The urine anion gap can be helpful in the diagnosis of a patient with hyperchloremic metabolic acidosis.
For an acid urine:
urine anion gap =
= (urine sodium in mmol/L) + (urine potassium in mmol/L) - (urine chloride in mmol/L)
For an alkaline urine:
urine anion gap =
= (urine sodium in mmol/L) + (urine potassium in mmol/L) - (urine chloride in mmol/L) - (urine bicarbonate in mmol/L)
|
Urine AG
|
Urine pH
|
Plasma K
|
Diagnosis
|
|
negative
|
< 5.5
|
normal
|
normal
|
|
positive
|
< 5.5
|
elevated
|
selective aldosterone deficiency
|
|
positive
|
>= 5.5
|
elevated
|
hypkerkalemia distal renal tubular acidosis
|
|
positive
|
>= 5.5
|
normal or low
|
classic renal tubular acidosis
|
|
negative
|
>= 5.5
|
normal or low
|
GI bicarbonate loss
|
The higher the urine anion gap the lower the urinary ammonium concentration.
