Hyperkalemic (Type 4) Renal Tubular Acidosis (RTA)

Definition and EtiologyTop

Type 4 renal tubular acidosis (RTA) is also referred to as hyperkalemic RTA. The hallmark of this disease is hypoaldosteronism manifested by mild-to-moderate hyperkalemia and a very mild hyperchloremic (non–anion gap) metabolic acidosis, usually resulting from aldosterone deficiency or tubular resistance to aldosterone.

The etiologies of type 4 RTA can be divided into aldosterone underproduction and aldosterone resistance. Selected etiologies of type 4 RTA: Table 1.

DiagnosisTop

Hyperkalemia and a mild hyperchloremic metabolic acidosis are the major manifestations of type 4 RTA. The diagnosis of type 4 RTA should be considered in any patient with these findings present persistently in the absence of other etiologies of hyperkalemia, such as chronic kidney disease or the use of potassium supplements.

Careful examination of the medical history and medication list should be carried out to ensure the patient is not taking any medications or does not have an undiagnosed disorder known to cause type 4 RTA.

Diagnostic Tests

Various etiologies can be differentiated by measurement of plasma renin activity (PRA) and serum aldosterone and cortisol concentrations. These tests should be performed following the administration of a loop diuretic or after assuming the upright position for 3 hours, which are known to increase renin and aldosterone release in healthy individuals.

Careful assessment of these values should be performed to elucidate the underlying etiology. Renin and aldosterone concentrations depending on etiology: Table 1.

A general approach to RTA based on results of urinary studies: Table 2.

TreatmentTop

Unlike in other RTAs, no bicarbonate replacement therapy is usually required, as acidosis is only mild.

Management of type 4 RTA depends on underlying disease, which should be treated if possible. Hyporeninemic hypoaldosteronism can be treated with fludrocortisone in doses significantly higher than those used for adrenal insufficiency. However, most of these patients have hypertension and edema, which can be exacerbated with mineralocorticoid replacement. In such cases a low-potassium diet combined with a loop diuretic or thiazide-type diuretic can be used to control hyperkalemia. Patients with primary adrenal insufficiency should receive glucocorticoid and mineralocorticoid replacement.

TablesTop