Proximal (type 2) renal tubular acidosis (RTA) is marked by reduced proximal bicarbonate reabsorption and urinary bicarbonate wasting. This may lead to an isolated non-anion gap metabolic acidosis or may occur in conjunction with other tubular defects leading to hypophosphatemia, glucosuria with normal plasma glucose concentration, hypouricemia, and/or aminoaciduria with generalized proximal dysfunction (Fanconi syndrome).

Major causes of proximal RTA in adults include increased excretion of immunoglobulins in the setting of monoclonal gammopathies and use of carbonic anhydrase inhibitors (eg, acetazolamide, and topiramate or ifosfamide). In children, proximal RTA may be caused by an autosomal recessive mutation in the gene for the sodium bicarbonate transporter (SLC4A4) or ifosfamide use, although in many cases, no cause is identified.

Related topic: Distal renal tubular acidosis