Determinants of synovial fluid lactate concentration.

The resting intraarticular pressure and the type of arthropathy [rheumatoid arthritis (RA) or non-RA] have been examined for their importance as determinants of synovial fluid (SF) lactate concentration in patients with knee effusions. SF lactate concentration was higher in RA than in non-RA knees. This difference was not related to the resting intraarticular pressure at the time of sampling. After drainage of SF and saline lavage of the joint, the rate of increase of lactate in a fixed volume of intraarticular saline was examined under resting conditions. The rate of increase of the lactate concentration was significantly greater in RA joints. It is most likely that SF lactate concentration under resting conditions will reflect the lactate concentration during the preceding period of activity which, in turn, is probably a composite function of the extent of synovial hypoxia due to hypoperfusion and the type of arthropathy.