Best practices in assessing BMD
Accurate and reliable measurements of bone mineral density (BMD) are important to ensure validity of results, and clinicians should adhere to available standards to achieve this, said Dr John Carey, President of the International Society for Clinical Densitometry (ISCD) during the AFOS 2017 Annual Meeting in Kuala Lumpur, Malaysia.
“Quality BMD testing entails testing the right people, performing accurate and reliable test, preparing high-quality report … This will improve diagnosis and treatment of those most likely to benefit, and reduce or avoid unnecessary testing or treatment among those least likely to benefit,” he said.
When scanning the hip, optimal positioning and necessary attributes are important, emphasized Carey. “Put simply, that means having a straight femoral shaft with correct femoral rotation, there should be no obvious artefacts and motion, and the greater trochanter should be centred and situated vertically. You should be able to see a little lobe at the left of the trochanter if it is rotated appropriately.”
“For the spine, it should be straight, centred, includes anatomical landmarks [in the spine like] T12 [to the entire L1-L4 region], and like the upper margins of the sacroiliac joints. There should be no movement or artefacts present, similarly to other regions.”
According to the ISCD position paper, the preferred skeletal sites for taking BMD measurements in children are the lumbar spine and total body less head. In adults, femoral neck, lumbar spine (L1-L4), and total hip are preferred sites, while the distal 1/3 radius is also recommended in some instances, highlighted Carey.
The ISCD position paper also states that postmenopausal women and men aged >50 years can be diagnosed using the T-score while for younger men and premenopausal women, the Z-score is recommended instead.
“If you have had a fragility fracture [previously], clearly you already have osteoporosis. … [In this case,] DXA* is not used for diagnosis, it is used for monitoring and assessing prognosis. For people who haven’t had a fracture, you can also use DXA to assess risk of fracture,” said Carey.
Repeated measures require knowledge and further refinements of the least significant change (LSC), he explained, adding that the acceptable standards for LSC are <6.9 percent for femoral neck, <5.0 percent for total proximal femur, and <5.3 percent for the lumbar spine.
How to avoid pitfalls
“The only thing that is worse than not having access to BMD test is having access to a really bad one,” cautioned Carey. “Providing appropriate training, certification, and support to DXA technologists and interpreters can help assure quality bone densitometry.”
On the other hand, the flipside of having a low-quality BMD testing is having an overdiagnosis, he said. “We get credit for curing diseases that never would have harmed the patient. And we do see collateral damage of our well-intentioned efforts.”
To avoid pitfalls in densitometry testing, healthcare professionals should strive to become experts through training, reading, and case discussion, apply ISCD quality measures for scanning patients and interpreting their results, keep up-to-date with ISCD courses, certification, publication, and take a good patient history, advised Carey.
Concluding his talk with humour, Carey said, “In life, you only need three bones, a back bone, a funny bone, and a wishbone.”