Urinary saturation and risk factors for calcium oxalate stone disease based on spot and 24-hour urine specimens

Abstract

In 222 random spot urine specimens, the calcium concentration and calcium oxalate saturation [DG(CaOx)] were significantly higher among stone formers than among non-stone formers, while the citrate and creatinine-corrected citrate concentrations were lower. In 188 24-hour urine specimens, magnesium excretion was lower among stone formers than non-stone formers, while the creatinine-corrected calcium concentration and DG(CaOx) were higher. Among stone formers, there was no gender difference in the urinary concentrations of calcium, oxalate, citrate, magnesium, and DG(CaOx), but the creatinine-corrected calcium, citrate, and magnesium concentrations were higher in women, as well as 24-hour citrate excretion. The levels of calcium and oxalate have a major influence on DG(CaOx), while citrate and magnesium levels have a minor influence. DG(CaOx) was correlated with calcium and oxalate excretion, as well as with the creatinine-corrected calcium and oxalate concentrations. Approximately 5% of 24-hour urine specimens showed critical supersaturation, 80% showed metastable supersaturation, and 15% were unsaturated. Hypercalciuria or hyperoxaluria was fairly common (30% and 40%) in critically supersaturated urine, while it was less common (22.4% and 8.6%) in metastably supersaturated urine and was not detected in unsaturated urine. Hypocitraturia and/or hypomagnesiuria was more common (63.8-80%) at any saturation. The urinary calcium, oxalate, and citrate concentrations, as well as the creatinine-corrected calcium, oxalate, citrate, and magnesium concentrations and DG(CaOx), showed a significant correlation between 57 paired early morning spot urine and 24-hour urine specimens. The creatinine-corrected calcium and citrate concentrations of the early morning urine specimens were significantly correlated with the levels of calcium and citrate excretion in the paired 24-hour urine specimens. In conclusion, no parameter other than urinary saturation gives more than a vague indication of the risk of lithogenesis, so DG(CaOx) in either early morning urine or 24-hour urine specimens appears to be the best predictor of stone risk. Finally, the creatinine-corrected calcium and citrate concentrations in early morning urine can be used as a substitute for measuring 24-hour excretion.

Associations between renal sodium‐citrate cotransporter (hNaDC‐1) gene polymorphism and urinary citrate excretion in recurrent renal calcium stone formers and normal controls

“…demonstrated that 24‐h urinary citrate excretion was not positively associated with calcium oxalate supersaturation (DG[CaOx]). In contrast, hypercalciuria or hyperoxaluria was fairly common in critically supersaturated urine 25 . They concluded that hypocitraturia alone is not a good predictor of urinary calcium oxalate supersaturation, but it may be associated with the underlying etiological condition.…”

Assessment of crystallization risk formulas in pediatric calcium stone-formers

“…Although with some exceptions, patients with calcium urolithiasis generally excrete more lithogenic (calcium, oxalate) and less stone-inhibitory substances (citrate, magnesium) in urine than healthy individuals, no single urinary parameter is able to discriminate these two groups sufficiently [6,10,22,23], partially because stoneformers constitute an extremely heterogeneous group with respect to urolithiasis etiology. In terms of metabolic factors, typical lithogenic abnormalities, such as hypercalciuria, hyperoxaluria, or hypocitraturia, occur in different proportions and only in a portion of all patients.…”

Stress–stones–stress–recurrent stones: a self-propagating cycle? Difficulties in solving this dichotomy

“…This has proved to be successful as creatinine-corrected calcium and citrate concentrations in early morning urine have been shown to be a substitute for 24-h excretion of these analytes [25]. However, the creatinine ratios for Ox, Mg and UA are not accurate predictors of 24-h excretions [25] but are nevertheless widely used for standardizing concentrations in non-24-h urine collections. Accordingly, urine concentrations were adjusted against creatinine by computing the ratios Ca/Cr, Ox/Cr, Mg/Cr, Cit/Cr and urate/Cr.…”

“…Since spot urine concentrations are known to be highly dependent on fluid intake, such measurements are adjusted for creatinine owing to its relatively constant excretion throughout the day, and within and across populations [24]. This has proved to be successful as creatinine-corrected calcium and citrate concentrations in early morning urine have been shown to be a substitute for 24-h excretion of these analytes [25]. However, the creatinine ratios for Ox, Mg and UA are not accurate predictors of 24-h excretions [25] but are nevertheless widely used for standardizing concentrations in non-24-h urine collections.…”