Acid base problems

In response to acidosis, the kidneys do two things:

1. Reabsorb all filtered bicarbonate
2. Excrete excess acid by increasing levels of NH₄⁺ in the urine

In renal tubular acidosis, one of these processes fails.

Previously RTA was classified under one of the following headings:

• Type I or distal RTA
• Type II or proximal RTA
• Type IV or hyperkalaemic distal RTA

A clearer understanding of the underlying defects allows for a different approach to diagnosis:

RTA with excessive excretion of bicarbonate

• Proximal RTA
• Acetazolamide use

Low excretion of NH₄⁺(Distal RTA)

• Reduced availability of ammonia in the renal medulla secondary to
• Decreased ammonia generation due to low GFR or hyperkalaemia
• Medullary-interstitial disease
• Reduced secretion of H⁺ in the collecting duct due to
• Failure of the H⁺ pump
• Back leak of H⁺ from the tubular lumen into the tubular cell
• Failure of voltage augmentation of distal H⁺ secretion

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