How often should you have a DEXA scan?

The answer differs completely depending on which scan you mean. Bone density changes slowly and is usually repeated every two years or more. Body composition changes far faster and can be usefully repeated every four to six months.

Bone Density Scanning

Bone density changes gradually. Typical rates of loss are around 1% per year, rising to more in the years around the menopause, and treatment produces gains of a similar order.

Against that, every measurement carries a margin of error. If the change between two scans is smaller than the measurement error — the least significant change — you cannot tell whether anything has actually happened [2]. Scanning too frequently produces numbers that move for no reason and prompts decisions that are not supported by real change.

As a general guide:

• Normal result, no significant risk factors — five years, or longer. There is little to gain from earlier repetition.
• Osteopenia — two to three years, with the interval shorter for those closer to the osteoporosis threshold and longer for those closer to normal [1].
• Osteoporosis, or on treatment — around two years, to assess response.
• Rapidly changing circumstances — a shorter interval may be justified where there is a new high-dose steroid course, a new fracture, substantial rapid weight loss, or a newly identified condition affecting bone. This is a clinical judgement rather than a rule.

Body Composition Scanning

Body composition responds to training, nutrition and medication over weeks rather than years, and DEXA measures it precisely enough — around 1 to 2% for fat mass — that real change over a few months is detectable.

Four to six months is a sensible interval during active change: a period of weight loss, a training block, starting testosterone replacement, or monitoring muscle mass with age. Annually is reasonable otherwise.

For anything shorter than that, bioimpedance is the more practical tool. It is quick and inexpensive enough to use every two to four weeks, and provided the conditions are kept consistent, it shows the direction of travel between DEXA scans.

Why the same machine matters

Scanners differ. Different manufacturers use different reference databases and calibration, and even two machines of the same model produce results that are not directly interchangeable.

The differences are large enough to obscure or invent change. A scan showing a fall in bone density may be recording a change of machine rather than a change in you.

Wherever possible, repeat scanning should be done on the same machine, and previous scans should be provided to the reporting clinician so the comparison is made properly rather than by reading two separate reports side by side.

Scanning more often is not better

It is worth being plain about this. More frequent scanning does not produce better information about bone. It produces the same information with more noise around it, and noise invites action that is not warranted.

The exception is where circumstances have genuinely changed. A new fracture, a new medication, a new diagnosis, or a period of rapid weight loss all change what the previous scan means, and are a reason to reassess.