Kidney stones (ureterolithiasis) result from stones or renal calculi in the ureter. The stones are solid concretions or calculi (crystal aggregations) formed in the kidneys from dissolved urinary minerals. Nephrolithiasis refers to the condition of having kidney stones. Urolithiasis refers to the condition of having calculi in the urinary tract (which also includes the kidneys), which may form or pass into the urinary bladder. Ureterolithiasis is the condition of having a calculus in the ureter, the tube connecting the kidneys and the bladder. The term bladder stones usually applies to urolithiasis of the bladder in non-human animals such as dogs and cats.
Clinical diagnosis is usually made on the basis of the location and severity of the pain, which is typically colicky in nature (comes and goes in spasmodic waves). Pain in the back occurs when calculi produce an obstruction in the kidney.
Imaging is used to confirm the diagnosis and a number of other tests can be undertaken to help establish both the possible cause and consequences of the stone.
The relatively dense calcium renders these stones radio-opaque and they can be detected by a traditional X-ray of the abdomen that includes the kidneys, ureters and bladder—KUB. This may be followed by an IVP (intravenous pyelogram—intravenous urogram (IVU) is the same test by another name) which requires about 50 ml of a special dye to be injected into the bloodstream that is excreted by the kidneys and by its density helps outline any stone on a repeated X-ray. These can also be detected by a retrograde pyelogram where similar “dye” is injected directly into the ureteral opening in the bladder by a surgeon, usually a urologist.
About 10% of stones do not have enough calcium to be seen on standard X-rays (radiolucent stones).
Computed tomography without contrast is considered the gold standard diagnostic test for the detection of kidney stones. All stones are detectable by CT except very rare stones composed of certain drug residues in the urine. If positive for stones, a single standard X-ray of the abdomen (KUB) is recommended. This gives a clearer idea of the exact size and shape of the stone as well as its surgical orientation. Further, it makes it simple to follow the progress of the stone by doing another X-ray in the future.
Drawbacks of CT scans include radiation exposure and cost.
Ultrasound imaging is useful as it gives details about the presence of hydronephrosis (swelling of the kidney—suggesting the stone is blocking the outflow of urine). It can also be used to detect stones during pregnancy when x-rays or CT are discouraged. Radiolucent stones may show up on ultrasound however they are also typically seen on CT scans.
Some recommend that US be used as the primary diagnostic technique with CT being reserved for those with negative US result and continued suspicion of a kidney stone. This is due to its lesser cost and avoidance of radiation.
Other investigations typically carried out include:
Microscopic study of urine, which may show proteins, red blood cells, bacteria, cellular casts and crystals.
Culture of a urine sample to exclude urine infection (either as a differential cause of the patient’s pain, or secondary to the presence of a stone).
Blood tests: Full blood count for the presence of a raised white cell count (Neutrophilia) suggestive of infection, a check of renal function and to look for abnormally high blood calcium blood levels (hypercalcaemia).
24 hour urine collection to measure total daily urinary volume, magnesium, sodium, uric acid, calcium, citrate, oxalate and phosphate.
Catching of passed stones at home (usually by urinating through a tea strainer or stonescreen) for later examination and evaluation by a doctor.
Bilateral kidney stones on abdominal X-ray. Not to be confused with phleboliths seen in the pelvis.
Star-shaped bladder urolith on an X-ray of the pelvis.
CT of abdomen without contrast showing right proximal ureteric stone causing mild obstruction and hydronephrosis (marked by an arrow).
Three-dimensional reconstructed CT scan image of a ureteral stent in the left kidney (indicated by yellow arrow). There is a kidney stone in the pyelum of the lower pole of the kidney (highest red arrow) and one in the ureter beside the stent (lower red arrow).