Urinary excretion of excess sulfurous amino acids (e.g., cysteine and methionine), uric acid, and other acidic metabolites from animal protein acidifies the urine, which promotes the formation of kidney stones. Low urinary-citrate excretion is also commonly found in those with a high dietary intake of animal protein, whereas vegetarians tend to have higher levels of citrate excretion. Low urinary citrate, too, promotes stone formation. Vitamins
The evidence linking vitamin C supplements with an increased rate of kidney stones is inconclusive. The excess dietary intake of vitamin C might increase the risk of calcium-oxalate stone formation. The link between vitamin D intake and kidney stones is also tenuous. Excessive vitamin D supplementation may increase the risk of stone formation by increasing the intestinal absorption of calcium; correction of a deficiency does not. Pathophysiology
Supersaturation of urine
When the urine becomes supersaturated (when the urine solvent contains more solutes than it can hold in solution) with one or more calculogenic (crystal-forming) substances, a seed crystal may form through the process of nucleation. Heterogeneous nucleation (where there is a solid surface present on which a crystal can grow) proceeds more rapidly than homogeneous nucleation (where a crystal must grow in a liquid medium with no such surface), because it requires less energy. Adhering to cells on the surface of a renal papilla, a seed crystal can grow and aggregate into an organized mass.
A CT scan is also not typically recommended in children.Otherwise a noncontrast helical CT scan with 5 millimeters (0.2 in) sections is the diagnostic method to use to detect kidney stones and confirm the diagnosis of kidney stone disease. Near all stones are detectable on CT scans with the exception of those composed of certain drug residues in the urine, such as from indinavir. Where a CT scan is unavailable, an intravenous pyelogram may be performed to help confirm the diagnosis of urolithiasis. This involves intravenous injection of a contrast agent followed by a KUB film. Uroliths present in the kidneys, ureters, or bladder may be better defined by the use of this contrast agent. Stones can also be detected by a retrograde pyelogram, where a similar contrast agent is injected directly into the distal ostium of the ureter (where the ureter terminates as it enters the bladder).Renal ultrasonography can sometimes be useful, because it gives details about the presence of hydronephrosis, suggesting that the stone is blocking the outflow of urine. Radiolucent stones, which do not appear on KUB, may show up on ultrasound imaging studies. Other advantages of renal ultrasonography include its low cost and absence of radiation exposure. Ultrasound imaging is useful for detecting stones in situations where X-rays or CT scans are discouraged, such as in children or pregnant women. Despite these advantages, renal ultrasonography in 2009 was not considered a substitute for noncontrast helical CT scan in the initial diagnostic evaluation of urolithiasis.