The leading cause of kidney stones is a lack of water in the body. Kidney stones form when your urine contains more crystal-forming substances — such as calcium, oxalate and uric acid — than the fluid in your urine can dilute. At the same time, your urine may lack substances that prevent crystals from sticking together, creating an ideal environment for kidney stones to form.
They take an average of 31 days to pass. Stones that are 4–6 mm are more likely to require some sort of treatment, but around 60 percent pass naturally. This takes an average of 45 days. Stones larger than 6 mm usually need medical treatment to be removed.
Diagnosis of kidney stones is best accomplished using an ultrasound, intravenous pyelography (IVP), or a CT scan. Most kidney stones will pass through the ureter to the bladder on their own with time. Treatment includes pain-control medications and, in some cases, medications to facilitate the passage of urine.