How this calculator works
Use samples collected together. The measured pH describes acidity; the reconstructed pH is a consistency check, not an independent measurement. The anion gap excludes potassium. The respiratory comparison is shown only when bicarbonate is below 24 mmol/L and assumes a primary metabolic acidosis. Mixed disorders require clinical assessment. The result is an estimate for information only and is not medical advice.
Formula
pH = 6.1 + log10(HCO3 / (0.03 PCO2)); AG = Na - Cl - HCO3; adjusted AG = AG + 0.25(40 - albumin in g/L). Expected PCO2 = 1.5 HCO3 + 8 ± 2 mmHg.
Worked example
Na 140, Cl 104 and bicarbonate 14 mmol/L give AG 22. With albumin 30 g/L, adjusted AG is 24.5. Expected PCO2 is 29 mmHg, with a range of 27 to 31.
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Frequently asked questions
Why enter both measured and calculated pH?
A discrepancy can reflect sampling time, measurement methods or inconsistent inputs. Check the laboratory report before interpreting it.
Does a pH within range rule out a disorder?
No. Opposing processes may leave pH within range even when bicarbonate, CO2 and the anion gap are abnormal.
Which CO2 units work?
Choose mmHg or kPa and enter the corresponding number. One mmHg equals 0.133322387415 kPa.