A comparison of normal and pathological synovial fluid.

Synovial fluid from 16 normal subjects was compared with that from 149 patients with a variety of rheumatic disorders. Normal fluid had fewer cells and a lower content of beta-glucuronidase than osteoarthritic samples. Particles, including occasional birefringent crystals, were seen in normal fluids as well as pathological samples. Alizarin red staining particles (presumed to contain apatite) were seen in all diagnostic groups; their numbers showed some correlation with radiological calcification in and around the joints and with a hypertrophic subchondral bone response. Lactate levels were highest in septic arthritis. No assay showed disease specificity.