Studies on renal disease in rheumatoid arthritis. Part 1. Renal function, mainly serum and urine β(2)-microglobulin concentrations.

Serum, urine and synovial fluid β(2)-microglobulin (BMG) was measured by radioimmunoassay (Phadebas β(2)-micro test) in 43 rheumatoid arthritis (RA) patients being treated with gold salts, in 9 patients with osteoarthritis (OA) and in 9 patients with renal disease. The relationships between BMG, RA activity index and renal function were investigated. The serum BMG level in the renal disease group was significantly inversely correlated with creatinine clearance. The 43 rheumatoid arthritis patients were divided into a proteinuria group and a non-proteinuria group. The serum BMG level was higher in the renal disease group than in the proteinuria group, and was higher in the proteinuria group than in the non-proteinuria group. The synovial gluid BMG level was measured in 16 patients with RA and in the 9 patients with OA. This measure was higher in the RA group than in the OA group. The 43 RA patients were divided into positive and negative groups by C-reactive protein, RA test results (erythrocyte sedimentation rate over 50 mm/h and under 49 mm/h), and γ-globulin levels (over 1.5 g/dl and under 1.49 g/dl). Serum BMG levels were compared in these two groups. They tended to be higher in the higher activity groups than in the lower activity groups. From these results, a serum BMG level below 3.15 μg/ml (which is higher than in healthy normals) was considered "normal" for RA. The non-proteinuria group was investigated in a 2×2 table divided at 3.15 μg/ml serum BMG level and 500 μg/l urinary BMG level. There were two patients with abnormal BMG levels in both serum and urine samples, two patients with abnormal levels in the serum sample, and two patients with abnormal BMG levels in only the urine sample. It was thought that some patients without proteinuria in crysotherapy started to show renal damage. The results suggest that during gold treatment RA patients require not only urinalysis, but measurements of serum and urinary BMG levels for possible renal damage