Besides synovial fluid examination, radionuclide joint scanning is a procedure that may offer useful information. For screening purposes, the scan could be performed with one of the isotope-labeled phosphate compounds used for bone scanning. These scans reveal abnormality in most joints that have a significant degree of inflammation, even when subclinical. Joint scanning permits a reasonably accurate assessment of the number, location, and degree of activity of involved joints and offers an objective (although only semiquantitative) method for evaluating results of therapy. Although fairly sensitive, the phosphate agents are not ideal for joint scanning, since increased concentration denotes increased activity of bone osteoblasts in response to adjacent synovial abnormality rather than a primary synovial reaction. Other etiologies for osteoblastic stimulation, such as osteochondritis dissecans, traumatic joint disease, active osteoarthritis, healing fractures, and the later stages of aseptic necrosis, may all produce abnormal bone scan images, which sometimes are hard to differentiate from arthritis. In such cases other compounds may be employed, including technetium pertechnetate or labeled albumin. These tend to remain in blood vessels, thereby indicating regions of increased vascularity or hyperemia such as the synovial membrane when involved by active arthritis. These compounds are a little less sensitive than the phosphates but are more specific for synovial disease.