Formed when various substances naturally dissolved in urine clump together, for unknown reasons (likely genetic / hereditary). Kidney stones cause pain when they get dislodged from the kidney and flow down the ureter, where they get stuck (see diagram Anatomy of Urinary System).
The pain (often called “Renal Colic) usually begins abruptly, and shoots from the flank to the groin (to the man’s testicle / woman’s labia). There’s usually nausea or vomiting, maybe blood in the urine, but no fever. The abdomen usually is not usually tender to palpation (pressing on it). Fever or tenderness would make us think of Kidney Infection instead, or as a complication of the kidney stone.
The best test to find a kidney stone is a CT scan; an ultrasound usually finds them as well. However, we often make the diagnosis with a simple urinalysis, which shows blood and lots of crystals. We give pain medicine, & other drugs to help the stone pass. We know this by when pain suddenly disappears; on the uncommon occasion it stays stuck more than a day or two, we’d certainly order a CT to determine its size & refer to a Urologist. They have various methods to remove the stone before it causes permanent kidney damage.
We also have patients strain their urine to recover the stone when it passes. If the lab is lucky enough to find the true core (the “nidus”), they can identify the kind of stone. Then if stones happen to recur, there are different medicines to prevent them (depending on what kind they are). If we never find a nidus, we can determine the kind of stone from a 24-hr. urine test (see link for how to collect the specimen, since even many health professionals don’t understand).