Radiographs of the painful area should be obtained, although radiographic signs are often minimal early in the infection. The earliest radiographic evidence of acute hematogenous osteomyelitis is swelling of soft tissue adjacent to the bone; within a few days of onset, lysis in the metaphyseal region becomes visible. Periosteal elevation with its new bone formation and the creation of sequestra become obvious on radiographs after a couple of weeks. A technetium-99m bone scan is an extremely sensitive test for identification of areas of inflammation in the bone. However, the test is not particularly specific to bone infection, because it is also positive after fracture or any other condition that irritates the periosteum and causes new bone formation. Magnetic resonance imaging will reveal edema or inflammation or show a collection of pus if present in the bone.

Recently, radioactively labeled leukocytes have been used to diagnose a focus of osteomyelitis. In this technique, a blood sample is drawn from the patient; the leukocyte cells are cultured and labeled with radioactive indium-111 and then reinjected into the patient. As leukocytes tend to accumulate at a focus of infection, the indium-labeled leukocytes also tend to focus in the infected area. The radioactivity can be identified on a scan performed 24 to 72 hours after reinjection.