Bone mineral density (BMD) measurement

Bone mineral density (BMD) measurement is currently the best method of identifying those at risk of osteoporotic fractures and should be carried out on individuals with any of the risk factors. The lower the BMD the higher the risk for fracture is.

Aims of bone mineral densitometry

  • To detect patients at risk of developing osteoporotic fractures
  • To confirm the presence of osteoporosis
  • To monitor a patient's response to therapy

Indications for the diagnostic use of bone densitometry

  • Radiographic evidence of osteopenia and /or vertebral deformity
  • Previous fragility fracture
  • Loss of height, thoracic kyphosis
  • Presence of strong risk factors

Technique used to measure BMD

The most accurate currently accepted technique for assessing fracture risk in an individual is dual energy X-ray absorptiometry or DXA. This method emits a negligible amount of radiation, measures bone density at the spine and hip and has extensive normal reference data. Lumbar spine measurements may be falsely high if the patient has spinal osteophytes, crush fractures, scoliosis, sclerotic processes or aortic calcification, which causes difficulty in monitoring treatment.

Interpreting DXA results

The results of the scans are plotted against the normal range for age and the BMD score can be seen as a (+). This allows one to compare the individual's BMD to the average BMD of an age and sex matched group. The BMD scores can be expressed in terms of standard deviations (SD) from the mean bone density of young people (T- score) or an age matched population (Z-score). The risk of hip fracture increases more than 2.5 times for each standard deviation decrease in hip BMD.

Indications for Management
T score    Fracture risk Action
T > -1.0
(normal)
Low Lifestyle advice
T –1.0 to –2.5
(low bone density)  
Above average Lifestyle advice
Calcium + vitamin D    
T < -2.5 
(osteoporosis) 
High Lifestyle advice
Calcium + vitamin D
Treatment
T <-2.5 plus
one or more fractures
(established osteoporosis)   

Very high Lifestyle advice
Pain control
Exclude secondary causes     
Calcium + vitamin D 
Treatment