Diagnosis
Arterial blood gas sampling is essential for the diagnosis. If the pH is low (under 7.35) and the bicarbonate levels are decreased (<24 mmol/l), metabolic acidemia is present, and metabolic acidosis is presumed. Due to respiratory compensation (hyperventilation), carbon dioxide is decreased and conversely oxygen is increased. An ECG can be useful to anticipate cardiac complications.
Other tests that are relevant in this context are electrolytes (including chloride), glucose, renal function and a full blood count. Urinalysis can reveal acidity (salicylate poisoning) or alkalinity (renal tubular acidosis type I). In addition, it can show ketones in ketoacidosis.
To distinguish between the main types of metabolic acidosis, a clinical tool called the anion gap is considered very useful. It is calculated by subtracting the chloride and bicarbonate levels from the sodium.
Anion gap = ( + ) - ( + )
As sodium is the main extracellular cation, and chloride and bicarbonate are the main anions, the result should reflect the remaining anions. Normally, this concentration is about 8-16 mmol/l (12±4). An elevated anion gap (i.e. > 16 mmol/l) can indicate particular types of metabolic acidosis, particularly certain poisons, lactate acidosis and ketoacidosis.
As the differential diagnosis is made, certain other tests may be necessary, including toxicological screening and imaging of the kidneys. It is also important to differentiate between acidosis-induced hyperventilation and asthma; otherwise, treatment could lead to inappropriate bronchodilation.
Read more about this topic: Metabolic Acidosis