Expansion
Type 1 distal, type 2 proximal, type 4 hypoaldosteronism
Expansion
All produce a normal anion gap (hyperchloraemic) metabolic acidosis.
| Type | Defect | Potassium | Urine pH | Notes |
|---|---|---|---|---|
| Type 1 (distal) | Cannot secrete hydrogen ions | Low | Above 5.3 always | Stones and nephrocalcinosis; Sjogren, amphotericin |
| Type 2 (proximal) | Cannot reabsorb bicarbonate | Low | Variable; low once serum bicarbonate falls | Part of Fanconi syndrome; myeloma, acetazolamide |
| Type 4 | Aldosterone deficiency or resistance | High | Usually under 5.5 | Diabetes, ACE inhibitors, spironolactone, Addison |
(Type 3 is a rare mixed form and is little used.)
Type 1 is the one that causes stones, because persistently alkaline urine with hypercalciuria and low citrate favours calcium phosphate precipitation.
Type 4 is the commonest in practice, typically in diabetic patients with hyporeninaemic hypoaldosteronism, and the acidosis is usually mild.
The urinary anion gap (sodium plus potassium minus chloride) helps: it is positive in renal tubular acidosis, since ammonium excretion is impaired, and negative in diarrhoea.