Learner decision: where the numbers do not close

An arterial result shows pH 7.20, PaCO2 26 mmHg, HCO3− 10 mmol/L, Na 140 mmol/L, Cl 110 mmol/L, albumin 4.0 g/dL, and lactate 3.2 mmol/L. The pH and HCO3− indicate primary metabolic acidosis. Winter's formula gives expected PaCO2 = 1.5 × 10 + 8 ± 2 = 23 ± 2 mmHg, or 21–25 mmHg. Observed PaCO2 26 mmHg is just above that range and needs specimen, method, trend, and clinical review; the range is not proof of compensation or diagnosis.

Anion gap is Na − (Cl + HCO3−) = 140 − (110 + 10) = 20 mmol/L. The delta ratio is (20 − 12) / (24 − 10) = 0.57. One published band places that below 0.8 and suggests concurrent normal-anion-gap acidosis, but published bands differ and local policy controls the interpretation.

The bounded statement is elevated-anion-gap metabolic acidosis with evidence that may fit a normal-anion-gap component and a PaCO2 requiring range review. Calling it compensated from directions alone or ignoring delta screening because the gap is elevated is unsafe. Report calculations, method policy, and remaining evidence needed when the mixed-process screen is positive.