Differentials
Respiratory alkalosis
SIGNS / SYMPTOMS
Patients are most often asymptomatic.
Patients with liver cirrhosis or pregnancy commonly have respiratory alkalosis.
INVESTIGATIONS
The key to differentiating between RTA and respiratory alkalosis is the arterial blood pH. In RTA the pH is always low. When serum bicarbonate is low, an arterial pH of 7.37 or greater indicates the diagnosis is respiratory alkalosis.
Non-specific diarrhoea
SIGNS / SYMPTOMS
Diarrhoea.
INVESTIGATIONS
Patients differ from those with RTA due to the presence of a low urine pH and a large negative urine anion gap. Similar blood and urinary laboratory findings occur after the ingestion of ammonium chloride. The evidence of normal urinary acidification excludes RTA in these cases.
Diabetic ketoacidosis
SIGNS / SYMPTOMS
History of ongoing treatment of diabetic ketoacidosis with insulin and large volumes of sodium chloride infusion.
INVESTIGATIONS
The urine pH is low in diabetic ketoacidosis unless urine ketone excretion is extremely high.
Renal glycosuria
SIGNS / SYMPTOMS
May be confused with Fanconi syndrome. Patients with renal glycosuria exhibit glycosuria at normal serum glucose levels, but do not have acidaemia, bicarbonaturia, aminoaciduria, or phosphaturia. May be acquired or congenital.
INVESTIGATIONS
Normal serum bicarbonate and arterial pH, normal serum phosphate, and normal measurements of urinary bicarbonate, phosphate, and amino acid excretion.
Primary aminoacidurias
SIGNS / SYMPTOMS
May be confused with Fanconi syndrome. Patients with primary aminoacidurias demonstrate urinary excretion of one or more amino acids, but do not have acidaemia, glycosuria, or phosphaturia.
INVESTIGATIONS
Serum bicarbonate, urinary glucose, urinary phosphate excretion, serum phosphate, urine bicarbonate concentration are normal.
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