Lactate dehydrogenase activity and its isoenzymes in serum and synovial fluid of patients with rheumatoid arthritis and osteoarthritis.

By determining the total activity of total lactate dehydrogenase (LDH-T) and its isoenzymes in serum and synovial fluid (SF) of patients with rheumatoid arthritis (RA) and osteo-arthritis (OA) we demonstrated in RA serum increased (p less than 0.02) activity of hepatic LDH (LDH-H) and a shift of the LDH isoenzymatic profile towards the M forms; in rheumatoid SF increased (p less than 0.001) activity of the total LDH-T and LDH-H which makes possible the use of these markers of inflammation in assessing RA activity. Values for LDH-T and LDH-H of 400-700 U/l and 300-500 U/l, respectively, correspond to moderate disease activity, while values exceeding 750 U/l and 550 U/l, respectively, correspond to high RA activity. The anaerobic isoenzymatic distribution of LDH in rheumatoid SF results in a significant (p less than 0.001) decrease in LDH1 and LDH2 and an increase (p less than 0.001) in LDH4 and LDH5.