Serum leucine aminopeptidase as an activity indicator in systemic lupus erythematosus: a study of 46 consecutive cases

Objective. To determine whether elevations in serum leucine aminopeptidase (LAP) levels reflected the underlying evolution of active disease in systemic lupus erythematosus (SLE). Methods. We studied serum LAP levels, other laboratory indicators, and SLE Disease Activity Index (SLEDAI) scores, in 46 consecutive patients with SLE admitted to Tokyo Metropolitan Komagome Hospital. LAP levels in 46 patients with rheumatoid arthritis were also measured. Results. Thirty-three SLE patients had elevated LAP levels. LAP levels correlated positively with levels of lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase and γ-glutamyl transpeptidase, and negatively with the total serum haemolytic complement and leucocyte, neutrophil and lymphocyte counts, but showed no correlation with alkaline phosphatase, γ-globulin, β 2 -microglobulin or C-reactive protein levels, or platelet count. The SLEDAI score correlated positively with LAP levels. The LAP level in patients with rheumatoid arthritis was near normal. Conclusion. The serum LAP level may be a potential activity indicator for SLE.