Patients with renal tubular acidosis (RTA) are often asymptomatic but may present with complaints of muscular weakness related to associated hypokalemia.
Patients with severe acidemia can show hyperventilation or Kussmaul breathing due to respiratory compensation.
Patients with RTA have a low arterial pH and serum bicarbonate with hyperchloremia and a normal serum anion gap.
The urine pH exceeds 5.5 in classic distal RTA, but is lower than 5.0 in patients with untreated proximal RTA and is low also in hyperkalemic distal RTA.
Alkali therapy is the mainstay of treatment.
Potassium supplementation may be required for hypokalemia, and low-potassium diets are used if hyperkalemia is present.
If hyperkalemic 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.
Proximal RTA occurs most often as a component of Fanconi syndrome, which is characterized by generalized dysfunction of the proximal tubule, with the resultant urinary loss of bicarbonate, calcium, phosphate, urate, amino acids, glucose, and other organic acids and bases.
In children, Fanconi syndrome causes growth retardation, renal rickets, and severe metabolic acidosis. Adult cases exhibit similar urinary losses, but the clinical impact is largely restricted to metabolic acidosis.
Fanconi syndrome is marked by the appearance in the urine of all amino acids. Specific amino aciduria as seen in isolated cystinuria, glucose loss in isolated glycosuria, and isolated phosphaturia do not constitute Fanconi syndrome.
The term renal tubular acidosis (RTA) describes any one of a number of disorders, in which the excretion of fixed acid (distal RTA) or the reabsorption of filtered bicarbonate (proximal RTA) is impaired to a degree that is disproportionate to any existing impairment of the glomerular filtration rate.  The acid retention or bicarbonate loss results in the development of hyperchloremic metabolic acidosis marked by hypobicarbonatemia and depressed arterial blood pH. In the absence of other acid-base disorders the serum anion gap is normal. Either hypokalemia or hyperkalemia may be present, depending on the nature of the acidification defect.
Fanconi syndrome is characterized by a generalized dysfunction of the renal proximal tubule that results in the urinary loss of substances normally reabsorbed by the kidney at this site. The substrates lost include bicarbonate, glucose, amino acids, phosphate, small proteins and peptides, and organic acids and bases. Salt wasting, volume depletion, and potassium wasting often develop as secondary effects. The pathophysiologic basis of these abnormalities depends upon the specific cause of the individual patient’s Fanconi syndrome.
Texas Tech University Health Sciences Center
MEL declares that he has no competing interests.
Dr Melvin E. Laski would like to gratefully acknowledge Dr Elizabeth Cobb, Dr Rebin Titus, and Dr Abeer Kaldas, previous contributors to this monograph. EC and AK declare that they have no competing interests; RT's competing interests are not disclosed.
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