Show Summary Details
Page of

The renal tubular acidoses 

The renal tubular acidoses

The renal tubular acidoses

Fiona E. Karet



Further reading updated.

Updated on 25 May 2011. The previous version of this content can be found here.
Page of

PRINTED FROM OXFORD MEDICINE ONLINE ( © Oxford University Press, 2015. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Medicine Online for personal use (for details see Privacy Policy).

date: 28 April 2017

Renal tubular acidosis (RTA) arises when the kidneys either fail to excrete sufficient acid, or are unable to conserve bicarbonate, both circumstances leading to metabolic acidosis of varying severity with altered serum potassium. Proximal and distal types of RTA can be differentiated according to which nephron segment is malfunctioning. The condition may be secondary (e.g. associated with drugs, autoimmune disease, or diabetes mellitus) or inherited, and there may be renal tract calcification and—in chronic cases—metabolic bone disease.

Proximal RTA

Aetiology and diagnosis – the condition may be (1) secondary to generalized proximal tubular dysfunction (part of the renal Fanconi syndrome), or rarely (2) due to inherited mutation of a single transporter (NBC1) located at the basolateral surface of the proximal tubular epithelium. The combination of normal anion gap acidosis with other features of proximal tubular dysfunction such as renal phosphate wasting (and hypophosphataemia), renal glycosuria, hypouricaemia (due to uricosuria), aminoaciduria, microalbuminuria, and other low-molecular-weight proteinuria suggests the diagnosis.

Management—this requires large quantities of oral alkali (as bicarbonate or citrate), with (in most cases) potassium supplements to prevent severe hypokalaemia. Associated phosphate and vitamin D deficiencies may also require treatment. Precipitating drugs should be stopped if possible.

Distal RTA

Aetiology—two main classes are differentiated by whether (1) the acid-handling cells (α‎-intercalated cells) in the collecting ducts are themselves functioning inadequately, in which case there is associated hypokalaemia (this is ‘classic’ distal RTA); or (2) the main abnormality is of the salt-handling principal cells in the same nephron segment, in which case hyperkalaemia occurs and the acidosis is a secondary phenomenon. This is hyperkalaemic distal RTA, which is most often secondary to hyporeninaemic hypoaldosteronism (e.g. in diabetes mellitus or critical illness) but may also be reversibly precipitated by drugs such as trimethoprim or ciclosporin.

Diagnosis—the combination of normal anion gap acidosis with a urine pH higher than 5.5 suggests classic distal RTA, especially if renal tract calcification is present or there is coexistent autoimmune disease. Diagnosis may require an oral urine acidification test if the metabolic abnormalities are partially masked by compensatory mechanisms, when inability to achieve a urine pH less than 5.5 clinches the diagnosis of classic distal RTA. By contrast, urine-acidification capacity is normal in hyperkalaemic distal RTA.

Management—(1) Classic distal RTA—1 to 3 mg/kg per day of oral alkali (additional supplements should not be required); (2) Hyperkalaemic distal RTA—treatment is with sodium bicarbonate, but fludrocortisone and/or potassium-lowering measures may also be necessary. Precipitating drugs should be stopped.

Access to the complete content on Oxford Medicine Online requires a subscription or purchase. Public users are able to search the site and view the abstracts for each book and chapter without a subscription.

Please subscribe or login to access full text content.

If you have purchased a print title that contains an access token, please see the token for information about how to register your code.

For questions on access or troubleshooting, please check our FAQs, and if you can't find the answer there, please contact us.