Biologic markers of arthritis are elements detectable in synovial fluid, serum, or urine, that may reflect the underlying degenerative joint disease. They have the potential to be highly sensitive and specific to the presence of subclinical joint disease. Accordingly, they have applications in the early diagnosis of arthritis, the close monitoring of disease progression, and the prediction of the patient's response to treatment. There are four major categories of substances being investigated as potential biologic markers of arthritis: constituents of the extracellular matrix, degradative proteolytic enzymes, cytokines, and nitric oxide. This article reviews the state of the current research in this emerging field and its potential clinical applications.
