A routine x-ray can reveal osteoporosis of the bone, which appears much thinner and lighter than normal bones. Unfortunately, by the time x-rays can detect causes of osteoporosis, at least 30% of the bone has already been lost. In addition, x-rays are not accurate indicators of bone density. The appearance of the bone on x-ray is often affected by variations in the degree of exposure of the x-ray film.
The National Osteoporosis Foundation, the American Medical Association, and other major medical organizations are recommending a dual energy x-ray absorptiometry scan (DXA, formerly known as DEXA) for diagnosing osteoporosis. DXA measures bone density in the hip and the spine. The test takes only 5 to 15 minutes to perform, uses very little radiation (less than one tenth to one hundredth the amount used on a standard chest x-ray), and is quite precise.
The bone density of the patient is then compared to the average peak bone density of young adults of same sex and race. This score is called the "T score," and it expresses the bone density in terms of the number of standard deviations (SD) below peak young adult bone mass.
- Osteoporosis is defined as bone density T score of -2.5 SD or below.
- Osteopenia (between normal and osteoporosis) is defined as bone density T score between -1 and -2.5 SD.
Who should have bone density testing?
The National Osteoporosis Foundation guidelines state that there are several groups of people who should consider DXA testing :
- All postmenopausal women below age 65 who have risk factors for osteoporosis;
- All women aged 65 and older;
- Postmenopausal women with fractures, although this is not mandatory because treatment may well be started regardless of bone density;
- Women with medical conditions associated with causes of osteoporosis. These diseases number more than 50. A primary care physician can scan a patient's list of medical illnesses to verify that one of these conditions is not present;
- Women whose decision to use medication might be aided by bone density testing.
The National Osteoporosis Foundation guidelines state that bone density testing does not need to be performed if a person has a known osteoporotic fracture because the condition will be treated with or without bone density results. In addition, bone density testing is not appropriate if the person undergoing the test is not willing to take any treatment based on the results. Therefore, if bone density testing is done, it should be performed on people willing to take some specific action based on the results.
Sources medicinenet.com
