Kidney Stones: Diagnosis
The best available test is a CAT scan of the abdomen and pelvis. Almost all stones appear very white on a non-contrast CAT scan, so they are generally easy to find when they overlie the grey areas of the kidneys or ureters. The CAT scan also allows the doctors to take measurements on stone size, location, and density – all of which helps guide the decision about how to best manage the stone.
An IVP (intravenous pyelogram) is another test that can diagnose most stones. It is less commonly used nowadays because it does not have the precision of a CAT scan, and it involves the injection of intravenous contrast to “light up” the kidneys. People with poor kidney function cannot have IV contrast. A small percentage of people may have a serious reaction to contrast, so the IVP is less commonly done today.
A renal ultrasound might show a kidney stone and kidney obstruction, but the ultrasound can miss a ureteral stone. A plain X-ray of the abdomen (called a “KUB”, short for kidneys, ureters, and bladder film) can show larger stones, but it will often miss small stones. A KUB is unreliable for diagnosis of uric acid and cystine stones.
The urinalysis may show blood in the urine and occasionally the presence of an infection. Blood work may show impairment of kidney function.