Kidney Stone Tests |Blood, Urine, X-Ray, Ultrasound, CT Scan, MRI

The presence of signs and symptoms of a kidney stone may prompt further tests and investigations to confirm the presence of a stone, identify the location, size, shape and type of kidney stone and indicate a possible cause of the kidney stone.

Some of these tests can be conducted immediately, like a urine dipstick, while other tests would require blood and urine samples to be sent to a laboratory for further analysis. Investigations may be conducted in-house within the doctor’s surgery, like an ultrasound, or require further procedures at a clinic or hospital with suitable facilities, like a, x-ray, CT scan or MRI. In most cases, these tests and investigations will not require hospitalization.

Tests for Kidney Stones

Urine Dipstick

A sample of the mid stream urine is collected in a clean, sterile container and a urine dipstick is inserted into the sample. This will reveal the presence of the following in the urine :

• Protein (proteinuria)
• Blood (hematuria)
• Glucose (glycosuria)
• Leucocytes (white blood cells)
• pH (acidity or alkalinity)

24 Hour Urine Test

Urine is collected for a 24 hour period and sent for laboratory analysis (urinalysis). This can be done at home where urine is collected in small containers and transferred to a large container which will hold all the urine during the collection period. This large container will be handed in to the doctor or laboratory.

Urinalysis will reveal the following in the urine :

• Urea
• Creatinine
• Calcium
• Oxalate
• Uric Acid
• Sodium
• Leucocytes (white blood cells)
• Red blood cells

A urine culture may be necessary to identify any pathogenic bacteria responsible for a urinary tract infection.

Blood Tests

Your doctor or nurse will collect one or more blood samples which is sent for laboratory analysis. These samples will reveal the presence of the following in the blood :

• Urea and Electrolytes (U&E)
• Calcium
• Phosphate
• Uric Acid

In cases of recurrent calcium kidney stones, the level of parathyroid hormone in the blood may also be tested.

Investigations for Kidney Stones

Imaging studies are done to confirm the presence of a kidney stone, identify the location, size and shape of the stone and assess the degree of obstruction caused by the stone.

Abdominal (KUB) X-Ray

An abdominal x-ray, also referred to as a KUB x-ray (Kidney-Ureter-Bladder), may be sufficient to identify the presence and location of a stone. Most kidney stones (about 80% of cases) are visible with an abdominal x-ray. Those kidney stones that are not visible on an x-ray are usually detected on a CT scan. An x-ray should be avoided in pregnant women due to the use of radioactive material.

There are two techniques to highlight the urinary tract on an x-ray and better assess the size and shape of the kidney stone as well as any obstruction that it may be causing.

1. IV pyelogram (IVP) is where contrast material (radiocontrast dye) is injected into a vein. A series of x-rays will be taken at different intervals.
2. Retrograde pyelogram is where the contrast material is injected into the ureters.

Ultrasound (Ultrasonography)

Ultrasonography is the use of ultrasonic waves to create an image of the area and should not be confused with shock wave treatment to break down kidney stones. Ultrasonography is a diagnostic procedure and it is the preferred option for pregnant women. While it is a quick and easy procedure that can be conducted on the examination bed, kidney stones may be missed by this imaging technique, especially if the operator is not skilled at interpreting the images.

Spiral Computed Tomography (CT) Scan

This is the preferred imaging technique for identifying the location, shape and size of the kidney stone. It provides multiple views of the target area and does not require any radiocontrast dye. It is able to isolate up to 99% of kidney stones.

Magnetic Resonance Imaging (MRI)

This is not a widely used investigative technique for identifying kidney stones. Unlike an x-ray and CT scan, it does not use any radiation so it may be a better option for pregnant women if an ultrasound scan is not helpful.