Etiology and Pathogenesis
Type IV RTA is caused by either an absolute or relative deficiency in aldosterone secretion, leading to reduced excretion of H+ and K+ in the collecting ducts. This results in hyperkalemia and hyperchloremic metabolic acidosis with a normal anion gap (AG).
Based on the underlying mechanism, it can be classified as:
- Absolute aldosterone deficiency: Caused by hyporeninemia or hypoaldosteronism.
- Relative aldosterone deficiency: Caused by reduced responsiveness to aldosterone.
Based on the etiology, it can be divided into congenital and secondary forms.
Clinical Manifestations
Type IV RTA primarily presents with hyperkalemia and hyperchloremic metabolic acidosis with a normal anion gap. Congenital cases are rare. Secondary cases are often associated with mild to moderate renal insufficiency, but the severity of acidosis and hyperkalemia is disproportionate to the degree of renal impairment. Urinary ammonium (NH4+) excretion is reduced.
Diagnosis
The diagnosis of type IV RTA is based on the presence of hyperkalemia, hyperchloremic metabolic acidosis with a normal anion gap, and reduced urinary ammonium (NH4+). Serum aldosterone levels may be decreased or normal.
Treatment
Treatment options include:
- Discontinuation of medications that impair aldosterone synthesis or activity.
- Use of oral cation exchange resins or loop diuretics to promote potassium excretion. Dialysis may be required in severe cases.
- Correction of acidosis with oral or intravenous sodium bicarbonate. When administered intravenously, careful monitoring of blood volume is required, and loop diuretics may be co-administered to reduce volume overload.
For patients with aldosterone deficiency who do not have hypertension or significant volume overload, corticosteroids such as fludrocortisone (0.1 mg/day) may be used.