Measurement of bone mass

Published on 02/03/2015 by admin

Filed under Endocrinology, Diabetes and Metabolism

Last modified 02/03/2015

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CHAPTER 10

Measurement of bone mass

1. Why measure bone mass?

Bone mass, measured by bone mineral densitometry, is used to establish the diagnosis of osteoporosis, to predict the risk of subsequent fractures, and to monitor changes in bone mass during therapy for osteoporosis. No clinical finding, laboratory test, or other radiographic examination is able to reliably identify individuals with osteoporosis. Conventional radiographic techniques are not sensitive enough to diagnose osteoporosis as they do not reliably detect bone loss until 30% to 40% of bone mineral is lost. Although bone densitometry may determine low bone mass, it cannot identify the etiology of the bone loss. Thus, bone densitometry must be used with a complete clinical evaluation, laboratory testing, and other diagnostic studies to determine the cause of and the most appropriate treatment for osteoporosis.

2. Is bone mass the only parameter that determines whether a bone will fracture?

3. How does bone densitometry measure bone mass?

4. What techniques are available to measure bone mass?

5. What is the preferred method for measuring bone mass?

6. What are the indications for the measurement of bone mass?

Widespread BMD screening for osteoporosis is not recommended at this time. The United States Preventive Services Task Force (USPSTF) has recommended screening for osteoporosis of women of all racial and ethnic groups age 65 or greater and in women 50 to 65 years of age whose 10-year risk for any osteoporotic fracture is 9.3% or greater (determined by the FRAX fracture assessment tool; see later). The USPSTF concluded that for men, evidence of the benefits of screening for osteoporosis is lacking and the balance of benefits and harms cannot be determined.

The National Osteoporosis Foundation (NOF) recommends BMD testing for the following:

image Women age 65 and older and men age 70 and older regardless of clinical risk factors

image Younger postmenopausal women and men age 50 to 69 for whom there is concern about the patient’s clinical risk factor profile

image Women in the menopausal transition if there is a specific risk factor associated with increased fracture risk, such as low body weight, prior low-trauma fracture, or high-risk medication

image Adults who have a fracture after age 50

image Adults who have a condition (e.g., rheumatoid arthritis) or are taking a medication (e.g., glucocorticoids in a daily dose ≥ 5 mg prednisone or equivalent for ≥ 3 months) associated with low bone mass or bone loss

image Anyone being considered for pharmacologic therapy for osteoporosis

image Anyone being treated for osteoporosis, to monitor treatment effect

image Anyone not receiving therapy in whom evidence of bone loss would lead to treatment

Postmenopausal women who are discontinuing estrogen should be considered for bone density testing.

In addition, DXA is also being increasingly used to study bone status in pediatric and adolescent patients, to perform vertebral fracture assessment, and to determine body composition.

7. What do bone mass measurements mean?

8. What are T-scores?

9. What do Z-scores tell us about the patient?

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