RISK STRATIFICATION The risk of stone recurrence is 14% at 1 year,35% at 2 years and 52% at 10 years after asingle episode.Uribarri J, Oh MS and Carroll HJ: The first kidney stone. Ann Intern Med 1989; 111: 1006.
Simplified evaluation first time stone former with no remaining stones(low risk) Comprehensive approach patients who are recurrent or first time stoneformers who have medical conditions associatedwith stone formation. Such as gout, bowel disease, bone disease,morbid obesity, metabolic syndrome, primaryhyperparathyroidism and type 1 renal tubularacidosis
DIAGNOSTIC EVALUATION History Frequency of stone events Prior stone removing interventions Underlying diseases (bowel disease, gout,primary hyperparathyroidism…) Medication (Furosamide, Alkalizing agent…) Diet history Stone analysis recommended in recurrent stone formers even ifthe initial stone composition is known
X-ray powder diffraction crystallography semiquantitative analysis, relative amounts of thestone components are generated Fourier transform infrared spectroscopy Reported the relative percentage of stonecomponents Serum chemistry studies electrolytes, blood urea nitrogen, creatinine,calcium and uric acid
Simplified approach history stone analysis serum chemistry studies Comprehensive approach Add 24-hour urine testing The collection of 2, 24-hour urine specimens isrecommended
24-hour urine testing Urine volume Creatinine, calcium, oxalate, citrate, uric acid,sodium, potassium, magnesium, phosphate,ammonia, urea nitrogen, sulfate, pH Creatinine should be 18 to 24 mg/kg daily formales and 15 to 20 mg/kg daily for females Spot urine testing has been advocated bysome for convenience
Stone forming salts index EQUIL analysis 13 ions Tiselius index major contributors to supersaturation of calciumsalts simpler to use Bonn stone index Simplest, estimate calcium oxalate risk JESS (joint expert speciation system)
DIETARY THERAPY Increasing fluid consumption has beendemonstrated to reduce stone recurrence in firsttime calcium oxalate stone formers Group 1 (99 patients) was instructed to consumeenough water to maintain a urine volume of at least 2la day. Group 2 (100 patients) did not. Urine volumes of group 1 significantly increased, andthe relative supersaturation of calcium oxalate,calcium phosphate and uric acid significantlydecreased from baseline levels. This status was maintained during the 5 year followup period.Borghi L, Meschi T, Amato F et al: Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis:a 5-year randomized prospective study. J Urol 1996; 155: 839.
Stone recurrence was higher in those who hadlower urine volumes. Water type: Urinary citrate excretion andcalcium excretion were highest during highcalcium and bicarbonate contents waterconsumption while oxalate excretion waslowest.Di Silverio F, Ricciuti GP, D’Angelo AR et al: Stone recurrence after lithotripsy in patients with recurrent idiopathic calcium urolithiasis:efficacy of treatment with fiuggi water. Eur Urol 2000; 37: 145.Caudarella R, Rizzoli E, Buffa A et al: Comparative study of the influence of 3 types of mineral water in patientswith idiopathic calcium lithiasis. J Urol 1998; 159: 658.
Reduced dietary calcium consumption, andincreased oxalate and fructose intake havebeen identified as risk factors for developing akidney stone. reduced calcium consumption has been attributedto increased oxalate absorption and renalexcretion Increased oxalate consumption increases itsurinary excretionHolmes RP, Goodman HO and Assimos DG: Contribution of dietary oxalate to urinary oxalate excretion. Kidney Int 2001; 59: 270.
At 5 years the relative risk of kidney stonerecurrence on the normal calcium was half thatof the low calcium diet. Protein restriction may not benefit all calciumstone formers.
All calcium stone formers should consumewell-balanced meals such as those proposedin the DASH strategy. limit animal protein (<50 gm a day) sodium intake (<100 mEq or 2.3 gm a day) maintaining adequate dietary calcium intake (1 to1.2 gm a day for adults)
Controlling calcium excretion Patients with urinary calcium excretion belowthe threshold of hypercalciuria may benefitfrom such intervention. Thiazide therapy resulted in a statisticallysignificant reduction (21.3%) in stonerecurrence compared to no treatment orplacebo. (Level 1) Thiazide therapy resulted in a 61% reductionin stone recurrence and an 18% decrease instone formation rate.
Thiazide diuretics inhibit sodium reabsorptionin the distal convoluted tubule, promotingsodium and water loss. Resulting in volume contraction whichpromotes passive reabsorption (30-50%) ofcalcium in the proximal tubule leading to itsdiminished urinary excretion.
Thiazides can induce hypokalemia andhypocitraturia. It may be necessary to prescribe potassiumcitrate or potassium chloride adjunctively toprevent hypokalemia, intracellular acidosis andresultant hypocitraturia.
Augmenting citrate excretion Hypocitraturia has several etiologies includingdistal RTA, bowel disturbances and use ofthiazide diuretics. Potassium citrate increases urine pH andurinary citrate excretion, improves metabolicacidosis and inhibits precipitation of calciumoxalate crystals.
Sodium citrate or sodium bicarbonate is usedin patients who do not tolerate the potassiumpreparation. A disadvantage of these agents is the increasein calcium excretion.
Controlling uric acid excretion Allopurinol is a xanthine oxidase inhibitor thatblocks conversion of hypoxanthine to xanthine,a uric acid precursor. Allopurinol significantly decreased the rate ofstone recurrence as well as significantlyprolonged the interval to stone recurrence. Febuxostat is a relatively new inhibitor with alower risk.
Augmenting magnesium excretion Magnesium increases the solubility of calcium,oxalate and phosphate in the urine. 500 mg bid magnesium oxide or magnesiumgluconate orally with meals for adults benefits. A common side effect of magnesiumsupplementation is diarrhea.
Controlling oxalate excretion The majority of patients have idiopathichyperoxaluria. The typical adult dose of pyridoxine therapy is50 to 100 mg daily, and neurotoxicity is apotential side effect. Primary hyperoxaluria should be suspected inany adult with a daily oxalate excretion >75 mg.
Primary hyperparathyroidism High normal serum calcium level and aninappropriately high normal or increasedparathyroid hormone level. Removal of the offending parathyroid gland willusually dramatically attenuate stone activity. Secondary hyperparathyroidism such as renalhypercalciuria and vitamin D deficiency shouldbe ruled out.
ECONOMICS The fiscal encumbrance associated with stonedisease is not simply limited to the associatedmedical costs, but also incorporates lost. The cost-effectiveness of medical therapy forpreventing in idiopathic calcium stone formershas been provided, estimated a $1,162 to$3,162 savings, which was assuming an 83%rate of remission.
The cost-effectiveness of medical therapy forrecurrent nephrolithiasis will vary from patientto patient, hinging on certain factors such asfrequency of repeat stone events, patientcompliance with therapy and efficacy oftherapy.