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Managing patients with recurrent renal calculi
The composition of urinary stones may vary from a simple crystal to a complex mixture containing several different species of crystals. The composition of the nidus (center) may be entirely different from that of the peripheral layers.
Eighty percent of patients with kidney stones have a history of recurrent stone formation. Knowledge of stone composition is necessary to guide therapy of patients with recurrent stone formation.
Treatment of urinary calculi is complex.(1) In an overly simplified format, the following patterns are often treated as follows:
-Hyperuricuria and predominately uric acid stones: alkalinize urine to increase uric acid solubility.
-Hypercalciuria and predominately hydroxyapatite stones: acidify urine to increase calcium solubility. However, treatment also depends on urine pH and urine phosphate, sulfate, oxalate, and citrate concentrations.
-Hyperoxaluria and calcium oxalate stones: increase daily fluid intake and consider reduction of daily calcium. However, daily requirements for calcium to maintain good bone formation complicate the treatment.
-Magnesium ammonium phosphate stones (struvite): Investigate and treat urinary tract infection.
See Kidney Stones and Stone Analysis in Publications.
The interpretation of stone analysis results is complex, and beyond the scope of this text. We refer you to chapter 25 of Smith LH: Diseases of the Kidney. Vol 1. Fourth edition. Edited by RW Schrier, CW Gottscholk. Boston, MA, Little, Brown and Company, 1987.
Calcium oxalate stones:
-Production of calcium oxalate stones consisting of oxalate dihydrate indicate that the stone is newly formed and current urine constituents can be used to assess the importance of supersaturation.
-Production of calcium oxalate stones consisting of oxalate monohydrate indicate an old (>2 months since formed) stone and current urine composition may not be meaningful.
Magnesium ammonium phosphate stones (struvite):
-Production of magnesium ammonium phosphate stones (struvite) indicates that the cause of stone formation was infection.
-Treatment of the infection is the only way to inhibit further stone formation.
-Certain herbal and over-the-counter preparations (eg, Mah Jung) contain high levels of ephedrine and guaifenesin. Excessive consumption of these products can lead to the formation of ephedrine/guaifenesin stones.
No significant cautionary statements
1. Lieske JC, Segura JW: Evaluation and medical management of kidney stones. In Essential Urology: A Guide to Clinical Practice. Edited by JM Potts. Totowa, NJ, Humana Press, 2004, pp 117-152
2. Lieske JC: Pathophysiology and evaluation of obstructive uropathy. In Smith's Textbook of Endourology. Second edition. Edited by AD Smith, B Gopal Badlani, D Bagley, et al. Hamilton, Ontario, Canada, BC Decker Inc., 2007, pp 101-106