What is the name of the test that checks for bone metastasis using a radioactive agent?

Bone Scan (Radionuclide Bone Scintigraphy)

The test that checks bones for "hot spots" after administration of a radioactive agent to rule out bone metastasis is called a bone scan, also known as skeletal scintigraphy or radionuclide bone scan. 1

Technical Details

The procedure uses technetium-99m (99mTc)-labeled bone-seeking bisphosphonate compounds, most commonly 99mTc-methylene diphosphonate (MDP) or 99mTc-hydroxymethylene diphosphonate (HMDP), as the radioactive tracer. 1, 2

• The radiotracer is administered intravenously and preferentially accumulates at sites of active bone formation through uptake by osteoblasts. 1
• Scanning is typically performed 2.5 to 4 hours after injection, when approximately 40-50% of the injected dose has localized to the skeleton. 3
• Areas of increased osteoblastic activity appear as "hot spots" on the scan, representing focal increases in tracer uptake. 1

How It Detects Metastases

Bone metastases trigger reactive new bone formation that produces focal increases in tracer uptake, often detecting lesions before bone destruction becomes visible on plain radiographs. 1

• The scan detects the metabolic reaction of bone to underlying disease rather than the tumor itself directly. 1
• This allows detection of metastases in Phase I disease, when radiographs still appear normal. 4
• Bone scan is more sensitive than plain radiographs for detecting skeletal pathology in most cancers (excluding multiple myeloma). 1

Performance Characteristics and Limitations

Sensitivity ranges from 62-100%, with the lowest sensitivity occurring in predominantly osteolytic (bone-destroying) lesions. 1, 5

• The test is highly sensitive for osteoblastic and mixed osteolytic-osteoblastic lesions (such as prostate and breast cancer metastases). 1
• It performs poorly for purely osteolytic lesions commonly found in kidney cancer, thyroid cancer, and multiple myeloma. 1, 5
• Specificity is low (48%) because many benign processes produce increased tracer uptake, including degenerative arthritis, trauma, fractures, and Paget disease. 1, 5

Critical Pitfalls to Avoid

Never rely on bone scan alone for diagnosis—abnormal findings require correlation with plain radiographs, CT, or MRI to characterize lesions and exclude benign causes. 1, 5

• The "flare phenomenon" can occur during treatment, where healing osteoblastic activity misleadingly suggests disease progression rather than response. 1, 5
• Bone scan cannot assess epidural disease, spinal cord compression, or neural foraminal involvement—critical complications requiring MRI evaluation. 5
• Plain radiographs require 50-70% bone destruction before detecting osteolytic changes, so negative radiographs do not exclude metastases in symptomatic patients. 1, 5

Modern Alternatives

PET imaging has significant advantages over bone scintigraphy, including superior diagnostic accuracy, higher spatial resolution, and shorter imaging times. 1

• FDG-PET/CT has sensitivity of 89.7% and specificity of 96.8% for detecting bone metastases. 5
• 18F-sodium fluoride PET is the most accurate osteotropic PET imaging agent, superior to 99mTc bone scintigraphy. 1
• MRI has higher sensitivity (82-100%) and specificity (73-100%) for bone marrow metastases and detects lesions before they provoke an osseous bone response. 1