Alkaline phosphatase activity in the serum of patients with rheumatoid arthritis.

Alkaline phosphatase (ALP) activity was determined in the serum of 145 patients with rheumatoid arthritis (RA) and of 56 patients with osteoarthritis (OA). The mean ALP concentration was 226.9 U/L in RA and 168.7 U/L in OA (p less than 0.001). The prevalence of hyperphosphatasemia was 28% in RA vs 7.1% in OA (p less than 0.01). ALP concentrations significantly correlated with the erythrocyte sedimentation rate (p less than 0.05). Eighteen out of 46 (39%) rheumatoid patients in whom ALP isoenzymes determination was performed showed a predominant liver fraction and 10 (22%) a predominant bone fraction. In women, both ALP and its bone isoenzyme correlated with the number of joints involved by RA. During the followup, major changes of the type of predominant ALP isoenzyme were observed.