Plasma and urinary levels of beta2 microglobulin in rheumatoid arthritis

Plasma and urinary levels of beta2 microglobulin have been investigated in 21 patients suffering from rheumatoid arthritis (RA). Despite a normal renal glomerular function in all patients 50% of them had supranormal plasma beta2 microglobulin levels and 30% had a higher than normal urinary output of beta2 microglobulin generally related to the high plasma level. Plasma beta2 microglobulin levels paralleled closely the lymphocytosis and the 'joint count' both indexes of the severity of the disease. beta2 Microglobulin was normally secreted by the lymphoid tissue and it is suggested that it reflects the increase of the total mass and/or membrane turnover of the lymphoid tissue in RA. beta2 Microglobulin may be considered as a good parameter of the degree of severity of the joint and extra-articular involvement as well as a useful tool for the evaluation of drug efficacy in rheumatoid arthritis.