Utilizing DXA scans to diagnose bone loss and offer the latest treatments
More than 43 million Americans have low bone density, or osteopenia.1 Osteoporosis, a more severe case of bone loss, is a bone disease that occurs when bone mineral density (BMD) decreases, or when there are changes to the structure and strength of bone. Osteoporosis is a silent disorder that affects 10.2 million Americans, two million of whom are men.1
Because of the risk of fracture, increased mortality and morbidity rates, and costs associated with fractures, screening is necessary to diagnose low BMD early. When low bone density and osteoporosis are diagnosed early, treatment can be initiated to prevent future complications. Therefore, it is important that patients at risk are screened for low bone density.
Types of osteoporosis
Type 1 primary osteoporosis is known as post-menopausal osteoporosis. Estrogen, a hormone that modulates bone remodeling, sees levels decrease during menopause. When estrogen levels are low, bone is resorbed at a faster rate than when it is formed. This causes a decrease in bone density, mainly in trabecular bone.
Type 2 primary osteoporosis is known as senile osteoporosis and occurs in both men and women aged 70 and older. With increasing age, bone stromal cells differentiate into adipocytes, impacting the incidence of senile osteoporosis.2 Cortical thinning, along with loss of trabecular bone, is seen in type 2 primary osteoporosis.
When a patient has low bone density, secondary causes of osteoporosis should be ruled out. Secondary osteoporosis can be related to demographics, an underlying medical condition, use of certain pharmaceuticals and lifestyle factors. Many medical conditions may also contribute to low bone density, including anorexia nervosa, rheumatoid arthritis, ankylosing spondylitis, diabetes, malabsorption due to Crohn’s or celiac disease, hyperparathyroidism and scoliosis.
According to Sözen, et al., the following studies are necessary to rule out secondary osteoporosis:3
- Complete blood count (CBC)
- Serum creatinine, calcium, phosphorus and magnesium
- Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (AP)
- Thyroid-stimulating hormone (TSH) and free T4
- Vitamin D (V-D) (25 (OH) D)
- Parathyroid hormone (PTH)
- Total testosterone and gonadotropin in younger men
- BTMs (bone turnover markers)
Other contributing factors
There is a greater prevalence of osteoporosis in Caucasian and Asian women, while Hispanic and Black women have a lower incidence. In late perimenopause and early postmenopause, bone density decreases due to a reduction in estrogen, which causes a decrease in bone formation.
Medications such as glucocorticoids, loop diuretics and some chemotherapeutic agents can contribute to bone loss.4 Taking five milligrams of a glucocorticoid (prednisone) per day for more than three months increases the risk of osteoporosis. High doses or long-term use of proton pump inhibitors like esomeprazole, lansoprazole, and omeprazole decrease calcium absorption, which can lead to osteoporosis.
Lifestyle factors that contribute to low bone density are smoking tobacco, body weight less than 127 pounds and living a sedentary lifestyle. Because of decreased calcium absorption, having more than three units of alcohol per day, more than three servings of caffeine per day or greater than 2,300 milligrams of sodium per day will also increase the risk of developing osteoporosis.5
Warning signs of osteoporosis
Because osteoporosis is a silent condition, fragility fractures may be the first warning sign. As bone density decreases, the risk of fragility fractures increases. Fragility fractures occur with a small trauma that would not typically cause a fracture.
Examples include sustaining a fracture after falling from a standing height or lower, fracturing a rib while coughing or sneezing, or a vertebral compression fracture. Two-thirds of all vertebral compression fractures are asymptomatic5 and, if severe enough, will produce a loss of height. Therefore, it is important to measure a patient’s height frequently.
Fragility fractures affect an estimated 1.5 million Americans each year6 and significantly increase morbidity and mortality rates. Therefore, when a fragility fracture occurs, a DXA scan must be performed to determine the BMD.
Dual-energy X-ray absorptiometry (DXA) is the gold standard used to diagnose osteoporosis and other conditions related to low BMD. DXA uses low- and high-energy X-ray beams to differentiate bone from soft tissue.
Women aged 65+ and men aged 70+ should be screened biannually for osteoporosis. However, anyone younger than this who displays risk factors for osteoporosis should have their bone density measured using DXA. Patients at risk for osteoporosis should be screened biannually. In addition, if a patient is undergoing treatment for low bone density or osteoporosis, they should be scanned more frequently.
To diagnosis osteoporosis using the DXA, the lumbar spine and proximal femur can be scanned. If the lumbar spine or proximal hips have fractures, surgical hardware or advanced osteophyte formation, the forearm should be scanned. The forearm is the preferred site to scan patients with primary hyperparathyroidism because the loss of cortical bone will be detected in the distal radius.
When a patient is scanned using DXA, a T-score or Z-score is calculated to indicate their BMD. The T-score compares the patient’s BMD to a healthy 30-year-old the same sex as the patient and is used for postmenopausal women and men aged 50 and older. The Z-score was established using data from thousands of women aged 20-80 years. It compares the patient’s BMD to people of the same sex, age and ethnicity and is used for premenopausal women and men less than 50 years of age.
Additional DXA uses:
- Vertebral Fracture Assessment (VFA) is a scan from T4 to L5 in a lateral position, evaluating vertebral fractures.
