Renal tubular acidosis

Renal tubular acidosis (RTA) is a clinical syndrome characterised by hyperchloraemic metabolic acidosis with a normal serum anion gap.

Adult patients with RTA are often asymptomatic but may present with muscular weakness related to associated hypokalaemia, nephrocalcinosis, or recurrent renal stones.

There are four types of RTA: classic distal RTA (type I), proximal RTA (type II), hyperkalaemic distal RTA (type IV), and a rare combination of proximal and distal RTA caused by carbonic anhydrase II deficiency and carbonic anhydrase inhibitors blocking the metabolism of bicarbonate and carbonic acid (type III).

Alkali therapy is the mainstay of treatment in all forms of RTA.

If hyperkalaemic distal RTA is due to mineralocorticoid deficiency, fludrocortisone can be given unless it is contraindicated due to the presence of fluid overload or uncontrolled hypertension.

The term renal tubular acidosis (RTA) describes a group of disorders of acid-base homeostasis, in which the primary impairment is the excretion of fixed acid (distal RTA) or the reabsorption of filtered bicarbonate (proximal RTA).[1]Palmer BF, Kelepouris E, Clegg DJ. Renal tubular acidosis and management strategies: a narrative review. Adv Ther. 2021 Feb;38(2):949-68. https://www.doi.org/10.1007/s12325-020-01587-5 http://www.ncbi.nlm.nih.gov/pubmed/33367987?tool=bestpractice.com The acid retention or bicarbonate loss results in hyperchloraemic metabolic acidosis marked by low serum bicarbonate and a normal anion gap. Either hypokalaemia or hyperkalaemia may be present, depending on the nature of the acidification defect. 

Fanconi syndrome is due to dysfunction of the renal proximal tubule resulting in the urinary loss of substances normally reabsorbed by the kidney at this site, such as bicarbonate, glucose, amino acids, phosphate, small proteins, and uric acid.[2]Kashoor I, Batlle D. Proximal renal tubular acidosis with and without Fanconi syndrome. Kidney Res Clin Pract. 2019 Sep 30;38(3):267-81. https://www.doi.org/10.23876/j.krcp.19.056 http://www.ncbi.nlm.nih.gov/pubmed/31474092?tool=bestpractice.com Salt wasting, volume depletion, and potassium wasting often develop as secondary effects. The pathophysiological basis of these abnormalities depends upon the specific cause of the individual patient’s Fanconi syndrome.