Renal tubular acidosis

Renal tubular acidosis describes a group of transport defects in the kidney affecting the reabsorption of bicarbonate, the excretion of hydrogen ions or both.

Renal tubular acidosis results in
  • Hyperchloraemia
  • Metabolic acidosis
  • Normal anion gap
  • Normal/only slightly reduced eGFR

Renal tubular acidosis (RTA) are divided into:

Type 1 = Distal RTA

This is due to impaired secretion of hydrogen ions in the form of NH4+.
It is the most common form.
It is often associated with hypokalaemia.

Causes include:

Diagnosis is by oral acid load with ammonium chloride - the urine should become more acid, but in type 1 RTA the pH remains >5.5

Treatment: oral bicarbonate, possibly thiazide diuretic.

Type 2 = Proximal RTA

Type 2 RTA is due to impaired bicarbonate reabsoption in the proximal tubule.

Causes include:

Diagnosis is by IV bicarbonate loading - normally fractional excretion is <5% of the filtered load, but in type 2 RTA it is around 15%.

Treatment: oral bicarbonate.

Type 3 RTA = a combination of type 1 and type 2

Type 4 RTA = Hyperkalaemic RTA 

This is caused by hyperkalaemia impairing NH4+ formation

Causes are therefore any cause of hyperkalaemia, such as Addison’s or drug induced hyperkalaemia.

Treatment is to treat cause and control hyperkalaemia

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