Appropriate Tests


Blood gas arterial, Electrolytes, Anion gap, Creatinine, Urea, pH, Bicarbonate, Haemoglobin (FBC). Plasma proteins, phosphate, Electrolytes, specific drug levels eg aspirin, methanol, ethylene glycol, Liver function tests, Blood and urine glucose, Ketones, Lactate, Osmolality.

See also Alkalosis.

Metabolic acidosis

Defined as acidosis with negative base excess and decreased bicarbonate.

Increased anion gap


Renal failure



ß-hydroxybutyrate is the preferred test, rather than acetoacetate.

Lactic acidosis



Serum and urine drug and other assays, as appropriate.

  • Salicylate

Salicylate, Lactate.

  • Methanol

Methanol (see under Alcohols).

  • Ethylene glycol

Glycol, Oxalate urine.

Normal anion gap

Hyperchloraemic acidosis.

Renal tubular acidosis

Urea, Creatinine

Intestinal bicarbonate loss, especially

  • Diarrhoea
  • Intestinal fistula

Culture or multiplex PCR stool sample for bacterial, viral or parasitic pathogens (discuss with local laboratory for test availability).

Compensatory, especially

In primary respiratory alkalosis.

Unexplained acidosis in childhood

See Organic acidaemias.

Respiratory acidosis

Defined as acidosis with an increased pCO2.

Respiratory failure (acute/chronic)



In primary metabolic alkalosis.

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