(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?
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).