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calcium phosphate stone

75-85% of all renal stones contain calcium. Etiology: 1) hypercalciuria - renal tubular acidosis (RTA) type 1 (calcium phosphate) - topiramate 2) reduced inhibitor excretion a) Mg+2 b) pyrophosphates c) citrate (RTA-1)4) primary hyperparathyroidism 3) primary hyperparathyroidism 4) sarcoidosis Epidemiology: - most common in 3rd to 5th decade of life Pathology: 1) 1,25-dihydroxyvitamin D3 levels may be increased 2) inappropriate calciuria may occur with calcium-restricted diets 3) calcium phosphate stones form in alkaline urine 4) urinary citrate diminishes with increased urinary pH - carbonic anhydrase inhibitors (topiramate) increase bicarbonate excreted into the urine & thus urinary pH Laboratory: 1) serum PTH 2) renal function tests 3) urinalysis & culture - urine microscopy - calcium phosphate crystals in urine 4) 24 hour urine: a) hypercalciuria: > 300 mg (men) or 250 mg (women) or > 4 mg/kg in 24 hours b) creatinine c) uric acid 5) 24 hour urine volume 6) serum Ca+2 is generally normal 7) stone analysis Management: 1) correcting dietary stresses a) Na+ increases urinary Ca+2 -> diet of < 3 g of salt/day [4] b) animal protein increases urinary Ca+2 -> diet of < 8 oz of meat/day [4] 2) increasing urine volume > 2.5L/day 3) thiazide diuretics for hypercalciuria a) Na+ must be restricted for urine Ca+2 to decrease by 50% b) development of hypercalcemia suggests latent hyperparathyroidism c) amiloride may also be of benefit 4) patients with primary hyperparathyroidism & urolithiasis - removal of parathyroid adenoma 5) replacement of inhibitor substances a) potassium citrate b) pyrophosphate c) magnesium oxide

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calcium phosphate crystals in urine

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calcium stone

References

  1. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 615
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 16, 17. American College of Physicians, Philadelphia 1998, 2012, 2015
  3. Journal Watch 22(3):20, 2002 Borghi et al, N Engl J Med 346:77, 2002
  4. Prescriber's Letter 9(3):18 2002
  5. NEJM Knowledge+ Nephrology/Urology