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BLOG: Modalities used to diagnose osteoporosis
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This installment of osteoporosis primer for PAs will focus on the modalities used to diagnosis osteoporosis. To reiterate a diagnosis of osteoporosis could be made in an adult patient aged older than 50 years who has experienced a ground level fall resulting in a fragility hip or vertebral compression fracture. Vertebral compression fractures are the most common fragility type fracture but clearly the fracture associated with the highest mortality are those of the hip. In fact, any fracture, excluding toes, fingers and skull, can be considered osteoporotic fragility type if they occur from a fall from ground level or less. However, follow-up bone density testing for these patients is indicated. These fractures cause substantial pain, disability and decreased quality of life. Besides the increased morbidity that these fractures cause, they are also expensive to the health care system resulting in 2.5 million medical visits and over 400,000 hospital admissions per year.
Osteoporosis causes most fragility fractures and is the most common disease of bone. It is associated with low bone mass and micro architectural deterioration of bone tissue that results in increased bone fragility and fracture risk. The gold standard for the diagnosis of osteoporosis is bone density testing using dual energy X-ray absorptiometry, or DXA. A DXA scan is a noninvasive imaging test that takes usually less than 20 minutes and is less radiation than a chest x-ray.
The World Health Organization international reference standard for osteoporosis diagnosis is a T-score of –2.5 or less at the femoral neck. The diagnosis of osteoporosis is reserved for postmenopausal women and men aged 50 and older. Women prior to menopause and men younger than 50 with a z score less than –2.0 may be defined as “below the expected range for age” but cannot be diagnosed as osteoporotic. A normal T-score is considered anything higher than –1.0 standard deviations from the normal reference standard. The normal reference standard is the bone density of a 30-year-old white woman. Osteopenia, or more preferably low bone mass, is defined as a T-score between –1.0 and –2.5 standard deviations from the reference. Ideally T-score is obtained from 1 hip, femoral neck and the lumbar spine. However, in patients who have had prior hip fractures with hardware, lumbar spine surgeries, and degenerative changes in the lumbar spine the one-third radius may be used as a testing site on DXA imaging.
Bone mineral density testing via a DXA scan is indicated for women aged 65 years and older, and men aged 70 years and older. Postmenopausal women younger than 65 are indicated if they have risk factors for low bone mass including history of prior adult age fracture, low body weight, high risk medication use such as glucocorticoid use, and other diseases associated with bone loss. However, indications also include high risk peri-menopausal women, any adult who experiences a fragility fracture and any adult who suffers from a disease or condition associated with low bone mass or bone loss.
Bone mineral density testing via DXA is usually repeated every 1 to 2 years depending on the patient's risk factors and whether they have been started on osteoporosis pharmacotherapy. Some limitations of bone mineral density testing via DXA is that it is technician and clinician dependent as there can be optimal and suboptimal images and interpretations; patients ideally should have DXA on the same machine by the same technician and read by the same densitometrist and this may not be practical; and patients with hyperparathyroidisim and very obese patients are limited to forearm bone mineral density testing.
FRAX is a WHO-sponsored, country-specific tool that uses bone mineral density at the femoral neck with a set of well validated clinical risk factors for fractures that are largely independent of bone mineral density, such as family history of hip fractures, personal history of adult age fracture, use of glucocorticoids greater than 3 months, and use of alcohol and tobacco, and others. A diagnosis of osteoporosis can be made if the T-score is between –1.0 and –2.5 and the 10-year probability of hip fracture is greater than or equal to 3% or if the 10 year probability of major osteoporotic fracture is greater than or equal to 20%.
FRAX may also be used without bone mineral density testing for high risk patients aged between 50 and 65 years. If you are assessing a patient in that age range, you can perform a FRAX tool and if the 10-year probability of an osteoporotic fracture is greater than or equal to 9.3%, a follow-up DXA scan is indicated. Some of the limitations of FRAX tool is that it does not account for history of falls, does not quantify dosage risk of corticosteroid use, and is not valid for patients who have begun osteoporosis pharmacotherapy.
There are several risk assessment tools that may be used in the absence of DXA scan and FRAX, such as quantitative computed tomography (QCT), trabecular bone score (TBS) and quantitative ultrasound densitometry. These are less common modalities, however. More commonly vertebral imaging is used. To reiterate, a vertebral fracture is diagnostic of osteoporosis, with or without bone mineral density testing. Vertebral lateral images of the thoracic and lumbar spine is indicated for women aged 70 and older and men aged 80 and older if the T-score is than or equal to –1.0, women aged 65 to 69 and men aged 70 to 79 with a T-score less than or equal to –1.5, and postmenopausal women and men aged 50 and older with certain risk factors, such as historical height loss. However, vertebral imaging may be considered for any patient in this age cohort. This test may be repeated if new documented height loss, new back pain occurs or if someone is being considered for a drug holiday.
Key takeaways for PAs:
Osteoporosis may be diagnosed by fracture alone, specifically low energy hip and vertebral fractures;
Understand the indications for DXA testing and how to diagnose osteoporosis via T-score;
Use the FRAX tool with or without bone mineral density to determine patients at risk for fractures; and
Vertebral imaging may be used in the absence of DXA to screen for osteoporosis in high risk patients.
Daniel J. Acevedo, PA-C, is a nationally certified physician assistant and the lead advanced practice provider at OrthoVirginia in Lynchburg, Virginia. His interests include physician assistant education and osteoporosis.