Bone Mineral Density Measurement

Diagnosis of Osteoporosis with Bone Mineral Density Measurement

Technologists often diagnose osteoporosis by measuring a patient's bone mineral density (BMD). Bone mineral density measures the amount of calcium in regions of the bones. Most methods for measuring BMD (also called bone densitometry) are fast, non-invasive, painless and available on an outpatient basis. Bone densitometry can also be used to estimate a patient's risk of fracture. BMD methods involve taking dual energy or CT scansof bones in the spinal column, wrist, arm or leg. These methods compare the numerical density of the bone (calculated from the image), with empirical (historical) data bases of bone density to determine whether a patient has osteoporosis, and often, to what degree.

New methods of measuring osteoporosis using ultrasound have also been developed. One such ultrasound system measures BMD at the patient's heel and takes about a minute. The ultrasound systems for testing osteoporosis are smaller and less expensive than traditional DEXA systems. These systems have recently received US Food and Drug Administration (FDA) clearance. The hope is that this more compact, lower cost system will allow this vital diagnostic test to become more widely available in the future. By primarily measuring peripheral sites such as the heel, ultrasound densitometry may not be as sensitive as techniques such as DEXA or QCT that measure the spine or hip since the heel may be normal in bone density even when central sites such as the hip or spine are already significantly abnormal.

Further, density changes in the heel occur much slower than in the hip or spine. Therefore ultrasound densitometry should not be used to monitor a patient's response to therapy. However, the new ultrasound densitometry systems will allow many more people access to bone densitometry and potentially diagnose osteoporosis before a traumatic fracture occurs.

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:

1. Estrogen deficient women at clinical risk for osteoporosis.
2. Individuals with vertebral abnormalities.
3. Individuals receiving, or planning to receive, long-term glucocorticoids.
4. Individuals with primary hyperparathyroidism.
5. 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.

Defining Osteoporosis by BMD The World Health Organization has established the following definitions based on bone mass measurement at the spine, hip, wrist or heel:

Normal: Bone Mineral Density is within 1 Standard Deviation of a “young normal” adult (T-score at -1.0 and above)

Low bone mass (osteopenia): BMD is between 1 and 2.5 Standard Deviations below that of a “young normal” adult. (T-score between -1& -2.5)

Osteoporosis: BMD is 2.5 Standard Deviations or more below that of a “young normal” adult (T-score at or below -2.5).

T-Score:
WHO Criteria for Osteoporosis in Women
BMD > -1.0 below the young adult reference range
BMD is -1.0 to -2.5 SD below the young adult reference range
BMD < -2.5 SD below the young adult reference range
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.

MEDICAL CONDITIONS THAT MAY BE ASSOCIATED WITH AN INCREASED RISK OF OSTEOPOROSIS

AIDS/HIV, Amyloidosis, Ankylosing spondylitis, Chronic obstructive pulmonary disease, Congenital porphria, Cushing's syndrome, Eating disorders (e.g., anorexia nervosa, Female athlete triad, Gastrectomy, Gaucher's Disease, Hemochromatosis, Hemophilia, Hyperparathyroidism, Hypogonadism, primary and secondary (e.g., amenorrhea), Hypophosphatasia Idiopathic scoliosis, Inadequate diet. Inflammatory Bowel Disease Insulin-dependent diabetes mellitus Lymphoma and leukemia Malabsorption syndromes Mastocytosis Multiple myeloma Multiple sclerosis Pernicious anemia Rheumatoid arthritis Severe liver disease, especially primary biliary cirrhosis Spinal cord transsection Sprue Stroke (CVA) Thalassemia Thyrotoxicosis Tumor secretion of parathyroid hormone-related peptide Weight loss

DRUGS THAT MAY BE ASSOCIATED WITH REDUCED BONE MASS IN ADULTS Aluminum, Anticonvulsants (phenobarbital, phenytoin), Cytotoxic drugs Glucocorticosteroids and adrenocorticotropin, Gonadotropin-releasing hormone agonists, Immunosuppressants, Lithium, Long-term heparin use, Progesterone, parenteral, Supraphysiologic thyroxine doses, Tamoxifen (premenopausal use), Total parenteral nutrition