Approach to the patient with renal tubular acidosis

The renal tubular acidoses are a collection of syndromes characterized by defective urinary acidification. These syndromes have classically caused some confusion, and many opine that the widely used numerical system (type 1, 2) should be abandoned. We consider distal renal tubular acidosis and proximal renal tubular acidosis separately, and briefly cover hypoaldosteronism. Distal (Type 1) renal tubular acidosis is a syndrome of hypokalaemia, metabolic acidosis, kidney stones, nephrocalcinosis, and osteomalacia or rickets. It is caused by failure of the acid secreting α‎‎‎-intercalated cells in the distal nephron. Proximal (Type 2) renal tubular acidosis is a syndrome of metabolic acidosis that is almost always accompanied by the Fanconi syndrome of glycosuria, phosphaturia, uricosuria, aminoaciduria, and low-molecular-weight proteinuria. It is caused by a failure of bicarbonate reabsorption by the proximal tubular cells. Type 3 or mixed renal tubular acidosis, as originally described, has vanished (or was originally incompletely described). It is sometimes used to describe a mutation of carbonic anhydrase II, which causes both proximal and distal renal tubular acidosis, as well as cerebral calcification and osteopetrosis. Type 4 or hypoaldosteronism is a syndrome of hyperkalaemia and mild metabolic acidosis. It is due to a lack of aldosterone or resistance to its action.