History and Physical Examination
Initial evaluation of a individual suspected of having a kidney stone consists of a complete history and physical examination. The symptoms of renal colic alone are often highly suggestive of passage of a kidney stone. A patient may complain of severe flank or abdominal pain radiating to the lower abdomen or groin area. The pain of renal colic is described often as sharp, severe, intermittent, and occurring with abrupt onset. Nausea and vomiting often accompany these symptoms. If infection and obstruction is present, the patient may experience fevers and chills. Stones can, however, present without any symptoms. Frequent urination or the constant urge to urinate are symptoms that are commonly seen as the stone is passing from the ureter into the bladder. Medications including steroids, antacids, water pills, colchicine, and chemotherapeutic agents may predispose to stone formation. Past medical history including hyperparathyroidism, renal tubular acidosis, recurrent urinary infections, gastrointestinal diseases, diarrhea, prior stones, and prior urologic surgeries should be elicited during the history. On physical examination the patient often appears restless, unable to find a comfortable position. The abdomen may be slightly distended and pain is often elicited by gently tapping on the flank region.
Initial laboratory tests include:
- urinalysis to assess for the presence of blood in the urine
- blood tests to determine kidney function, blood count, and concentrations of calcium, phosphate and uric acid
- urine culture to assess for the presence of urinary infection
For patients who are considered high risk stone formers (e.g. genetic predisposition, cystine or uric acid stones, infection stones, recurrent or bilateral stones, stones in children) a more complete evaluation is mandated. This includes a 24-hour collection of urine to test for oxalate, calcium, magnesium, citrate, and uric acid levels. In addition, further blood tests including a test to rule out hyperparathyroidism may be performed. All stones that are spontaneously passed in the urine must be collected and analyzed to determine the precise stone composition.
All individuals with stones should undergo radiologic evaluation. An entire battery of radiologic procedures exist and are aimed at confirming the presence of a kidney stone, pinpointing the precise location of the stone within the urinary tract, assessing for the presence of urinary obstruction, and determining the number and approximate size of the stone(s). Each of the radiologic modalities will be discussed individually.
Plain Abdominal X-ray ("KUB" or Kidney-Ureter-Bladder X-ray)
The first radiologic test that is performed is the plain abdominal X-ray or KUB. Because the majority of stones (90%) are radiopaque, these can be easily identified on X-rays. The number, size, and approximate location of the stone can also be assessed. Because of their radiolucent nature, uric acid and some cystine stones may not appear on plan X-rays.
Intravenous Pyelogram (IVP)
An intravenous pyelogram is a series of four to six plain abdominal X-rays which are taken after the administration of intravenous contrast material which is excreted by the kidneys into the urinary tract. This provides anatomic detail of the entire urinary system from the kidneys, ureters, down to the bladder. Urologists use this as a "road map" to identify and pinpoint the precise location of the stone along the urinary tract. This also allows for the identification of urinary obstruction from an impacted stone. Anatomic abnormalities, such as duplicate ureters or a pelvic kidney, can also be identified with this test.
Computed Tomography (CT scan)
Although more expensive than an IVP test, a CT scan of the entire abdomen and pelvis provides not only identification of a stone and its location and assess for the presence of obstruction or anatomic abnormalities, but also it provides better anatomic definition of the kidney, bladder, and surrounding organs. Similar to the IVP, this test is best performed with the administration of intravenous contrast. However, if a patient is allergic to intravenous contrast, this may be omitted. Oral contrast may be used to delineate the gastrointestinal tract. All stones, including uric acid stones will appear on a CT scan.
Sonography is often used for patients in whom intravenous contrast is contraindicated. Sonograms provide excellent assessments of the kidneys and bladder, but are inferior to the IVP and CT scan in evaluation of the ureters. The presence of all stones types within the kidney can be identified by sonography. The size and position of the stone can be assessed by ultrasound guidance. The finding of a dilated kidney on sonography may suggest the presence of obstruction lower downstream within the ureter. The advantage of ultrasonography is that it avoids the exposure to radiation. The disadvantage, as mentioned above, lies in its inability to follow the course of the small and often tortuous ureters.