Crystal sedimentation and stone formation

Mechanisms of crystal collision being the first step of aggregation (AGN) were analyzed for calcium oxalate monohydrate (COM) directly produced in urine. COM was produced by oxalate titration in urine of seven healthy men, in solutions of urinary macromolecules and in buffered distilled water (control). Crystal formation and sedimentation were followed by a spectrophotometer and analyzed by scanning electron microscopy. Viscosity of urine was measured at 37°C. From results, sedimentation rate (vS), particle diffusion (D) and incidences of collision of particles in suspension by sedimentation (IS) and by diffusion (ID) were calculated. Calculations were related to average volume and urinary transit time of renal collecting ducts (CD) and of renal pelvis. vS was in urine 0.026 ± 0.012, in UMS 0.022 ± 0.01 and in control 0.091 ± 0.02 cm min−1 (mean ± SD). For urine, a D of 9.53 ± 0.97 μm within 1 min can be calculated. At maximal crystal concentration, IS was only 0.12 and ID was 0.48 min−1 cm−3 which, even at an unrealistic permanent and maximal crystalluria, would only correspond to less than one crystal collision/week/CD, whereas to the same tubular wall being in horizontal position 1.3 crystals/min and to a renal stone 624 crystals/cm2 min could drop by sedimentation. Sedimentation to renal tubular or pelvic wall, where crystals can accumulate and meet with a tissue calcification or a stone, is probably essential for stone formation. Since vS mainly depends on particle size, reducing urinary supersaturation and crystal growth by dietary oxalate restriction seems to be an important measure to prevent aggregation

Management of urolithiasis in pregnancy

Michelle Jo Semins,1 Brian R Matlaga21University of Pittsburgh Medical Center, Pittsburgh, PA, USA; 2Johns Hopkins Medical Institutions, Baltimore, MD, USAAbstract: Kidney stones are very common and unfortunately do not spare the pregnant population. Anatomical and pathophysiological changes occur in the pregnant female that alter the risk for development of nephrolithiasis. Acute renal colic during pregnancy is associated with significant potential risks to both mother and fetus. Diagnosis is often challenging because good imaging options without radiation use are limited. Management of diagnosed nephrolithiasis is unique in the pregnant population and requires multi-disciplinary care. Herein, we review the metabolic alterations during pregnancy that may promote kidney stone formation, the complications associated with acute renal colic in the pregnant state, and our proposed diagnostic and management algorithms when dealing with this clinical scenario.Keywords: kidney stones, nephrolithiasis, pregnanc