Review: Bone Mineral Densitometry
Bone Mineral Densitometry (BMD)
What is Bone Mineral Densitometry?
Osteoporosis is a disease characterized by low bone mass and deterioration of bone tissue. This leads to increased bone fragility and risk of fracture, particularly of the hip, spine and wrist. Osteoporosis is often known as "the silent thief" because bone loss occurs without symptoms. Bone densitometry measures the bone mineral content in various sites of the body, allowing a physician to diagnose osteoporosis and assess a patient's risk of suffering bone fractures.
Osteoporosis Canada recommends all postmenopausal women and men over 50 be assessed for risk factors for osteoporosis.
Major risk factors:
- Age 65 or older
- Vertebral compression fracture
- Fracture with minimal trauma after age 40
- Family history of osteoporotic fracture (especially if your mother had a hip fracture)
- Long-term (more than 3 months continuously) use of glucocorticoid therapy such as prednisone
- Medical conditions (such as celiac disease, Crohn's disease) that inhibit absorption of nutrients
- Primary hyperparathyroidism
- Tendency to fall
- Osteopenia apparent on x-ray
- Hypogonadism (low testosterone in men, loss of menstrual periods in younger women)
- Early menopause (before age 45)
Minor risk factors:
Men and Osteoporosis
- Rheumatoid arthritis
- Prolonged use of anticonvulsants
- Prolonged heparin use
- Body weight less than 57 kg (125 lbs.)
- If your present weight is more than 10% below your weight at age 25
- Low calcium intake
- Excess caffeine (consistently more than 4 cups a day of coffee, cola or some energy drinks)
- Excess alcohol (consistently more than 2 drinks a day)
- Chronic Diseases (Liver, COPD, MM, Cancer)
Osteoporosis is often considered to be a woman’s disease. Osteoporosis is less common in men than in women for a number of reasons. Men have greater peak bone mass and do not experience the accelerated bone loss women do at menopause. As well, they generally do not live as long and are less likely to fall than elderly women.
Although osteoporosis is more common in women, osteoporosis is a serious health issue for men. As with the decline of estrogen levels in women, lower testosterone levels in men can lead to an increase in bone loss. The decline is more gradual in men and is not universal. At least one in eight men over 50 has the disease.
According to a Canadian study of healthy men and women, the number of fractures of the spine is similar in men and women over the age of 50. Elderly men account for almost 30 per cent of hip fracture cases, but men are more likely to die after a hip fracture. Fractures, or broken bones, in both men and women often lead to significant physical and emotional problems. If you have had a fracture, the chances of having another one increase greatly.
It is recommended that all patients, male or female, over the age of 65 have a screening bone densitometry examination. Patients under the age of 65 should have a baseline screening study if they have 1 major, or 2 minor risk factors.
Follow-up studies are dependent on the results of the screening examination. Patients with normal bone densities are considered low risk and can only be retested every 3 years. Patients with reduced bone densities, or risk factors for osteoporosis, are considered high risk and can be retested more frequently. Recommendations for follow-up are included in our reports.
In BMD test results, the patient’s bone density is compared to the bone density of an average young adult. An actual bone density measurement in grams per cm2 is obtained. A T-score is then calculated that compares the density of the patient’s bones (spine, femoral neck, trochanter, and total femur) relative to this average. While some bone loss with aging is considered normal, making such comparisons helps determine whether the patient is losing bone more rapidly than expected.
The T-score is expressed in units referred to as standard deviations (SDs). These SD units tell us how far the patient differs (or deviates) from what is considered normal for a young adult. Below normal is always indicated with a minus (-) sign. According to World Health Organization (WHO) classifications, for postmenopausal patients over 50, a T-score below 2.5 SDs indicates osteoporosis and a score between 1 and 2.5 SDs indicates osteopenia. Normal bone density is no more than 1 SD below the young adult normal value. For female patients under 50, and all male patients, a T-score below 2.5 SDs indicates reduced bone density, with normal bone density being anything above this.
BMD test results and the WHO classifications are only part of the picture in determining the risk for fracture. In addition to the BMD results, the Radiologist will consider factors such as age, gender, fracture history, family history and glucocorticoid (steroid) use to determine the 10-year absolute fracture risk.
Tables 1 and 2 are used to determine whether the 10-year fracture risk is low, moderate or high, considering the BMD results, age and gender. Other clinical factors, particularly a fragility fracture after age 40 or glucocorticoid use for more than three months, substantially elevate the fracture risk. The presence of either of these factors will increase the 10-year risk of fracture to the next level. If both of these particular factors were present, the patient would be considered at high risk regardless of the BMD result.
Table 1 - 10-year fracture risk for women
Table 2 - 10 year fracture risk for men
Osteoporosis Canada Website: