(Renal Scan, Renogram, Renal Scintigraphy)
What is a kidney scan?
A kidney scan is a specialized radiology procedure used to assess the function and structure of the kidneys, as well as the perfusion (blood flow) to the kidney tissue.
A kidney scan is a type of nuclear radiology procedure. This means that a tiny amount of a radioactive substance is used during the procedure to assist in the examination of the kidneys. The radioactive substance, called a radionuclide (radiopharmaceutical or radioactive tracer), is absorbed by normal kidney tissue.
The radionuclide used in kidney scans is usually a form of either technetium or iodine. The specific radionuclide used in a kidney scan depends on the type of information needed. Once absorbed into the kidney tissue, the radionuclide emits a type of radiation, called gamma radiation. The gamma radiation is detected by a scanner, which processes the information into a picture of the kidneys.
By measuring the behavior of the radionuclide in the body during a nuclear scan, the physician can assess and diagnose various conditions, such as tumors, abscesses, hematomas, organ enlargement, or cysts. A nuclear scan may also be used to assess organ function and blood circulation.
The areas where the radionuclide collects in greater amounts are called "hot spots." The areas that do not absorb the radionuclide and appear less bright on the scan image are referred to as "cold spots."
Other related procedures that may be used to diagnose problems of the kidney include abdominal X-ray, kidney, ureters, and bladder (KUB) X-rays, computed tomography (CT scan) of the kidney, kidney ultrasound, intravenous pyelogram (IVP), cystography, cystometry, cystoscopy, renal angiogram, uroflowmetry, renal venogram, or a kidney biopsy. Please see these procedures for additional information.
How do the kidneys work?
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The body takes nutrients from food and converts them to energy. After the body has taken the food that it needs, waste products are left behind in the bowel and in the blood.
The kidneys and urinary system keep chemicals, such as potassium and sodium, and water in balance, and remove a type of waste, called urea, from the blood. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys.
Two kidneys, a pair of purplish-brown organs, are located below the ribs toward the middle of the back. Their function is to:
Remove liquid waste from the blood in the form of urine
Keep a stable balance of salts and other substances in the blood
Produce erythropoietin, a hormone that aids the formation of red blood cells
Regulate blood pressure
The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule.
Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.
Reasons for the procedure
There are several types of kidney scans used to evaluate the kidneys. One or more different types of scans may be performed during a single procedure, depending on the type of information needed to diagnose the kidney condition. A renal scan is particularly useful when a patient has a known sensitivity to contrast media or underlying renal insufficiency.
To evaluate perfusion to the kidney tissue, a renal blood flow scan may be done. This type of scan may show decreased blood flow to the kidneys due to a blockage or narrowing of blood vessels to the kidneys. A renal blood flow scan may also be used to assess renovascular hypertension (high blood pressure in the kidney's blood vessels), rejection of a transplanted kidney, or the presence of renal cell carcinoma (cancer of the kidney).
A renal structural scan may be used to examine the structure of the kidneys. Conditions that may affect the size and/or shape of the kidneys include tumors, cysts, abscesses, and congenital disorders. This type of scan may also be used to detect rejection of a transplanted kidney.
The function of the kidneys can be assessed by a renal function scan (renogram). This scan measures the amount of time needed to absorb and/or excrete the radionuclide. A renal function scan may be repeated periodically to assess the response of the kidneys to treatment.
One of the primary causes of kidney problems is renovascular hypertension. A renal hypertension scan may be performed to detect this condition, as well as the source of the condition. A renal hypertension scan may also be used to assess the potential response of the renal blood pressure to treatments such as medication, surgery, or vascular procedures such as angioplasty.
Obstruction of one or more portions of the urinary tract can cause kidney problems. A renal obstruction scan may be performed to assess the presence and location of an obstruction.
There may be other reasons for your physician to recommend a kidney scan.
Risks of the procedure
The amount of the radionuclide injected into your vein for the procedure is small enough that there is no need for precautions against radioactive exposure. Most of the radiation is gone from the body within 24 hours. The injection of the radionuclide may cause some slight discomfort. Allergic reactions to the radionuclide are rare, but may occur.
For some patients, having to lie still on the scanning table for the length of the procedure may cause some discomfort or pain.
Patients who are allergic to or sensitive to medications, contrast dyes, or latex should notify their physician.
If you are pregnant or suspect that you may be pregnant, you should notify your physician due to the risk of injury to the fetus from a kidney scan. If you are lactating, or breastfeeding, you should notify your physician due to the risk of contaminating breast milk with the radionuclide.
There may be other risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician prior to the procedure.
Certain factors or conditions may interfere with the accuracy of a kidney scan. These factors include, but are not limited to, the following:
Presence of a radionuclide in the body from a previous nuclear medicine procedure within a certain period of time
Barium remaining in the gastrointestinal (GI) tract from a recent barium procedure
Medications such as diuretics (water pills), ACE inhibitors (heart/blood pressure pills), and beta blockers (heart/blood pressure pills), which may affect the results of a renal function scan
Intravenous pyelogram (IVP) procedure done within 24 hours of a renal scan may affect kidney function
Before the procedure
Your physician will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
You will be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.
Generally, no prior preparation, such as fasting or sedation, is required prior to a kidney scan.
You may be asked to drink several glasses of water prior to the procedure.
Notify the radiologist or technologist if you are allergic to or sensitive to latex, medications, contrast dyes, or iodine.
If you are pregnant or suspect you may be pregnant, you should notify your physician.
If you are taking medication for high blood pressure, your physician may ask you to stop the medication for a period of time prior to the procedure.
Based upon your medical condition, your physician may request other specific preparation.
During the procedure
A kidney scan may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your physician's practices.
Generally, a kidney scan follows this process:
You will be asked to remove any clothing, jewelry, or other objects that may interfere with the procedure.
You will be asked to remove clothing and will be given a gown to wear.
An IV line will be started in the hand or arm for injection of the radionuclide.
The radionuclide will be injected into your vein. The radionuclide will be allowed to concentrate in the kidney tissue for a short period.
You may be asked to either lie down or sit upright on a scanning table. You will need to remain still during the procedure, as any movement may affect the quality of the scan. For a structural renal scan, you will need to lie still during the entire procedure.
The scanner will be placed over the kidney area in order to detect the gamma rays emitted by the radionuclide in the kidney tissue.
Depending on the type of scan being performed, you may receive a diuretic medication or an ACE inhibitor medication during the procedure.
When the scan has been completed, the IV line will be removed.
While the kidney scan itself causes no pain, having to remain still for the length of the procedure might cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.
After the procedure
You should move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness from lying flat for the length of the procedure.
You may be instructed to drink plenty of fluids and empty your bladder frequently for about 24 hours after the procedure to help flush the remaining radionuclide from your body.
The IV site will be checked for any signs of redness or swelling. If you notice any pain, redness, and/or swelling at the IV site after you return home following your procedure, you should notify your physician as this may indicate an infection or other type of reaction.
You may resume your usual diet and activities, unless your physician advises you differently. Your physician may give you additional or alternate instructions after the procedure, depending on your particular situation.