The goals with testing are to determine whether a person has osteoporosis, has low bone mass and an increased risk of developing the disease, is menopausal and/or hormone-deficient, and/or has an underlying condition that may be causing or exacerbating bone loss. Testing may be done to screen for bone density loss or to evaluate bone status when a person has an unexpected bone fracture and may be used to monitor osteoporosis therapy for effectiveness. Diagnostic imaging, a non-laboratory test, is used in the Bone Mineral Density test, the primary screening and diagnostic test for osteoporosis.
Several organizations have published guidelines on screening for osteoporosis, including the American College of Obstetricians and Gynecologists (ACOG), National Osteoporosis Foundation (NOF), and the U.S. Preventive Services Task Force (USPSTF), which recommend screening for all women beginning at age 65 and, in some cases, younger women based on risk factors. The NOF also recommends screening men age 70 and older as well as those age 50 to 69 with risk factors.
The bone mineral density (BMD) test is the primary test used to identify osteoporosis and low bone mass. One of the preferred and most accurate ways to measure BMD is Dexa-Scan (dual-energy X-ray absorptiometry or DXA). It uses a low energy X-ray to evaluate bone density in the hip and/or spine. BMD is often reported in terms of peak bone mass in young adults. A BMD value that is less than 1 standard deviation below the young adult mean is considered normal. BMD in osteopenia has a value between -1 and -2.5 standard deviations below the young adult mean while osteoporosis BMD values are even lower and are at least -2.5 standard deviations below the mean.
Your health care provider can now also use a calculator, called the FRAX tool, to better determine your risk of a hip, wrist, shoulder, or spine fracture after age 40. Available online or on paper, the calculator, developed by the World Health Organization, considers a person's bone mineral density measurement and a number of other risk factors. It is an algorithm for estimating 10-year probability of fracture. The NOF has adapted this algorithm for the U.S. and its Clinician's Guide released in February 2008 applies it.
Portable BMD screening devices, utilized at some pharmacies, health fairs, etc., are used to scan people’s heels or fingers. These scans are not as accurate as the DXA but may be used as an initial scan. When these tests show decreased bone density, a DXA scan may be performed for confirmation.
Other diagnostic imaging tests that may be done to measure BMD and to detect osteoporosis include CT scans (computerized tomography), X-rays, and ultrasounds. A general screening test called "body composition analysis" can determine a person's percentages of body weight due to muscle, fat, bone, and water. There are a few different ways to measure body composition including the use of specialized instruments. If body composition analysis is performed and results tracked from year to year, it may be able to help detect bone loss.
One other diagnostic imaging test used to evaluate the condition of the bones is a bone scan, which is not to be confused with the bone density scan or BMD. While the BMD test is used to identify low bone density that is indicative of osteoporosis and is non-invasive, a bone scan is a nuclear medicine test used to rule out other serious conditions of the bones. To perform this test, a radioactive tracer is injected into a vein in the arm. The tracer then travels through the blood and is absorbed by the bones. The level of radioactivity detected in the bone is evaluated and can point to conditions or diseases such as metastatic cancer, infection, causes of unexplained bone pain, or Paget's disease. This type of scan can discover problems with the bones much earlier than a regular X-ray and may be ordered when someone has a high frequency of bone fractures.
Blood tests that may be ordered include:
- Blood calcium levels - this test is usually normal in osteoporosis but may be elevated with other bone diseases.
- Vitamin D - deficiencies can lead to decreased calcium absorption
- Thyroid tests - such as T4 and TSH to screen for thyroid disease
- Parathyroid hormone (PTH) - to check for hyperparathyroidism
- Follicle-stimulating hormone (FSH) - to check for menopause
- Testosterone - to check for deficiency in men
- Protein electrophoresis - to identify abnormal proteins produced by a certain type of cancer (called multiple myeloma) that can break down bone
- Alkaline phosphatase (ALP) - to test for increased levels that may point to a problem with the bones
Tests measuring bone loss
Bone resorption tests tell about the rate of bone loss. They can be checked before treatment and again after treatment to see if the rate of bone loss has decreased. They include:
- C-telopeptide (C-terminal telopeptide of type 1 collagen (CTx))
- Urinary collagen type 1 cross-linked N-telopeptide (NTX)
- Deoxypyridinoline (DPD)
- Pyridinium Crosslinks
- Urinary hydroxyproline
- Tartrate-resistant acid phosphatase (TRAP) 5b
- Bone sialoprotein (BSP)
Tests measuring bone formation
Bone formation tests tell about the rate of bone production. As with bone turnover tests, they may be checked before the start of treatment and periodically after treatment to see if bone formation has increased. They include:
- Bone-specific alkaline phosphatase (ALP)
- Osteocalcin (bone gla protein)
- P1NP (Procollagen Type 1 N-Terminal Propeptide) and C-terminal (C1NP)
For more detailed information on these tests, see the article on Bone Markers.