- Fracture Risk Assessment, or FRAX, predicts the 10-year fracture risk using the patient’s risk factors, femoral BMD or T-score. FRAX cannot be calculated if the patient is on pharmaceutical therapy for osteoporosis.
- Trabecular Bone Score (TBS) is a measure of the micro texture of bone. Fracture prediction improves when both TBS and FRAX are utilized.
- Body composition scans differentiate bone, muscle, fat and skin, and are indicated for patients with HIV, anorexia nervosa, sarcopenia and those undergoing bariatric surgery. Measuring body composition is also gaining popularity with athletes. The body composition scan is good for providing information about physical fitness but is not used to diagnose low bone density or osteoporosis.
Preparing patients for a DXA scan
To prepare for a DXA scan, patients should avoid calcium supplements, multivitamins or antacids containing calcium for at least 24 hours before the scan. The patient should wear loose-fitting clothing free of metal, including zippers, snaps and buttons. All jewelry and any bras with underwire must be removed.
Some important things to note:
- If a patient is undergoing a procedure or study using intravenous or oral contrast, such as barium or iodine, the DXA scan should be postponed for one week to ensure there is no residual contrast that would interfere with an accurate bone density study. This is also true for studies using radiopharmaceuticals, such as a Technetium-99 bone scan or an Iodine-131 thyroid scan.
- The DXA report from one facility cannot be accurately compared to another facility’s report. Therefore, it is important to have all DXA scans performed at the same facility. This is especially true when monitoring the effectiveness of treatment for low bone density or osteoporosis.
After a patient undergoes a DXA scan, a report will be generated that includes the BMD in g/cm2 and the patient’s T-score. This will determine if preventative or therapeutic intervention is needed. According to Qadir, et al., pharmaceutical therapy should be initiated when:2
- the lumbar spine, femoral neck or hip T-score is -2.5 or less
- the femoral neck or total hip T-score is between -1.0 and -2.5, with a 10-year hip fracture risk of 3% or a 10-year 20% risk of osteoporotic fracture
To prevent fragility fractures, pharmaceutical therapies can be initiated. Medication options include:
- Bisphosphonates: slow the process of bone resorption.
- Calcitonin: restricts activity of osteoclasts within bone.
- Selective Estrogen Receptor Modulators (SERM): prevent bone loss by imitating natural estrogen.
- Hormone replacement therapy (estrogen): used for women who undergo early menopause to minimize bone loss.
- Teriparatide: imitates natural parathyroid hormone.
- RANKL Inhibitor: reduces osteoclast activity and bone resorption.
- Denosumab (Prolia): monoclonal antibody.
To maintain healthy bone density and reduce the risk for osteoporosis, proper nutrition and exercise play an important role.
Proper nutrition, including getting enough calcium and vitamin D, contributes to healthy bones. This can be accomplished by taking supplements or eating more calcium-rich dairy products and increasing exposure to sunlight. Weight-bearing and resistance exercises are effective at building bone during formative years and maintaining bone density after it has peaked. It is also advisable to eliminate smoking, reduce alcohol intake to less than three units per day, have no more than three servings of caffeine per day and consume no more than 2,300 milligrams of sodium per day.5
It is important to be aware of warning signs and symptoms when it comes to low bone density. Incorporating consistent DXA scanning into treatment plans for aging patients can help them avoid fractures that can lead to even more health complications.
CHERYL BURTLE, DC, RT(R)(ARRT), is an assistant professor at Logan University and a lead instructor in Foundation of Diagnostic Imaging (X-ray physics) and Radiographic Positioning. Learn more at logan.edu/faculty/cheryl-burtle-dc-rtrarrt.
- Wright NC, Looker AC, Saag KG, Curtis JR, Delzell ES, Randall S, Dawson-Hughes B. The recent prevalence of osteoporosis and low bone mass in the United States based on bone mineral density at the femoral neck or lumbar spine. J Bone Miner Res. 2014 Nov;29(11):2520-6. doi: 10.1002/jbmr.2269. PMID: 24771492; PMCID: PMC4757905.
- Qadir A, Liang S, Wu Z, Chen Z, Hu L, Qian A. Senile Osteoporosis: The Involvement of Differentiation and Senescence of Bone Marrow Stromal Cells. Int J Mol Sci. 2020 Jan 5;21(1):349. doi: 10.3390/ijms21010349. PMID: 31948061; PMCID: PMC6981793.
- Sözen T, Özışık L, Başaran NÇ. An overview and management of osteoporosis. Eur J Rheumatol. 2017 Mar;4(1):46-56. doi: 10.5152/eurjrheum.2016.048. Epub 2016 Dec 30. PMID: 28293453; PMCID: PMC5335887.
- Guise TA. Bone loss and fracture risk associated with cancer therapy. Oncologist. 2006 Nov-Dec;11(10):1121-31. doi: 10.1634/theoncologist.11-10-1121. PMID: 17110632.
- Berry, M. Bone Densitometry Basics: Module 4- Treatment and Prevention. ASRT.org, 2017. https://asrt.mycrowdwisdom.com/diweb/catalog/item/id/6448844/q/t=6479&c=40
- Clynes MA, Harvey NC, Curtis EM, Fuggle NR, Dennison EM, Cooper C. The epidemiology of osteoporosis. Br Med Bull. 2020 May 15;133(1):105-117. doi: 10.1093/bmb/ldaa005. PMID: 32282039; PMCID: PMC7115830.