A bone density scan measures the quantity of bone. The most common way to measure bone density is with a dual-energy x-ray absorptiometry called DXA for short.
The most common sites of measurement are the hip and lumbar area of the spine. In some instances, the forearm is also measured.
Your measurements are compared to a database of same-sex younger individuals to calculate is standardized number called a T-score. In addition, your results are compared to same-sex individuals of the same age to calculate a “Z-score.”
The T-score is used for diagnosis. The categories for diagnosis are:
- normal (T-score -1.0 and above)
- low bone mass, referred to as osteopenia (T-score between -1.0 and -2.5)
- osteoporosis (T-score -2.5 and below)
- severe osteoporosis (T-score -2.5 and below with history of a fracture)
Assess Risk Factors with Low Bone Mass/Osteopenia
For those individuals in the low bone mass category, calculation of an additional score that assesses risk factors along with the bone density of the neck region of your hip is recommended. You will be asked about certain risk factors along with measurement of your height and weight. This information is used to calculate your risk of fracture in the next 10 years for a hip fracture or major osteoporotic fracture. This so-called FRAX score is either calculated as part of the bone density scan software or through an interactive web-based or app calculator.
Should you have a bone density scan?
Bone density scans are recommended for
Individuals at risk for osteoporosis including
Women in the menopause transition or early menopause
Men over age 50
Women age 65 and older
Men age 70 and older
Talk with your doctor or healthcare professional about your risk for osteoporosis if it’s time to get a bone density scan.
When should you repeat a bone density scan?
Timing for a follow-up bone density scan is based on your baseline scan results, your medical history or treatment, and the expected amount of change. Medicare and commercial insurance carriers usually reimburse for DXA scans at 24-month intervals. In circumstances of possible rapid loss such as high dose steroid therapy, your insurer may approve a shorter interval for a follow-up scan.
You should return to the same location to have your repeat bone density. Unfortunately, comparison cannot be made from results of different machines.