Cystinuria: clinical practice recommendation

Abstract

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The Impact of Diet on Urinary Risk Factors for Cystine Stone Formation

“…The present study, with normal subjects, was not able to confirm the previous findings, and thus rejected the hypothesis of an effect of dietary sodium intake, as judged by urinary excretion, on urinary cystine excretion. Although no association between dietary sodium intake and urinary cystine excretion was observed in the present study, restricting dietary sodium to 2300 mg/day (100 mmol/day) or 6 g/day of sodium chloride is recommended as part of a healthy diet, even if its potential benefit in preventing cystine stones is not supported by clinical trials [11]. Strict dietary sodium restriction to below 2 g per day is not necessary, and is difficult to achieve and maintain.…”

“…The mechanism that determines the association of increased urinary cystine excretion with increased sodium intake in cystinuric patients is unknown, as the reabsorption of cystine in the proximal tubule is sodium-independent [17,36,37]. It was speculated that high sodium intake would increase the intracellular neutral amino acid and sodium load, which might slow the apical reabsorption of cystine [11,36,37]. The present study, with normal subjects, was not able to confirm the previous findings, and thus rejected the hypothesis of an effect of dietary sodium intake, as judged by urinary excretion, on urinary cystine excretion.…”

“…The upper limit of solubility of cystine at a physiological urine pH range between 5 and 7 is approximately 300-400 mg/L (1.3-1.7 mmol/L), but cystine solubility increases markedly when urine pH is raised to above 7.5 [26]. Urine alkalinization to reach the therapeutic target of pH 7.5 to 8.0 is a cornerstone of treatment of all patients with cystinuria and is recommended as a basic measure [10,11]. However, large doses of alkalizing agents are required to achieve the recommended urine pH range and gastrointestinal side effects can limit compliance with treatment [38][39][40].…”

“…To maintain cystine concentration below the solubility limit of 1.3 mmol/L (300 mg/L) at pH 6 in adult patients with cystinuria, urine volume of at least 3.0 L per 24 h should be achieved [9,11,25,[41][42][43][44]. To ensure adequate hydration, a urine specific gravity of less than 1.005 has been recommended [11,45]. Hydration has been found to prevent recurrent stone formation in as many as two-thirds of patients with cystinuria [46].…”

“…Dietary treatment plays a pivotal role in the management of cystine stone formation. The primary treatment strategy for cystine stone disease is focused on reducing 24 h urinary cystine excretion and concentration and increasing urinary cystine solubility [9][10][11]. High fluid intake to decrease urinary cystine concentration is the most important measure to prevent recurrences in patients with cystinuria.…”