A bone density test is an imaging tool that measures bone strength and thickness to assess the risk of osteoporosis; it is not used to screen for or diagnose cancer. While the test does not directly detect cancer, its results can sometimes provide information that leads to further investigation for other conditions.
The Primary Purpose of a Bone Density Test
A bone density test’s main function is to quantify bone mineral density (BMD). The most common method is the Dual-Energy X-ray Absorptiometry (DEXA) scan, which uses low-dose X-rays to measure minerals in bones, typically at the hip and spine.
The results are used to diagnose osteoporosis and its precursor, osteopenia. Your results generate a T-score, comparing your BMD to a healthy young adult, and a Z-score, comparing it to people of your age and sex. These scores help a physician calculate your risk of fracturing a bone.
Differentiating a Bone Density Test from a Bone Scan
Confusion often arises between a bone density test and a nuclear bone scan, as their purposes are distinct. A bone density test, or DEXA scan, is a quantitative measurement that answers “how much” bone mineral is present using low levels of X-ray radiation. The process usually takes 10 to 20 minutes and requires no special preparation other than avoiding calcium supplements 24 hours prior.
A nuclear bone scan, on the other hand, is a functional test designed to detect areas of high bone metabolism. For this procedure, a small, safe amount of a radioactive substance, called a tracer, is injected into a vein. This tracer accumulates in areas where bone cells are highly active, such as at the site of a fracture, infection, or a cancerous tumor. A special camera then detects the tracer, highlighting these areas of increased activity as “hot spots,” which helps physicians identify bone abnormalities.
Incidental Findings That May Suggest Further Investigation
While a bone density test does not diagnose cancer, it can occasionally reveal findings that warrant a closer look. A radiologist reviewing DEXA scan images might notice structural anomalies, such as a localized area of bone that appears unusually dense or has a lesion-like appearance. Such findings could be an indirect sign of bone metastases and would prompt a recommendation for more specific imaging.
Another way cancer can be indirectly linked to bone density results is through the effects of cancer treatments. Certain hormone therapies or chemotherapies can accelerate bone loss, and a DEXA scan can monitor this effect. This finding is a consequence of the treatment, not a direct detection of cancer by the scan itself.
Diagnostic Steps After an Atypical Result
If a bone density test shows an unexpected structural abnormality or unusually severe bone loss, a physician will order different types of imaging to determine the underlying cause.
The diagnostic process involves more detailed studies like a standard X-ray, CT scan, or MRI to provide a defined view of the bone’s structure and surrounding tissues. If cancer is suspected, a doctor may order a nuclear bone scan to check for metabolic hot spots. If these imaging tests confirm a suspicious mass, a biopsy is the definitive procedure to confirm or rule out a cancer diagnosis. A biopsy is when a small sample of bone tissue is removed for laboratory analysis.