Urinary pH and renal lithiasis

Abstract

Formation of calcium oxalate crystals, either as monohydrate or dihydrate, is apparently unrelated to urinary pH because the solubilities of these salts are practically unaltered at physiologic urinary pH values. However, a urinary pH <5.5 or >6.0 may induce uric acid or calcium phosphate crystals formation, respectively, which under appropriate conditions may induce the development of the calcium oxalate calculi. We assessed the relationship between the urinary pH and the formation of different types of calculi. A retrospective study in 1,478 patients was done. We determined the composition, macrostructure, and microstructure of the calculi and the urinary pH, 50.9% of calcium oxalate monohydrate unattached calculi were present in patients with urinary pH <5.5. We found that 34.1 and 41.5% of calcium oxalate dihydrate calculi were present in patients with urinary pH <5.5 and >6.0, respectively. Infectious calculi were found primarily in patients with urinary pH >6.0 (50.7%). Only calcium oxalate monohydrate papillary calculi were associated with urinary pH between 5.5 and 6.0 (43.1%). Urine of pH <5.5 shows an increased capacity to develop uric acid crystals, which can act as a heterogeneous nuclei of calcium oxalate crystals. In contrast, urine of pH >6.0 has an increased capacity to develop calcium phosphate crystals, which can act as a heterogeneous nuclei of calcium oxalate crystals. Oxalate monohydrate papillary calculi were associated to pH between 5.5 and 6.0 because the injured papilla acts as a heterogeneous nucleant. Consequently, measurement of urinary pH may be used to evaluate the lithogen risk of given urine.

Relationship between Components of urinary crystallites and Formation of Calcium Oxalate Stones---An Investigation of 275 Cases of Patients with Calcium Oxalate Stones

“…In urine with pH < 5.5, the solubility of UA significantly decreases and the precipitated UA crystals can function in heterogeneous nucleation to induce the formation of CaOx stone; as a result, COM/UA stone is produced [15].…”

Nanouric acid or nanocalcium phosphate as central nidus to induce calcium oxalate stone formation: a high-resolution transmission electron microscopy study on urinary nanocrystallites

“…15,38,39 All of them can function as nidus to induce the development of COM calculi. 40 The main components in the interior layer of CaOx stones were CaOx and CaP, whereas in the surrounding region it was CaOx. 41 Thus, CaP induced the development of COM calculi through heterogeneous nucleation, which has been evidenced by this paper in nanoscale.…”

“…33 However, at urine pH 5.5, anhydrous UA or dihydrate UA crystals will precipitate, and these crystals can act as heterogeneous nucleating agents that induce the formation of COM-UA mixed stones. 40 A slight imbalance and change in urine pH can result in the rapid growth of amorphous calcium phosphate, 49 and at urine pH 6.0, CaP crystals can precipitate; these can lead to the formation of mixed CaOx-CaP stones. 16 …”

Structure and Composition of Non-Infectious Phosphate Calculi Formed in Patients with Low and High Urinary Phosphate Concentrations

“…All stones containing calcium phosphate form in urine at higher pH [3][4][5][6]. In addition, hypercalciuria and hyperphosphaturia are often associated with phosphate stones [4,7].…”