Characteristics of the different types of renal tubular acidosis (RTA)

	Hypokalemic RTA		Hyperkalemic RTA
	Type 1 RTA (distal RTA)	Type 2 RTA (proximal RTA)	Type 4 RTA (hypoaldosteronism)	Distal tubule sodium transport defects
Primary defect	Impaired distal tubule/collecting duct acidification.	Reduced proximal HCO₃ reabsorption.	Decreased aldosterone secretion or aldosterone resistance.	Reduced sodium reabsorption unrelated to aldosterone.
Plasma HCO₃	Variable. May be below 10 mEq/L.	Usually 12 to 20 mEq/L.	Usually greater than 17 mEq/L.	Usually greater than 17 mEq/L.
Urine pH	Always >5.3.	Variable. Greater than 5.3 during periods of bicarbonaturia usually related to therapeutic increases in serum [HCO₃]. Otherwise <5.3.	Variable. Usually greater than 5.3.	Variable. Usually greater than 5.3.
Plasma potassium	Usually reduced and generally corrects with alkali therapy.	May be normal or reduced; worsened by bicarbonaturia induced by alkali therapy.	Increased.	Increased.
Urine anion gap (UAG)/urine osmolal gap (UOG)	UAG >20 mEq/L or UOG <150 mosm/kg. Consistent with low urine ammonium concentration.	Variable.	UAG >20 mEq/L or UOG <150 mosm/kg. Consistent with low urine ammonium concentration.	UAG >20 mEq/L or UOG <150 mosm/kg. Consistent with low urine ammonium concentration.
Urine Ca/Cr ratio	Increased	Normal	Normal	Normal
Nephrolithiasis/nephrocalcinosis	Yes	No	No	No

HCO₃: bicarbonate; Ca/Cr: calcium/creatinine.

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