured 7.18). Within 0.05, so the values agree.
2 · Acidaemia or alkalaemia?
Acidaemia
pH 7.18 (normal 7.35–7.45).
3 · What is the primary process?
Metabolic acidosis (low HCO₃⁻)
pCO₂ 22 mmHg (35–45), HCO₃⁻ 8 mmol/L (22–26).
4 · Is compensation appropriate? (Winter's formula)
Appropriate respiratory compensation
Expected pCO₂ = 1.5 × 8 + 8 ± 2 = 18–22 mmHg; measured 22.
5 · Anion gap
High anion gap (28): high anion gap metabolic acidosis present
AG = Na⁺ − (Cl⁻ + HCO₃⁻) = 134 − (98 + 8) = 28 (normal 8–12). Add albumin to correct the gap: each 1 g/dL fall lowers the AG by about 2.5.
6 · Delta ratio: anything else hiding?
Delta ratio 1.00: 0.8–2: pure high anion gap acidosis (DKA often ~1, lactic ~1.6)
(AG − 12) ÷ (24 − HCO₃⁻) = (28 − 12) ÷ (24 − 8).
What next?
High AG: check lactate, ketones (capillary β-hydroxybutyrate), urea/creatinine, and an osmolar gap if toxic alcohol is possible (GOLDMARK).
Rules used
- Normal: pH 7.35–7.45, pCO₂ 35–45 mmHg, HCO₃⁻ 22–26 mmol/L, anion gap 8–12 (no K⁺).
- Metabolic acidosis: expected pCO₂ = 1.5 × HCO₃⁻ + 8 ± 2 (Winter's). Metabolic alkalosis: 0.7 × HCO₃⁻ + 21 ± 2.
- Respiratory acidosis: HCO₃⁻ +1 (acute) or +3.5 (chronic) per 10 mmHg rise in pCO₂. Respiratory alkalosis: −2 (acute) or −5 (chronic) per 10 mmHg fall.
- Albumin-corrected AG = AG + 2.5 × (4 − albumin g/dL). Delta ratio = (AG − 12) ÷ (24 − HCO₃⁻).
Learn the approach in Acid–base: stepwise interpretation. Educational tool; interpret with the clinical picture.