Source and significance of raised serum and synovial fluid enzymes in rheumatoid arthritis

ABSTRACT

Fifty four patients with RA were included in the study. Blood samples were obtained from all cases and synovial fluid [SF] samples were obtained from 24 patients presenting with knee effusion. Besides routine tests of rheumatoid activity ESR, CRP, the following enzymes were analyzed in serum and SF samples alkaline phosphatase [ALP], LDH, 5'-nucleotidase [5'NT] and adenosine deaminase [ADA], quantitative determination of LDH isoenzymes and qualitative determination of ALP isoenzymes. Cytological examination of SF was also carried out. Results revealed elevated serum levels of ALP, LDH, 5'NT and ADA in 81%, 27.77%, 23.8% and 50% of cases, respectively. Significantly higher SF levels were found for LDH, 5'NT and ADA when compared with serum levels. The values were 240.5 +/- 149.6 U/l, 10.72 +/- 9.05 U/l, 52.79 +/- 27.78 U/l for SF and 182.75 +/- 97.46, 5.46 +/- 3.57 and 23.6 +/- 12.36 for serum enzymes, respectively. SF serum ratio demonstrated a value less than one for ALP, but greater than one for LDH, 5'NT and ADA, this signifies that ALP originates mainly from the liver and passes to joint fluid due to increased permeability of synovial membrane, while the other three enzymes most probably originate from the joint itself and diffuse to blood stream. Serum LDH isoenzyme pattern was predominantly of LD1 and LD2 25.1 +/- 5.44% and 33.42 +/- 8.72%, respectively, while SF LDH isoenzyme pattern was predominantly of LD4 and LD5 20.95 +/- 5.25 and 35.57 +/- 5.78, respectively. This shift of LDH isoenzyme pattern towards the slowly migrating form is probably due to increased demands of the highly cellular SF in RA for anaerobic glycolysis to supply its energy requirements. Serum LDH was significantly elevated in active RA than inactive cases, values being 311.85 +/- 97.86 and 208.12 +/- 104.53, respectively. A positive correlation was found between SF LDH and PMN cell count indicating the value of LDH as a marker of disease activity better than ESR