see also:

• metabolic acidosis
• acid-base physiology
• wikipedia

• RTA is a group of conditions which cause a chronic metabolic acidosis due to either:
  • impaired ability to secrete hydrogen ions in the distal convoluted tubule (type I RTA)
  • impaired ability to absorb bicarbonate in the proximal convoluted tubule (type II RTA)
  • physiological reduction in distal tubular ammonium excretion, secondary to hypoaldosteronism (type IV RTA)
• renal tubular acidosis was first described in 1935 by Lightwood
• most common causes of RTA seen in the ED are:
  • chronic renal disease
  • toluene toxicity ⇒ hypokalaemia + rhabdomyolysis
  • inherited renal transport disorders
  • heavy metal toxicity
  • lithium

• urinary pH > 5.3 in a patient with serum bicarbonate ⇐ 20mmol/L

• inability to reduce urinary pH below 5.3
• decreased urinary citrate and hypercalciuria contributes to urolithiasis / renal stones / renal calculi, nephrocalcinosis and rickets/osteomalacia
• normal anion gap metabolic acidosis (although less severe cases may not cause acidosis “incomplete dRTA” diagnosed via the Short Ammonium Chloride Test)
• hypokalaemia

• severe hypokalaemia
• toxins: amphotericin, amiloride, lithium, and toluene
• autoimmune disease especially Sjögren's syndrome (SS) but also systemic lupus erythematosus (SLE)
• obstructive uropathy
• hereditary causes:
  • mutations of band 3 - AD or AR forms
  • mutations of apical proton pump - AR and maybe assoc. with sensorineural deafness
• cirrhosis
• nephrocalcinosis - while it may be caused by dRTA, dRTA may be caused by it via calcium-induced damage of the cortical collecting duct.
• renal transplantation
• sickle cell anaemia

• Rx with citrated bicarbonate decreases systemic acidosis and may prevent renal calculi formation and secondary bone disease

• can generate acidic urine thus acidosis less severe than type I RTA
• may be isolated or part of a syndrome of features called Fanconi syndrome:
  • polyuria, polydipsia, pRTA, phosphaturia, glycosuria, aminoaciduria, uricosuria, hypokalaemia, hyperchloremia and tubular proteinuria ⇒ osteomalacia due to phosphate wasting

• familial disorders:
  • cystinosis
  • other genetic diseases
• acquired disorders:
  • amyloidosis
  • multiple myeloma
  • paroxysmal nocturnal haemoglobinuria
  • toxins - lead, cadmium, ingesting expired tetracycline tablets

• a rare, transient, juvenile pattern of combined proximal and distal RTA
• also seen in carbonic anhydrase II deficiency

• type 4 RTA is not actually a tubular disorder at all and nor does it have a clinical syndrome similar to the other types of RTA described above.
• it was included in the classification of renal tubular acidoses as it is associated with a mild (normal anion gap) metabolic acidosis due to a physiological reduction in distal tubular ammonium excretion, which is secondary to hypoaldosteronism.
• its cardinal feature is hyperkalemia, and measured urinary acidification is normal.

• loss of renal cell mass > 70% (most commonly diabetic nephropathy)
• HIV / AIDS
• ACE inhibitors
• non-steroidal anti-inflammatory drugs (NSAIDs)
• cyclosporine

• drugs - aldosterone antagonists, trimethoprim, pentamidine
• pseudohypoaldosteronism

• primary adrenal insufficiency
• congenital adrenal hyperplasia
• aldosterone synthase deficiency