calcium oxalate stone

75-85% of all renal stones contain calcium. Etiology: 1) hypercalciuria 2) hyperoxaluria a) calcium oxalate b) patients must have an intact colon to absorb oxalate c) free oxalate is increased by free fatty acids competing for Ca⁺² & Mg⁺², usual binders of oxalate d) fatty acid & bile salts increase permeability to oxalate - orlistat inhibits absorption of fatty acids & bile salts & increases risk of hyperoxaluria e) factors increasing hyperoxaluria 1] decreased water absorption 2] decreased bicarbonate absorption 3] decreased absorption of inhibitors f) recessive disorder in oxalate metabolism g) inflammatory bowel disease h) roux-en-Y gastric bypass surgery [5] 3) reduced inhibitor excretion a) Mg⁺² b) pyrophosphates c) citrate 4) primary hyperparathyroidism 5) 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 oxalate stones form in acidic urine Laboratory: 1) serum PTH 2) renal function tests 3) urinalysis & culture - urine microscopy - calcium oxalate 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) reduce intestinal absorption of oxalate a) increase dietary calcium, decrease dietary oxalate & fat may reduce intestinal absorption as oxalate [3,4] b) calcium citrate (Citracal) may be best form [4] c) cholestyramine to bind bile acids (enteric hyperoxaluria) 6) replacement of inhibitor substances a) potassium citrate b) pyrophosphate c) magnesium oxide, magnesium hydroxide, magnesium citrate [7]

General

calcium stone

References

Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 615
Medical Knowledge Self Assessment Program (MKSAP) 11, 16, 17. American College of Physicians, Philadelphia 1998, 2012, 2015
Journal Watch 22(3):20, 2002 Borghi et al, N Engl J Med 346:77, 2002
Prescriber's Letter 9(3):18 2002
Maalouf NM, Tondapu P, Guth ES, Livingston EH, Sakhaee K. Hypocitraturia and hyperoxaluria after Roux-en-Y gastric bypass surgery. J Urol. 2010 Mar;183(3):1026-30. PMID: 20096421
NEJM Knowledge+ Nephrology/Urology
Johansson G, Backman U, Danielson BG et al Effects of magnesium hydroxide in renal stone disease. J Am Coll Nutr. 1982;1(2):179-85 PMID: 6764473

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