In nephrology, the delta ratio, or "delta-delta" (denoted Δ/Δ), is a formula that can be used to evaluate whether a mixed acid–base disorder (metabolic acidosis) is present, and if so, assess its severity.
A low anion gap is usually an oddity of measurement, rather than a clinical concern.
Results 1. and 4. are oddities, mathematically speaking:[citation needed] Result 1: if there is a normal anion gap acidosis, the (AG – 12) part of the equation will be close to zero, the delta ratio will be close to zero and there is no mixed acid–base disorder.
A normal anion gap acidosis (NAGMA) has more to do with a change in [Cl−] or [HCO−3] concentrations.
For a list of the common causes of this change in bicarbonate or chloride, see normal anion gap acidosis.
KULT is probably the easiest of the mnemonics to use (Ketones, Uremia, Lactate, Toxins).
Metformin as a pure toxicological cause is vanishingly rare.
[citation needed] Result 4: if the result of the ratio is greater than 2 in a high anion gap metabolic acidosis, it is usually because there was a pre-existing higher than normal bicarbonate level.
This is commonly found in people with chronic respiratory acidosis from chronic lung disease such as chronic obstructive pulmonary disease (COPD), who can't breathe off their excess carbon dioxide owing to poor lung function, and retain bicarb in order to counteract the acidosis caused by the retained CO2.
Alternatively it could be caused by a concurrent metabolic alkalosis such as vomiting causing acid loss and hence alkalosis, or diuretic use with loss of [Cl−] and a compensatory bicarb retention in order to maintain plasma electrical neutrality.
When this happens the numerator is large, the denominator is small, and the result is a delta ratio which is high (>2).
[citation needed] Result 3: if there is a pure HAGMA, the bicarb would be expected to fall at a similar rate as the anion gap rises, since one molecule of acid combines with one molecule of bicarb buffer.
Since the anions are unable to diffuse out of the bloodstream, while bicarbonate and hydrogen ions diffuse with ease (as H2CO3, carbonic acid), the usual result will be closer to a delta ratio of 1 to 2.
[5] Result 2: if the delta ratio is somewhere between low (<0.4) and high (1–2), then it is usually due to a combination of high anion gap metabolic acidosis and normal anion gap acidosis.
[6] For example, a person with cholera may have a normal anion gap acidosis due to diarrhea, but becomes progressively dehydrated and develops a lactic acidosis from shock, and proceeds to develop a high anion gap metabolic acidosis – i.e. a mixed acid–base disorder.