A bone scan is an imaging test used to help diagnose problems with your bones. It safely uses a very small amount of a radioactive drug called a radiopharmaceutical. It has also been referred to as a “dye” but it does not stain the tissue.

Specifically, a bone scan is done to reveal problems with bone metabolism. Bone metabolism refers to the process in which bones break down and rebuild themselves. New bone formation is part of the healing process when bones are injured or broken. A bone scan is a good way to view and document abnormal metabolic activity in the bones.

A bone scan can also be used to determine whether cancer has spread to the bones from another area of the body, such as the prostate or breast.

During a bone scan, a radioactive dye is injected into your bones. You’ll then be monitored for several hours. A very small amount of radiation is used in the dye, and nearly all of it is released from your body within two or three days.

Your doctor may order a bone scan if they think you have a problem in your bones. A bone scan can also help find the cause of any unexplained bone pain you’re experiencing.

Bone scans may reveal bone problems associated with the following conditions:

  • arthritis
  • avascular necrosis (when bone tissue dies due to a lack of blood supply)
  • bone cancers
  • cancer that has spread to the bone from other parts of the body
  • fibrous dysplasia (a condition that causes abnormal scar-like tissue to grow in place of normal bone)
  • fractures
  • infection involving the bone
  • Paget’s disease of the bone (a disease that causes weak, deformed bones)

A bone scan carries no greater risk than conventional X-rays. The tracers in the radioactive dye used in a bone scan produce very little radiation exposure. The risk of having an allergic reaction to the tracers is low.

However, the test may be unsafe for pregnant or breastfeeding women. There is a risk of injury to the fetus and of contaminating the breast milk. Make sure to tell your doctor if you’re pregnant or breastfeeding.

A bone scan requires no special preparation. Before the scan, your doctor will ask you to take off jewelry with metal, including body piercings.

The actual screening procedure takes about an hour. Your doctor may give you a mild sedative to help you relax if you think you’ll have problems sitting still for that amount of time.

The procedure begins with an injection of radioactive dye in your arm. The dye is then allowed to work its way through your body for the next two to four hours. Depending on the reason for the bone scan, your doctor may begin imaging immediately.

As the dye spreads through your body, the bone’s cells naturally gravitate to areas that need repair. The dye’s radioactive tracers follow these cells and collect in spots where bone is damaged.

After enough time has passed, your doctor will use a special camera to scan the bones. The damaged areas — where the dye has settled — appear as dark spots on the image.

Your doctor may repeat the injection and imaging process if the first round wasn’t conclusive. They may also order a single-photon emission computed tomography (SPECT). This is similar to a bone scan, except the imaging process creates 3-D images of your bones. A SPECT is necessary if your doctor needs to see deeper into your bones. They may also use it if the original images weren’t clear in certain areas.

Test results are considered normal when the dye is spread evenly throughout the body. This means that you likely don’t have a major bone problem.

Results are considered abnormal when the scan shows darker “hot spots” or lighter “cold spots” in the bones. Hot spots describe places where an excess of dye has collected. Cold spots, on the other hand, are areas where the dye didn’t collect at all. Abnormal results can indicate that you have a bone disorder, such as cancer or arthritis.

A bone scan doesn’t cause any side effects or complications. Most of the radioactive tracer in the dye is eliminated from your body within 24 hours. Small amounts may remain for as long as three days.

While the test can help identify problems in bone metabolism, it doesn’t necessarily reveal the reason for them. A bone scan tells that there is a problem and where it is located. It is a nonspecific test. You may have to undergo more tests if the bone scan showed abnormalities. Your doctor will explain your options and help guide you through the process.