Which chemical imbalances are found in Fanconi syndrome?

Updated: Feb 09, 2018
  • Author: Sahar Fathallah-Shaykh, MD; Chief Editor: Craig B Langman, MD  more...
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Hypokalemia is the result of urinary losses secondary to increased secretion of potassium, which is stimulated by the delivery of large amounts of sodium and fluid to the distal nephron. Acidosis contributes to this outcome by increasing the filtered load of potassium. Potassium depletion may result in muscle weakness, constipation, and, when severe, sudden death. In addition, hypokalemia contributes to the defect in urine concentration ability seen in these patients.

Hypophosphatemia is secondary to the impairment in proximal tubular reabsorption. However, an increase in phosphate excretion can be observed only during the initial phase of the syndrome. Subsequently, a new steady state is reached whereby the amount of phosphate present in the urine closely matches the intake. No defect is apparent in intestinal reabsorption of phosphate in Fanconi syndrome.

Acidosis is mainly caused by a defect in the reabsorption of bicarbonate in the proximal tubule. As in all other forms of proximal renal tubular acidosis, the threshold for bicarbonate is low, but distal acidification is normal. Consequently, the urine pH can be lowered appropriately (to a pH of 4.5-5) when the concentration of bicarbonate in plasma is below the threshold. In advanced cases of renal disease, the distal acidifying mechanism is also impaired. Ammoniagenesis appears to be normal.

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