The importance of BMD

Evaluating patients for osteoporosis risk factors is an important step toward diagnosis.1 The presence of these factors can help doctors determine whether they should test patients’ bone mineral density, also known as BMD.

BMD is a measurement of bone mass that is used to help doctors diagnose osteoporosis.1,2 It relates to bone strength and can predict a person’s risk of future fracture.1 Although BMD testing can determine whether or not a patient has osteoporosis, a doctor also may make a diagnosis without it if a patient shows evidence of a low-trauma fracture and has osteoporosis risk factors.1

The National Osteoporosis Foundation (NOF) and the US Preventive Services Task Force both recommend BMD testing in women older than 65 and in men older than 70.1

How BMD is measured

In postmenopausal women and men older than 50, BMD is evaluated according to T-scores. T-scores are based on a system that compares a patient’s BMD to the BMD of a healthy 30-year-old.1,3

In the T-score system, the 30-year-old adult BMD is considered to be the standard score, which is set at 0. The difference between a patient’s BMD and the standard BMD is called a standard deviation, or SD.2,3 When a patient has a score of 0, +1 SD, or -1 SD, it means that patient has normal or healthy bone mass. When a patient has a negative score that’s below -1 SD, it means he or she has low bone mass, or osteopenia. A score of -2.5 SD or lower indicates osteoporosis. Patients with scores below -2.5 SD who have also had at least 1 fracture are considered to have severe or “established” osteoporosis.

WHO measurements of osteoporosis using BMD measurements at the spine, hip, or forearm
Normal BMD is within 1 SD of a young normal adult (T-score at -1.0 and above)
Low Bone Mass (Osteopenia) BMD is between 1.0 and 2.5 SD below that of a young normal adult (T-score between -1.0 and -2.5)
Osteoporosis BMD is 2.5 SD or more below that of a young normal adult (T-score at or below -2.5)
Severe/Established Osteoporosis BMD is 2.5 SD or more below that of a young normal adult (T-score at or below -2.5), plus there have been ≤1 fractures

BMD testing methods

Clinicians can measure BMD at the various points in the skeleton.1,4 Because hip fracture is the most important result of osteoporosis, it’s usually preferred to get BMD measurements from the hip.4 However, in perimenopausal women or women in early menopause, spinal BMD may be a better indicator of bone mass loss.

There are many types of imaging that can be used to measure BMD, but dual-energy X-ray absorptiometry, or DXA, is considered the standard testing method.4 This highly accurate technology involves a painless 2-dimensional scanning process.3,4 DXA can be used to measure BMD at any site, but hip and spine measurements taken through DXA are primarily used to diagnose osteoporosis, predict future fracture risk, and monitor patients’ BMD over time.1,4

  • 1. National Osteoporosis Foundation. Clinician’s Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation; 2010.
  • 2. The Free Dictionary [Internet]. Bone mineral density [definition]. Farlex; [cited 2012 Jun 17]. Available from: http://medical-dictionary.thefreedictionary.com/bone+mineral+density.
  • 3. National Institutes of Health Osteoporosis and Related Bone Diseases National Resource Center [Internet]. Bone mass measurement: what the numbers mean. National Institute of Arthritis and Musculoskeletal and Skin Diseases; [cited 2012 Jun 17]. Available from: http://www.niams.nih.gov/health_info/bone/bone_health/bone_mass_measure.asp.
  • 4. Lindsay R, Cosman F. Osteoporosis. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, editors. Harrison’s principles of internal medicine. 18th ed. Chicago: McGraw Hill; 2012. p. 3120-35.

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