What is the primary indication for a bone scan?

A bone scan is primarily indicated for evaluating conditions associated with abnormalities in bone metabolism. The key uses of a bone scan include the assessment of delayed fractures, which may not show clear abnormalities on plain radiographs initially, and the detection of osteomyelitis, an infection of the bone that can also be subtle on initial imaging. A bone scan utilizes a radiolabeled tracer that binds to areas of increased bone activity, making it particularly useful for identifying areas of inflammation or infection, as well as metastatic disease that may show increased uptake in bone.

The other options do not align with the primary purpose of a bone scan. Gall bladder stones are evaluated via ultrasound or CT imaging, adrenal tumors are assessed by imaging modalities like CT or MRI, and pulmonary embolism is typically diagnosed using CT pulmonary angiography or ventilation-perfusion scans. Hence, the use of a bone scan specifically addresses the evaluation of bone issues and related metabolic changes, confirming that it is the best choice for this question.