Delta Ratio Acid-Base Calculator

How it is calculated

The tool compares how far the anion gap has risen with how far bicarbonate has fallen: delta ratio = (anion gap − normal anion gap) ÷ (normal HCO₃ − measured HCO₃). All values are in mmol/L. If you leave the reference boxes empty it uses a normal anion gap of 12 and a normal bicarbonate of 24; both can be changed to match your laboratory. It prints the ratio, the delta gap (numerator), the delta bicarbonate (denominator) and a one-line reading: below 0.4, a coexisting normal-gap acidosis; 0.4 to 1.0, a mixed high-gap and normal-gap acidosis; above 1.0 up to 2.0, an uncomplicated high anion gap acidosis; above 2.0, a coexisting metabolic alkalosis or chronic respiratory acidosis. The ratio only makes sense when there is an acidosis with a raised gap, so if bicarbonate is at or above the normal value, or the anion gap is at or below normal, no result is shown. Negative values are rejected too. The reading appears in the language of the page and is for education, not diagnosis.

Common mistakes

• Using the ratio when there is no high anion gap acidosis to begin with. With a bicarbonate of 26 or an anion gap of 8 (defaults 24 and 12) the tool shows nothing, because there is no gap rise or bicarbonate fall to compare.
• Leaving the default normal anion gap of 12 when your laboratory's anion gap is calculated differently, for example with potassium included, or has another reference range. That shifts the delta gap and the ratio.
• Entering the albumin-corrected anion gap in one calculation and the uncorrected gap in the next, then comparing the ratios as if they were the same.
• Reading a single ratio as a diagnosis. It is a screen for a second disorder and has to be read with the clinical picture and the blood gas.
• Treating 1.0 as the edge of normal. A ratio of exactly 1.0 sits in the 0.4 to 1.0 band, and small changes in either input can move the reading across a band.