A bone density test, commonly known as a DEXA (Dual-energy X-ray absorptiometry) scan, is a non-invasive medical procedure. It employs low-dose X-rays to measure the mineral content within bones, assessing the strength and density of a person’s skeletal structure.
What Bone Density Tests Measure
Bone density tests measure bone mineral density (BMD). This measurement is crucial for diagnosing conditions like osteoporosis, where bones become thin and brittle, increasing fracture risk. It also helps assess future fracture risk and monitors treatment effectiveness for bone-thinning conditions.
During a DEXA scan, the patient’s bone density is compared to established reference values. A T-score compares the patient’s BMD to that of a healthy young adult of the same sex, while a Z-score compares it to individuals of the same age, sex, and ethnicity. These comparisons help determine if bone density is within a healthy range or if there are signs of bone loss.
Why Bone Density Tests Don’t Directly Detect Cancer
Bone density tests are designed to measure bone mineral content, not the presence of abnormal cells or tumors. Cancer involves uncontrolled growth of abnormal cells, which DEXA scans are not equipped to identify. While certain cancers can impact bone density, a bone density test cannot distinguish these changes from those caused by other conditions like osteoporosis or metabolic bone diseases.
The test provides information about bone density, but it does not reveal the underlying cause of any observed density changes. It lacks the resolution and tissue contrast to visualize tumors or detect malignancies. Therefore, a bone density test cannot directly diagnose cancer.
How Cancer Impacts Bones
Cancer can affect bones in several ways, primarily through bone metastasis, where cancer cells spread from their original site. Common cancers that metastasize to bone include breast, prostate, lung, kidney, and thyroid cancers. Primary bone cancers, such as osteosarcoma and Ewing sarcoma, originate directly within the bone tissue.
These cancers can change bone structure. Some cancers cause bone destruction, creating osteolytic lesions. Others stimulate new bone formation, resulting in dense osteoblastic lesions. Some can cause a mixture of both. While these changes might indirectly influence bone density, a DEXA scan measures overall mineral content, not cancerous cells.
Other Diagnostic Tools for Bone Cancer
To detect bone cancer, healthcare professionals use various diagnostic methods beyond bone density tests. X-rays are often the initial imaging test, revealing structural changes or bone destruction. However, X-rays may not show early-stage cancers effectively.
More detailed imaging techniques include:
CT scans provide cross-sectional and three-dimensional images of bones and surrounding tissues. They can show tumor location, growth into soft tissues, or spread to lymph nodes.
MRI scans are particularly effective at outlining tumors and assessing spread into surrounding areas.
Bone scans (scintigraphy) involve injecting a small amount of radioactive material that accumulates in areas of increased metabolic activity, which can indicate cancer, infection, or fractures.
The definitive diagnostic method for bone cancer is a biopsy, where a tissue sample is removed from the bone and examined under a microscope by a pathologist to confirm the presence and type of cancer cells.