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Patients Recommended for
Bone Mineral Density Measurements:
- Post-menopausal women with at least one
additional risk factor (other than menopause).
- All women older than 65 regardless of
risk factors.
- Post-menopausal women who present with
fractures.
- Women considering therapy for
osteoporosis, if bone mineral density (BMD) testing would affect the decision.
- Women who have been on hormone
replacement therapy (HRT) for prolonged periods of time.
Medicare Guidelines for Bone
Densitometry:
- Estrogen deficient women at clinical
risk for osteoporosis.
- Individuals with vertebral
abnormalities.
- Individuals receiving, or planning to
receive, long-term glucocorticoids.
- Individuals with primary
hyperparathyroidism.
- Individuals being monitored to assess
the response of efficacy of an approved osteoporosis drug therapy.
- Medicare will only reimburse when BMD
tests are ordered by the treating health care provider.
- Frequency of BMD testing is once per two
years.
- Benefit applies to all Medicare patients
including managed care programs.
- Non-Medicare payers may have different
guidelines.
Understanding the Results of Bone Mineral
Density Tests: T-score and Z-score
Bone mineral density (BMD) tests are
performed to determine whether a patient has osteoporosis or osteopenia, a low bone mass
that puts her at risk for osteoporosis. To make this determination, the technologist will
calculate the patient’s T-score. The World Health Organization (WHO) established the
criteria for determining the T-score.
To calculate a patient’s T-score,
physicians subtract the patient’s measured BMD from a BMD reference range of women in
their thirties (YN = young normal). Around age 35, bone mass is usually at its peak and
fracture risk is at its lowest. This figure is then divided by the standard deviation
(SD).
T Score = (BMD –
YN) / SD
By determining a patient’s
T-score, the physician will see whether a woman has or is at risk for osteoporosis:
T-Score: WHO Criteria for Osteoporosis in Women |
| Normal |
BMD
> -1.0 below the young adult reference range |
| Low
Bone Mass (Osteopenia) |
BMD
is -1.0 to -2.5 SD below the young adult reference range |
| Osteoporosis
|
BMD
< -2.5 SD below the young adult reference range |
| Severe
Osteoporosis |
BMD
< -2.5 SD below the young adult reference range and the patient has one or more
fractures |
As a rule, a patient’s
fracture risk doubles for every SD (standard deviation) below the young adult reference
range. For example, if a patients’ T-score is -2 SD, she is at four times greater
risk of a fracture than a young woman at peak bone density.
Physicians may also measure a
patient’s Z-score with a bone mineral density test. The Z-score compares the
patient’s measured BMD to the average BMD measurement for the patient’s age and
sex. The Z-score is not used to confirm a diagnosis of osteoporosis because a favorable
BMD measurement (compared to the average BMD measurement for the patient’s age group)
does not mean the patient is not at risk for osteoporosis.
Bone mineral density increases until
around age 35 and then levels off until menopause. During the first six to eight years of
menopause, there is a sharp decline in bone mineral density. It is estimated that between
1% and 5% of bone density is lost at this time. The higher a woman’s overall bone
density, the less she will be affected when she loses bone density at menopause.
Updated: April 7, 2008
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