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Common Urological Problems

Urinary Ions

  • - General Urology - Common Urological Problems - Urinary Stone Disease
  • Jul 25, 2010
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Tags: | calcium | chronic diarrhea | citrate | dietary magnesium |

Although not identified as one of the major constituents of most urinary calculi,  sodium plays an important role in regulating the crystallization of calcium salts in urine.

Sodium is found in higher than expected concentrations in the core of renal calculi and may play a role in initiating crystal development and aggregation. High dietary sodium intake increases urinary calcium excretion. This reduces the ability of urine to inhibit calcium oxalate crystal agglomeration.  These effects are thought to be due to a sodium-induced increase in bicarbonaturia and decrease in serum bicarbonate.  Conversely,  a reduction in dietary sodium helps to reduce recurrent calcium nephrolithiasis.

image Figure 16–2.  Radiolucent right staghorn renal calculus appreciated after percutaneous injection of radiocontrast material. This uric acid stone was effectively removed in a single percutaneous procedure. Postoperative urinary alkalinization has been effective prophylaxis.

Citrate is a key factor affecting the development of calcium urinary stones. A deficiency commonly is associated with stone formation in those with chronic diarrhea or renal tubular acidosis type I (distal tubular defect) and in patients undergoing chronic thiazide therapy.  Citrate plays a pivotal role in the citric acid cycle in renal cells.

Metabolic stimuli that consume this product (as with intracellular metabolic acidosis due to fasting, hypokalemia, or hypomagnesemia) reduce the urinary excretion of citrate. Estrogen increases citrate excretion and may be a factor that decreases the incidence of stones in women, especially during pregnancy. Alkalosis also increases citrate excretion.

Urinary Stone Disease

Urinary Stone Disease

Dietary magnesium deficiency is associated with an increased incidence of urinary stone disease. Magnesium is a component of struvite calculi.  Experimentally,  lack of dietary magnesium is associated with increased calcium oxalate stone formation and calcium oxalate crystalluria.

The exact mechanism whereby magnesium exerts its effect is undefined. Dietary magnesium supplements do not protect against stone formation in normal people.

Urinary sulfates may help prevent urinary calculi.  They can complex with calcium. These sulfates occur primarily as components of longer urinary proteins,  such as chondroitin sulfate and heparin sulfate.

Inhibitors of urinary stone formation other than citrate, magnesium, and sulfates have been identified. These consist predominantly of urinary proteins and other macromolecules such as glycosaminoglycans,  pyrophosphates, and uropontin.  Although citrate appears to be the most active inhibitory component in urine,  these substances demonstrate a substantial role in preventing urine crystal formation. The N–terminal amino acid sequence and the acidic amino acid content of these protein inhibitors, especially their high aspartic acid content, appear to play pivotal inhibitory roles. Fluoride may be an inhibitor of urinary stone formation.


Marshall L. Stoller, MD


  1. Ackermann D et al: Influence of calcium content in mineral water on chemistry and crystallization conditions in urine of calcium stone formers. Eur Urol 1988;14:305.
  2. Allie-Hamdulay S et al: Prophylactic and therapeutic properties of a sodium citrate preparation in the management of calcium oxalate urolithiasis:  Randomized,  placebo-controlled trial.  Urol Res 2005;33:116.
  3. Bilezikian JP et al:  Primary hyperparathyroidism:  New concepts in clinical,  densitometric and biochemical features.  J Intern Med 2005;257:6.
  4. Fellstrom B et al: Dietary habits in renal stone patients compared with healthy subjects. Br J Urol 1989;63:575.
  5. Gentle DL et al: Geriatric nephrolithiasis. J Urol 1997;158:2221.
  6. Heller HJ et al: Effect of dietary calcium on stone forming propensity. J Urol 2003;169:470.
  7. Langley SE, Fry CH: The influence of pH on urinary ionized [Ca2+]:

Full References  »


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