Feature

Type 1 RTA(Distal RTA)

Type 2 RTA(Proximal RTA)

Type 4 RTA(Hypoaldosteronism RTA)

Primary Defect

Failure of H⁺ secretion in distal tubule

Failure of HCO₃⁻ reabsorption in proximal tubule

Aldosterone deficiency or resistance

Main Pathophysiology (Reason)

Distal nephron cannot acidify urine

Proximal tubule cannot reclaim filtered bicarbonate

Reduced aldosterone → ↓ Na⁺ reabsorption → ↓ K⁺ & H⁺ secretion

Urine pH

> 5.5 (alkaline)

< 5.5 after acidosis develops

< 5.5

Why urine pH behaves this way?

Distal tubule unable to excrete H⁺

Distal acidification intact once plasma HCO₃⁻ falls

Distal acidification intact

Serum Potassium

Low (hypokalemia)

Low (hypokalemia)

High (hyperkalemia)

Reason for K⁺ abnormality

Impaired H⁺ secretion → ↑ K⁺ loss

Increased distal Na⁺ delivery → K⁺ wasting

↓ Aldosterone → ↓ K⁺ excretion

Acid–Base Disorder

Normal anion gap metabolic acidosis

Normal anion gap metabolic acidosis

Normal anion gap metabolic acidosis

Urinary Anion Gap

Positive

Variable

Positive

Stone Formation

Common

Rare

Rare

Reason for stones

Alkaline urine + ↓ citrate → calcium phosphate stones

Urine not persistently alkaline

Urine acidic

Nephrocalcinosis

Yes

No

No

Bone Disease

Osteomalacia / rickets

Osteomalacia / rickets

Rare

Common Causes

Autoimmune diseases, amphotericin B, analgesic nephropathy

Fanconi syndrome, drugs (tenofovir, acetazolamide), multiple myeloma

Diabetes mellitus, ACEI/ARB, NSAIDs, adrenal disease

Key Diagnostic Clue

Metabolic acidosis + alkaline urine

Acidosis improves as HCO₃⁻ drops

Acidosis + hyperkalemia

Treatment Principle

Alkali therapy (bicarbonate/citrate)

Large-dose bicarbonate

Treat hyperkalemia + mineralocorticoids