324 Obstetrics and Gynecology Board Review •••
❍ Who should have tests for bone mineral density (BMD) (DXA scan)?
All women 65 years or older without risk factors.
All postmenopausal women younger than 65 with risk factors.
All postmenopausal women younger than 65 with a history of fracture.
All postmenopausal women considering therapy for osteoporosis.
All women on estrogen/progestogen therapy for a prolonged period (National Osteoporosis Foundation Guidelines).
❍ How is osteoporosis diagnosed? What is the most accurate technique available for measuring bone density?
Using dual energy absorptiometry (DXA) measuring the hip and lumbar spine (central DXA). This is the most
accurate technique available for measuring bone density. DXA scans are reported using a T score.
❍ What hip areas are routinely assessed for BMD using a DXA scan?
The femoral neck, trochanter, Ward’s triangle, and intertrochanter.
❍ What areas are most reproducible on DXA?
A-P spine and femoral neck.
❍ What is the ideal screening interval for DXA?
Every 2 years.
❍ Can a peripheral DXA (heel, finger, wrist) be used to diagnose osteoporosis?
No. These are used to screen for osteoporosis. The diagnosis is made by central DXA.
❍ Can a peripheral DXA be used to predict fracture risk?
Yes (NORA trial).
❍ What is the T score?
A measurement of BMD that indicates the number of standard deviations above or below the average peak bone
mass in a young woman.
❍ What does the T score indicate?
A T score of –1.0 is one standard deviation below peak bone mass, and represents about a 10% loss in bone mass
at the site measured.
❍ What is the Z score?
This number indicates the number of standard deviations from average bone mass compared with a population the
same age. If there is a significant variance, one should look for secondary causes of osteoporosis.
❍ Does the T score correlate with fracture risk?
Yes. For each T score below normal the risk of fracture doubles at that site. (A T score of -1.0 doubles the fracture
risk compared with a T score of 0.0.)