​Given that osteoporosis therapy may only produce a few % increase in bone mineral density (BMD), very precise tests are needed. BMD by Dual-energy X-ray Absorptiometry (DXA) can be used to assess response to therapy. Serial measurements therefore must be carried out on the same unit and random fluctuation not confused with real change.

The variability between tests is about 1-3% as stated above. The absolute BMD (g/cm2) should be used to determine change, NOT the T-score. Each DEXA unit measures its precision and can report the least significant change detectable. Because of these limitations, BMD every two years is recommended in general for patients with prostate cancer on androgen ablation (AA). In patients with other risk factors that may accelerate bone loss or where baseline osteopenia is detected, 18 month (rarely 12 months) follow-up BMDs may be justified. Such patients may be best managed under specialist care. Treatment should not be stopped or changed solely on the basis of the BMD.