Manitoba Health
Bone Density Testing Information for Professionals
Definition of Osteoporosis
The World Health Organization defines osteoporosis as "...a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture".
For comparing rates of osteoporosis in different populations the following categorization was proposed based upon bone density expressed as a T-score (the number of standard deviations above or below average peak young-adult bone density):
| T score | Interpretation |
| <1 SD below average peak BMD | Normal |
| 1-2.5 SD below average peak BMD | Low bone density (osteopenia) |
| >2.5 SD below average peak BMD | Osteoporosis |
This definition is only applicable after menopause in women or age 50 in men.
Note that "osteopenia" is a T-score category, not a disease. The term "low bone density" is now preferred to the term "osteopenia". People with "low bone density" are not necessarily at high fracture risk.
Clinical Role of Bone Density Measurement
A distinction is made between diagnostic classification and the use of bone mineral density (BMD) for fracture risk assessment. Bone density is best thought of as risk factor for fracture rather than a diagnostic threshold.Understanding bone density as a risk factor means interpreting the value in light of other key information, such as age and previous fracture. A T score of -1.8 does not predict the same risk for a fracture in a 45 year old as it does in a 69 year old.
The T-score captures only one aspect of fracture risk. In evaluating fracture risk, bone density should be considered in conjunction with other clinical risk factors for fracture. Important independent risk factors include low body weight, history of postmenopausal fracture, family history of fracture and poor neuromuscular function. Intervention should be based on fracture risk as determined by a combined assessment of BMD, age and other clinical risk factors for fracture. Treatment decisions should be based on fracture risk, not BMD alone.
Effective January 1st 2006, estimated absolute fracture risk (percent chance of having an osteoporotic fracture over the next ten years) will be used to categorize fracture risk based upon BMD, age and clinical risk factors after age 50 (an online version of the fracture risk calculator is available at: http://apps.sbgh.mb.ca/bmd-web-calculator/calculator.action. "Fracture risk" over the next 10 years is categorized using definitions similar to risk categories for cardiovascular disease:
| Fracture Risk | Definition |
| Low risk | <10% chance of an osteoporotic fracture |
| Medium risk | 10 - 20% chance of an osteoporotic fracture |
| High risk | > 20% chance of an osteoporotic fracture |
Key points when reviewing a BMD test:
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Not all risk factors for fracture are amenable to pharmacotherapy. In a non-osteoporotic individual with high risk of fracture due to falling, a falls prevention program may be preferred to pharmacotherapy. Pharmacotherapy has been most clearly shown to benefit patients with BMD in the osteoporotic range or those with established fragility fractures (especially when they affect the spine).
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T-scores should not be used as a "stand-alone" result to guide management. Many factors affect fracture risk other than BMD (older age and previous fragility fractures are the most important). Patients can still be at high risk of fracturing with bones in the low bone density (osteopenic) or normal range (now grouped together as "non-osteoporotic"). Alternately, patients can have a relatively low risk of fracturing even with bones measured in the osteoporotic range (especially if they are relatively young and do not have other risk factors).
University of Manitoba Osteoporosis Flowchart
Footnotes:
a BMD testing in individuals younger than age 50 can be considered when there are significant medical conditions or medications associated with osteoporosis. Treatment guidelines are not well defined and requires an individualized approach, bearing in mind that risk of fracture is usually low, while long term safety and efficacy of drug therapy is not well established.
b Other high-risk medication use (e.g., aromatase inhibitors for breast cancer, androgen deprivation for prostate cancer), parental hip fracture, high alcohol intake or current smoking, low body weight (< 60 kg) or major weight loss (>10% of weight at age 25)
c Definite non-traumatic vertebral fractures (>25% height loss with end-plate deformity) are associated with a 5-fold increased risk for recurrent vertebral fractures. Equivocal spine fractures are not strong indicators of osteoporosis.
d The major objective of follow-up testing is to identify individuals with continued BMD loss. The anti-fracture effect of treatment is not explained from the small change in BMD. Stable BMD is consistent with successful treatment.
Anatomy of a Bone Density Report
| INTERPRETATION | Fracture
Risk :
BMD Category : |
Medium fracture risk
13.0% 10-year risk of osteoporotic fracture 6.7% 10-year fracture risk for an average 52 year old 154 similar patients would have to be treated for 1 Osteoporotic |
| RESULTS
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| Spine
|
Levels:
BMD = T-Score = |
L1-4
0.823 g/cm2 -3.0 Borderline increase since |
| Total Hip
|
Site:
BMD = T-Score = |
Left
total hip -3.0 No change since |
Explanation of a Bone Density Report
Fracture
Risk:
|
Fracture Risk is based on the patient's
10-year risk of osteoporotic fracture: low
<10%, moderate 10-20%, or high >20%. (See Osteoporosis
Patient's Risk is estimated from age, total
hip T-score, measured BMI and the following self-reported risk factors: a
fracture after age 50, parental hip fracture after age 50, current
smoking, need to use arms to stand up from a chair, or current regular
oral steroid use.
Average Risk is the 10-year osteoporotic fracture risk for an average person of
the same age and sex.
NNT (number needed to treat) is a measure of treatment
effectiveness; the number of patients who need to be treated to prevent
one adverse outcome.
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Note: Fracture Risk is not
estimated prior to age 50.
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BMD
Category:
|
Defined
from the minimum T-score and age.
For age
50 or older: non-osteoporotic (minimum T-score above -2.5) or osteoporotic (minimum T-score -2.5 or lower).
Prior
to age 50: normal for age (Z-score above -2.0) or reduced
for age (Z-score -2.0 or lower).
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