DEXA Bone Density Scans – accuracy depends on where it is done

If you are considering having a DEXA bone density scan to assess your risk of osteoporosis, where you have it done will significantly impact the accuracy of the results, and whether they will provide you with the information you want.

While dual-energy X-ray absorptiometry (DEXA) bone density scans are considered the gold standard for assessing bone mineral density (BMD), it is important to note that there is a large difference in the accuracy of DEXA scans obtained from non-accredited imaging centers offering bone density scans as a service, and facilities specializing in bone densitometry (the clinical assessment of bone density). An accurate scan enables doctors to rule out or establish a diagnosis and provides opportunity for timely treatment recommendations, including dietary and lifestyle modifications.

To illustrate the difference, the first part of the article will explain the standards for accredited facilities, and then contrast them to non-accredited imaging centers. This comparison will underscore the differences between the two.

Accredited Facilities for DEXA Bone Density Scans

For bone density scan data to be reliable in ruling out or diagnosing osteopenia or osteoporosis, it’s important that the scans are conducted by a trained bone densitometry technologist, in a facility that adheres to accreditation standards established by the International Society for Clinical Densitometry (ISCD), and in Canada, by the local College of Physicians and Surgeons of the province. Finally, the scans must be reviewed by a Radiologist, a doctor who specializes in medical imaging before a report is generated.

In British Columbia, the accreditation of bone densitometry facilities as well ensuring that bone densitometry technologists have the appropriate training is overseen by the College of Physicians and Surgeons of British Columbia (CPSBC). They operate the Diagnostic Accreditation Program (DAP), which ensures the quality and safety of a range of diagnostic services, including DEXA bone density scans. The DAP not only verifies that a facility meets the necessary quality standards but ensures that they consistently maintain those standards.

Accredited facilities must adhere to the Accreditation Standards for Diagnostic Imaging from the College of Physicians and Surgeons(1). This comprehensive 312 page document contains imaging standards for x-rays, mammograms, ultrasounds, MRIs , with the standards for bone densitometry beginning on page 274. These standards ensure the quality and safety of bone density scanning procedures.

These standards also outline that bone densitometry facilities must have a Medical Director overseeing operations, and that bone densitometry technologists performing scans must either be certified with the International Society for Clinical Densitometry (ISCD), or have obtained 12 Continuing Medical Education (CME) credits in bone densitometry. Additionally, technologists in accredited facilities are mandated to regularly update their knowledge by acquiring 24 CME credits in bone densitometry every three years.

Summary of the Accreditation Standards for Diagnostic Imaging for Bone Densitometry

The bone densitometry section of the Accreditation Standards for Diagnostic Imaging (1) consists of ten pages of standards, including;

• • patient preparation for the exam
  • standard imaging procedure protocols to ensure that the examination is appropriate for its intended use in clinical decision making
  • ensuring that current and accurate medical records are kept for each person
  • that diagnostic reports are in a standardized format and provide comprehensive and necessary information for clinical decision making / interpretation 
  • safe operation and maintenance of equipment
  • acceptance testing for equipment to ensure it is tested prior to use, and quality assurance programs to ensure that the required quality is attained

These standards provide additional mandatory requirements and best practices that supplement the accreditation standards established by the International Society for Clinical Densitometry (ISCD) (2).

Below is the first of the ten pages of standards (this page is on patient preparation).

These standards require that the following information be collected before a bone density scan takes place.

(1) taking clinically relevant medical history, including family history, prior fractures, bone trauma, surgery, chronic illness, and any relevant medication that may affect bone density such as corticosteroids, or thyroid medications. 

(2) ensuring that the person has not had any procedures such as a barium x-ray or radionucleotide study that can affect the results,

(3) assessing whether the person has arthritis, deformity or other degenerative changes that can affect measurement,

(4) ensuring the person hasn’t had any implants in the area being assessed, such as a hip replacement,

(5) that a qualified physician is involved in assessing any interference or contraindications,

(6) review of previous bone density scans to determine if a specific site should be excluded from the current scan,

(7) patient height and weight are accurately measured at the time of examination.

None of this, or any of the other 9 pages of standards are required to be followed in an imaging center that provides bone density scans as a service. 

Imaging Center Providing DEXA bone density scans

Imaging centers that provide DEXA bone density scans as a service are businesses, and as such are not clinically regulated.  There are no physicians or radiologists involved. These businesses are not required to meet the international standards of the International Society for Clinical Densitometry (ISCD), or local clinical standards outlined above.

For example, these centres may assess the person’s height using a tape measure or meter stick attached to a wall, rather than a stadiometer. Weight may not even be measured — or even asked, but calculated from the results of a whole body composition scan performed at the same time. Estimating height and weight does not provide the quality data required to interpret the results of the Dexa scan. In addition, questions about personal medical history, family medical history, risk factors, medications or procedures that could affect results are limited, or non-existent.

Image Quality

In accredited facilities, rigorous standards are in place to ensure high image quality, as all scans undergo review by a radiologist prior to report generation.

Images are required to be clear and well defined, such as the top pair of images from HealthLink BC (3). 

Images from imaging centers, such as the pair of images on the bottom often lack the contrast and definition which limits their usefulness.

 

Measurement Accuracy – hips

For hip scans to be useful in diagnosing osteoporosis, it is essential that the neck of the femur (hip bone) is measured at the narrowest part (4), such as the image on the far right (4).

The image on the left from an imaging center does not measure the neck of the femur at the narrowest part, and as illustrated in the middle image, the narrowest part is to the right of where it was measured.

Measurement Accuracy – spine

Spinal images from accredited facilities (left photo from (4)) are clear, and show equal amounts of soft tissue on either side of the spine. In addition, the height of each vertebrae is roughly the same height, with markers in the disk space (4).

   

The image on the right from an imaging center is not clear and has little contrast. It does not show equal amounts of soft tissue on either side of the spine, and the height of each vertebrae varies considerably.

Finding an Accredited Facility

In British Columbia, a full list of accredited diagnostic imaging facilities in the province is available on the College of Physicians and Surgeons web site (5).

The International Society for Clinical Densitometry (ISCD) has a searchable list of accredited facilities by country, as well as US states and Canadian provinces.

The College of Physicians and Surgeons in your province or state may also have a list.

Final Thoughts…

For data from a DEXA bone density scan to be reliable and useful for ruling out or diagnosing osteopenia or osteoporosis, it needs to be performed at an accredited facility.

This can be compared to the difference between home lab test testing and lab tests. While at-home blood testing kits are available to screen for different conditions, diagnoses of a medical condition requires blood tests from an accredited laboratory that are reviewed and assessed by a physician.

If you want to have a DEXA bone density scan to assess your risk of osteoporosis, then speak with your doctor to get a referral to an accredited facility.

How I Can Help

If you have been diagnosed as being at risk for osteoporosis, or have been diagnosed with osteopenia or osteoporosis, implementing appropriate dietary and lifestyle changes can be beneficial.  Please let me know if you would like some support.