Can a Cast Affect a Bone Density Scan?

Yes, a cast can affect a bone density scan if the scan measures the bone covered by the cast. Most standard DXA scans measure the hip and lower spine, so a cast on the wrist or forearm may not affect those areas. If the cast covers the area being scanned, the material can interfere with image analysis. Tell the imaging team before the appointment.

Does a cast interfere with every type of bone density scan?

No. The effect depends mainly on which part of the body is being examined and the material used to make the cast. A bone density scan, also called a DXA or DEXA scan, uses low-dose X-rays to measure bone mineral density.

According to RadiologyInfo, a patient-information service supported by the American College of Radiology and the Radiological Society of North America, most standard DXA examinations measure the lower spine and hips. Some examinations use different body sites, depending on the clinical reason for testing.

For example, a person wearing a wrist cast may still be able to undergo a standard hip and spine scan. The cast is less likely to interfere directly with measurements taken at those separate sites. However, the imaging team should know about the cast because the examination plan and positioning may need to be adjusted.

Can a cast affect a forearm or wrist bone density scan?

Yes, a cast can interfere with a scan that measures the bone underneath it. This is particularly relevant when the forearm or wrist is the specific area being examined.

MedlinePlus explains that bone density testing can measure the wrist, hand, or forearm, depending on the type of examination. A forearm scan may be requested when the hip or spine cannot be measured or interpreted reliably, or for certain medical conditions.

The cast's material matters. A study indexed by the U.S. National Library of Medicine's PubMed database examined forearm DXA scans performed through different casting materials. The researchers found that standard fiberglass casting tape interfered with the software's ability to identify bone edges in some images, making certain measurements less precise. A specific radiolucent polyester-based casting tape allowed accurate measurements in the study. These findings do not mean that every cast makes a scan inaccurate; the effect depends on the cast and the imaging method.

Will the imaging center need to remove the cast?

Not necessarily. Whether a scan can be performed with a cast in place depends on the area being examined, the casting material, and the equipment available. Some examinations may proceed as planned, while others may require a different approach or a new appointment after the cast is removed.

The NHS guidance on how a bone density scan is performed explains that the scanning team positions the patient so the appropriate body area can be measured. When a cast limits normal positioning or covers the area of interest, the team needs to decide whether a reliable examination is possible.

Do not remove, loosen, or alter a cast yourself to prepare for a bone density scan. Contact the imaging center before attending and explain which limb is in a cast, why it was applied, and when it was fitted. The team can then advise whether to proceed, modify the examination, or arrange testing at another time.

Can wearing a cast change bone density itself?

Yes. This is a separate issue from interference caused by the cast material. Immobilization limits movement and loading of the affected limb, and bone mineral measurements in that area can change during recovery from an injury.

The U.S. National Library of Medicine's PubMed summary of a study involving children and teenagers with wrist or forearm fractures describes lower bone mineral measurements in the injured upper limb when the cast was removed compared with the uninjured limb. In the participants who completed follow-up, the researchers found no remaining decrease at the examined upper-limb sites at six and 18 months. These findings concern a specific group of young people and should not automatically be applied to every age group or injury.

Consequently, a lower measurement in an injured or immobilized area may reflect an actual change in the bone, interference from the cast, or a combination of factors. The clinician interpreting the scan needs to know about the injury and the timing of immobilization to assess the findings appropriately.

What should you tell the bone density scan technician?

Before the examination, tell the imaging team that you have a cast, even if you believe it is outside the area being scanned. Explain which bone or joint was injured and whether the cast is made of plaster, fiberglass, or another material, if you know. Also mention when the injury occurred and whether you have had any recent imaging of the affected area.

The International Society for Clinical Densitometry recommends measuring bone density at the spine and hip in adults, with forearm measurements used in selected circumstances, including when the hip or spine cannot be measured or interpreted. Knowing the reason for the scan helps the imaging team determine whether another measurement site is suitable.

If the cast covers the area that needs to be measured, ask whether the scan can produce a reliable result while the cast remains in place. Depending on the circumstances, the team may be able to proceed, use an appropriate alternative, or recommend rescheduling. The cast should remain in place unless the healthcare professional responsible for your injury advises otherwise.

What if you already had a bone density scan with a cast?

If you have already completed the scan, tell the clinician who ordered it that you were wearing a cast at the time. Include the location of the cast and whether the scan measured the affected limb. This information can help the clinician and radiology team decide whether the measurements can be interpreted confidently or whether additional testing is needed.

A cast does not automatically invalidate a bone density scan. If the examination measured an unaffected area, the presence of a cast elsewhere may have little direct impact. If the cast covered the measured bone, however, the report may need careful review because the cast material or changes associated with immobilization can affect interpretation.

The most useful next step is to ask the imaging center or ordering clinician whether the cast overlapped the specific area measured and whether that affected the reliability of the results.