Study of the Factors That Affect the Regrowth of Calcium Oxalate Dihydrate Fragmented Calculi

Background: The application of extracorporeal shock wave lithotripsy (ESWL) to calcium oxalate dihydrate (COD) renal calculi gives excellent fragmentation results. Nevertheless, the retention of postESWL fragments within the kidney is still an important trouble. The aim of this paper is to study the regrowth of COD real spontaneously passed post-ESWL calculi fragments as a function of urinary conditions and crystallization inhibitors. Methods: An “in vitro” system with synthetic urine was used to study the regrowth of post-ESWL fragments of COD calculi. Fragments growth was evaluated through their weight increase. The growth of the different fragments was uniformized by using the relative mass increase. Results: In all the studied conditions the COD renal calculi fragments exhibited an important capacity to induce the growth of calcium oxalate monohydrate (COM) crystals on COD crystal faces. At urinary pH = 5.5 and normocalciuria only COM crystals were formed (growth rate = 0.22 ± 0.04 μg/mg h). At urinary pH = 5.5 and hypercalciuria COM crystals and very few new COD crystals were detected (growth rate = 0.32 ± 0.03 μg/mg h). At urinary pH = 6.5 and normocalciuria only COM and few new COD crystals were detected (growth rate = 0.35 ± 0.05 μg/mg h). At urinary pH = 6.5 and hypercalciuria large amounts of COD, COM, hydroxyapatite and brushite crystals were seen (growth rate = 3.87 ± 0. 34 μg/mg h). A study of three crystallization inhibitors demonstrates that phytate attained a total inhibition of COD calculi fragments growth (2.27 μM at pH = 5.5 and 4.55 μM at pH = 6.5, both cases with hypercalciuria). 69.0 μM of pyrophosphate accomplished a reduction of 87% in the mass increase of the calculi fragments (at pH = 6.5 and hypercalciuria). Citrate (5.29 mM) did not cause any significant inhibition of COD calculi fragments mass increase at pH = 6.5 and hypercalciuria. Conclusion: The growth rate of COD calculi fragments was similar in all conditions except made at pH = 6.5 and hypercalciuria, in which case the growth rate was approximately ten times superior. This demonstrates the important risk factor that could imply the presence of COD calculi residual fragments in the kidneys together with hypercalciuria and high urinary pH values. Nevertheless, crystallization inhibitors can notably slow down the calculi fragments development.