What this calculator does
In a pure high anion-gap acidosis, every unit the gap rises should correspond to roughly one unit that bicarbonate falls, because the accumulating acid consumes bicarbonate as it appears. The delta ratio tests whether that one-for-one relationship holds.
When it does not, a second disorder is present. A ratio well below 0.4 points toward an additional normal-gap acidosis, and one above 2 toward a coexisting alkalosis, neither of which a single reading of either value would reveal.
The formula
The anion gap is calculated from sodium, chloride and bicarbonate. The rise in gap above 12 is divided by the fall in bicarbonate below 24, and the ratio is read against conventional bands.
| Term | Meaning |
|---|---|
| Delta ratio | The change in anion gap divided by the change in bicarbonate. |
| Mixed disorder | Two acid-base processes present at once, which the ratio can reveal. |
| Reference values | The calculation assumes a normal gap of 12 and normal bicarbonate of 24. |
The inputs explained
| Field | What to enter |
|---|---|
| Sodium (mEq/L) | Serum sodium in mEq/L. |
| Chloride (mEq/L) | Serum chloride in mEq/L. |
| Bicarbonate (HCO3) (mEq/L) | Serum bicarbonate in mEq/L, which appears in both halves of the ratio. |
When to use it
Investigating an acidosis
The ratio is the standard next step once a raised anion gap is found.
Detecting a second disorder
A mixed picture is easy to miss when each value is read on its own.
Learning acid-base interpretation
The delta ratio is a core part of systematic acid-base teaching.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does bicarbonate move the ratio?
The same sodium and chloride at three bicarbonate levels.
| Bicarbonate | Delta ratio | Anion gap used |
|---|---|---|
| 8 mEq/L | 1.25 | 32.0 mEq/L |
| 14 mEq/L | 1.40 | 26.0 mEq/L |
| 20 mEq/L | 2.00 | 20.0 mEq/L |
Questions
What do the bands mean?
Below 0.4 suggests a normal anion-gap acidosis, 0.4 to 0.8 a combined picture, 0.8 to 2 a pure high-gap acidosis, and above 2 a coexisting alkalosis or chronic respiratory acidosis. These are conventional guides, not sharp boundaries.
Why 12 and 24?
They are the assumed normal values for anion gap and bicarbonate. If your laboratory's reference range differs, or if albumin is low, the baseline gap changes and the ratio shifts with it.
Does albumin affect this?
Yes, and it matters. A low albumin lowers the baseline anion gap, so using 12 overestimates the rise and distorts the ratio. Correcting the gap for albumin first is generally recommended.
Can this be interpreted without clinical context?
No. The ratio narrows the possibilities from an electrolyte panel, but identifying which disorders are actually present requires the history, examination and other results. It is a reasoning aid for clinicians.
For the gap this builds on, see the anion gap calculator. For dissolved particle concentration, see the serum osmolality calculator.