It images OSTEOBLASTIC RESPONSE, not tumour — so a purely lytic deposit can be invisible, and a healing fracture can look identical to a metastasis.

Bone scintigraphy shows osteoblastic activity, which is the bone's RESPONSE to a process, not the process itself. That single fact explains both its sensitivity and every one of its pitfalls.
PURELY LYTIC disease — classically myeloma, and some renal and thyroid metastases — provokes little osteoblastic response and can be scan-negative. A negative bone scan does not exclude skeletal metastases in those tumours.
DISTRIBUTION is what separates metastases from degenerative and traumatic uptake: metastases are typically random, asymmetric and axial; degenerative change is symmetric and periarticular; rib fractures line up in a linear, contiguous pattern.
A SUPERSCAN — intense skeletal uptake with faint or absent renal and soft-tissue activity — indicates diffuse metastatic disease or metabolic bone disease, and is easily misread as a normal, high-quality scan.
FLARE after starting treatment shows increased uptake in healing lesions and can be mistaken for progression; the timing is what distinguishes it.

Confirm the tracer, injected activity and the delay before imaging — the standard delay allows soft-tissue clearance, and imaging too early degrades target-to-background.
Obtain whole-body anterior and posterior images; add SPECT or hybrid imaging for equivocal findings, particularly in the spine.
A three-phase study (flow, blood pool, delayed) is what separates osteomyelitis from cellulitis and assesses a painful prosthesis.
Ensure the bladder is emptied before imaging the pelvis — bladder activity obscures the sacrum and pubis.
Check for injection-site extravasation, which can mimic a lesion and reduce the delivered dose.

Assess technical quality first: tracer distribution, renal and bladder activity, and any extravasation.
Look at the OVERALL pattern before any single focus — specifically ask whether this is a superscan.
Assess the axial skeleton systematically: skull, spine, ribs, pelvis, then the appendicular skeleton.
For each focus, describe its site, intensity and whether it is symmetric.
Classify the pattern: random and asymmetric, periarticular and symmetric, or linear and contiguous along ribs.
Correlate every equivocal focus with a radiograph or cross-sectional imaging before calling it a metastasis.
Assess the kidneys and soft tissues for incidental uptake.
State the clinical context — recent trauma, surgery, treatment start — since it changes the reading of the same picture.

Multiple randomly distributed asymmetric foci in the axial skeleton, in a patient with a known primary, indicate metastases.
A three-phase study positive in all three phases in the same location supports osteomyelitis.

⚠️ A NEGATIVE BONE SCAN DOES NOT EXCLUDE SKELETAL METASTASES, particularly in myeloma and in purely lytic disease. Say so explicitly rather than reporting no metastases.
A superscan can be misread as normal — the absent renal activity is the tell, and its absence must be actively checked.
Solitary uptake is frequently benign; it should be correlated rather than reported as a metastasis.

Reading a bone scan

Reference values