Abstract
Uric acid crystallizes as an anhydrous compound (UAA), a dihydrate (UAD) or a mixture of both. A monohydrate form is very rare. About 20% of uric acid stones contain a significant amount (≥20%) UAD. It is believed that UAD crystallizes under highly acidic conditions (urine pH ≤ 5.0). Up to now, metabolic data on patients with UAD stones have not been reported in the literature. One hundred and fifty patients with pure uric acid calculi were studied. Stone analysis was performed using X-ray diffraction. According to the stone analysis, they were divided in two groups: 1. UAD (≥20% UAD), 2. UAA (<20% UAD). In all patients the following parameters were examined: age, sex, number of recurrences, body mass index (BMI); blood: creatinine, uric acid, calcium, sodium, and potassium; urine: pH-profiles, volume, calcium, uric acid, citrate, ammonia, and urea. Group 1 (≥20% UAD) consisted of33patientsand group 2 (<20% UAD) of 117 patients. Between these groups, there was a significant difference concerning the number of recurrences, the urine volume, and the urinary excretion of calcium. Patients with ≥20% dihydrate had a mean BMI of 31.6 ± 7.5, a mean number of recurrences of 0.24 ± 0.44, an urine volume of 2.6 ± 0.8 l/24 h, and a calcium excretion of 4.5 ± 2.2 mmol/24 h, whereas those with <20% dihydrate had BMI of 29.9 ± 5.0, 1.10 ± 1.42 recurrences, urine volume of 2.3 ± 1.2 l/24 h, and calcium excretion of 3.2 ± 2.4 mmol/24 h. All the other parameters tested were not significantly different. For the first time, our study shows metabolic data in uric acid patients with a significant amount of UAD. The comparison between this group and those patients with <20% UAD revealed that the first group is less prone to develop recurrences. This is a relevant difference concerning the necessity of metaphylactic measures. We could not confirm in patients with dihydrate if the urinary pH is more acid than in those with insignificant amounts of dihydrate. The higher 24-h urine volume, the higher excretion of calcium, and the higher BMI in the UAD group may be of pathophysiological relevance and requires further attention.
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References
Abate N, Chandalia M, Cabo-Chan AV Jr, Moe OW, Sakhaee K (2004) The metabolic syndrome and uric acid nephrolithiasis: novel features of renal manifestation of insulin resistance. Kidney Int 65:386–392
Borghi L, Meschi T, Amato F, Briganti A, Novarini A, Giannini A (1996) Urinary volume, water and recurrences in idiopathic calcium nephrolithiasis: a 5-year randomized prospective study. J Urol 155:839–843
Borghi L, Meschi T, Schianchi T, Briganti A, Guerra A, Allegri F, Novarini A (1999) Urine volume: stone risk factor and preventive measure. Nephron 81(1):31–37
Börner RH, Schneider HJ, Berg W (1981) Stabilizing factors for uric acid dihydrate—contribution to uric acid stone formation. In: Smith LH, Robertson WG, Finlayson B (eds) Urolithiasis. Plenum Press, New York, pp 465–469
Daudon M, Lacour B, Jungers P (2005) High prevalence of uric acid calculi in diabetic stone formers. Nephrol Dial Transpl 20:468–469
Grases F, Villacampa AI, Costa-Bauza A, Sohnel O (2000) Uric acid calculi: types, etiology and mechanisms of formation. Clin Chim Acta 302:89–104
Hesse A, Bach D (1982) Harnsteine—Pathobiochemie und klinisch-chemische Diagnostik. Stuttgart
Hesse A, Schneider HJ, Berg W, Hienzsch E (1975) Uric acid dihydrate as urinary calculus component. Invest Urol 12:405–409
Schubert G, Reck G, Jancke H, Kraus W, Patzelt C (2005) Uric acid monohydrate—a new urinary calculus phase. Urol Res 33:231–238
Strohmaier WL, Hoelz KJ, Bichler KH (1997) Spot urine samples for the metabolic evaluation of urolithiasis patients. Eur Urol 32:294–300
Strohmaier WL, Seilnacht J, Schubert G (2009) Parameters of metabolic syndrome in uric acid and calcium oxalate stone formers. Arch Ital Urol Androl 81:152–153
Strohmaier WL, Weigl A (1997) Stone composition in Upper Franconia—unusually high percentage of uric acid lithiasis. In: Jungers P, Daudon M (eds) Renal stone disease. Elsevier Science, Amsterdam, pp 10–11
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Strohmaier, W.L., Seilnacht, J. & Schubert, G. Clinical significance of uric acid dihydrate in urinary stones. Urol Res 39, 357–360 (2011). https://doi.org/10.1007/s00240-010-0356-4
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DOI: https://doi.org/10.1007/s00240-010-0356-4