To Scan or Not to Scan? DXA in Postmenopausal Women
Kristi Tough DeSapri, MD, CCD, NCMP and Rachel Brook, MD
Cleveland Clinic Journal of Medicine April 2020, 87 (4) 205-210; DOI: https://doi.org/10.3949/ccjm.8...
Fracture is a major cause of morbidity and death in postmenopausal women. Dual-energy x-ray absorptiometry (DXA) measures bone mineral density, which helps in estimating fracture risk and in identifying those who may benefit from treatment. Although screening guidelines differ somewhat for postmenopausal women under age 65, in general, DXA is indicated if the patient has a high risk for fracture.
- Bone is lost with aging and declining estrogen and testosterone levels, particularly after menopause.
- Advanced age, prior fragility fracture, and low T scores (< –3.0) are the greatest risks factors for fracture.
- DXA is considered the therapeutic standard for measuring bone mineral density.
- In younger postmenopausal women, guidelines recommend DXA only in those who have a substantial risk of fracture based on clinical factors.
A 56-year-old woman presents for a routine physical examination. Her last menstrual period was at age 51. She takes hydrochlorothiazide for hypertension and a multivitamin containing 400 mg of calcium carbonate plus 1,000 IU vitamin D3 daily. On most days, she eats 2 servings of calcium-rich foods (6 oz yogurt and 1 or 2 servings of cheese). She has no personal or family history of osteoporosis or fracture. She exercises 3 times a week and has had no falls or imbalance. She drinks about 5 alcoholic beverages per week. Her weight is 140 lb (63.5 kg) and height is 5 ft 2 in (157.5 cm), giving her a body mass index of 25.6 kg/m2, stable from last year. She asks whether she should get a dual-energy x-ray absorptiometry (DXA) scan to check her bone mineral density (BMD) because many of her postmenopausal friends have done so.
Is DXA screening indicated in this patient?
BONE MINERAL DENSITY DECLINES WITH AGE AND MENOPAUSE
Most women achieve peak bone mass in their second or third decade of life, depending on skeletal site, with the most active bone formation occurring during childhood, adolescence, and young adulthood. Bone is lost with age and with declining levels of estrogen and testosterone, particularly after menopause, and low bone mineral density is associated with an increased risk of fracture.
Estrogen plays a key role in maintaining the balance between bone formation and resorption. Estrogen deficiency disrupts this balance, resulting in decreased bone formation and increased bone resorption.
The Study of Women Across Nations found that women may lose 5% to 10% of bone mineral density in both cortical and trabecular bones during late perimenopause and the first postmenopausal years.1 As women age, this bone loss slows but continues at an average rate of about 0.5% to 1% per year.
Women with premature ovarian insufficiency or early menopause from natural or surgical causes experience more profound bone loss and are at higher risk of fracture during their life.2
Several other medical, genetic, and surgical conditions also either decrease peak bone mass or accelerate bone loss. These include medications such as glucocorticoids (> 5 mg for > 3 months) and lifestyle factors such as smoking and being underweight (ie, body mass index < 18 kg/m2). Rheumatoid arthritis and diabetes, particularly type 1 diabetes, also contribute to bone loss and increase the risk of fracture.3
The National Osteoporosis Foundation has published an extensive list of risk factors that can be shared with patients.4 Advancing age, prior fragility fracture, and a T score below –3.0 are the strongest risk factors predicting future fracture.
OSTEOPOROSIS IS COMMON
According to data from the third National Health and Nutrition Examination Survey, more than 9.9 million Americans have osteoporosis (defined as a T score ≤ −2.5), and an additional 43.1 million have osteopenia (a T score between −1.0 and −2.5), leading to more than 2 million fractures per year.5,6 These osteoporosis-related fractures are a major cause of morbidity and death in postmenopausal women.
DXA measures a patient’s bone mineral density. Other screening tools exist, but DXA is considered the technical standard. Results are reported in absolute terms in g/cm2 and also as a T score (the difference, in standard deviations, between the patient’s value and the mean value for healthy 30-year-olds of the same sex) and a Z score (the difference between the patient’s value and the mean value of people the same age, race, and sex).
The clinical purpose of a DXA scan is to screen patients for low bone mass and osteoporosis. It also provides a surrogate measure of bone strength to help estimate fracture risk.
For example, a 10% loss of bone mass (equivalent to a 1 standard deviation decrease in the T score) in the vertebrae can double the risk of vertebral fractures. In the hip, a 10% loss of bone mass can cause a 2.5 times greater risk of hip fracture.7,8
For DXA to be an appropriate screening test, it must be able to detect disease (osteoporosis or osteopenia) at a stage when treatment (medication or lifestyle modification) can effectively reduce the serious consequences of the disease (eg, fracture). It must also be safe (this applies to both the test and the treatment), widely available, and inexpensive.
RECOMMENDATIONS FOR DXA SCREENING IN POSTMENOPAUSAL WOMEN
Several major medical societies strongly recommend DXA testing for women age 65 and older,3,9,10 but the recommendations are not as clear for younger postmenopausal women, such as our patient. In general, however, women under age 65 should be screened if they have clinical risk factors for bone loss or fracture.
The US Preventive Services Task Force (USPSTF)9 recommends DXA of the hip and spine if the 10-year predicted risk of major osteoporotic fracture according to the Fracture Risk Assessment Tool (FRAX)11 without bone mineral density is 8.4% or greater. This is equal to the fracture risk of a 65-year-old white woman of mean height and weight without major risk factors for fracture.
The National Osteoporosis Foundation4 and the International Society of Clinical Densitometry10 both recommend DXA for postmenopausal women under age 65 and those in the menopausal transition who have clinical risk factors for fracture such as:
- Low body weight
- Prior fracture
- A disease or condition associated with bone loss
- Use of medications that cause bone loss, such as glucocorticoids.
DXA is also recommended in women being considered for pharmacologic treatment and to monitor treatment response.