Serum beta 2-microglobulin, sialic acid, and C-reactive protein in systemic lupus erythematosus.

Serum beta 2-microglobulin (beta 2m), sialic acid and C-reactive protein (CRP) were studied in 58 patients with systemic lupus erythematosus (SLE) on 186 occasions. Serum beta 2m was significantly higher in SLE patients than in control subjects. Increased serum beta 2m levels were seen in 68% of the patients with only extrarenal manifestations of SLE, in 75% of the patients with renal manifestations but normal glomerular filtration rate, and in 100% of the patients with renal failure. Serum beta 2m levels in 12 SLE patients with associated Sjögren's syndrome were similar to those in patients without that syndrome. Serum sialic acid was also significantly increased in the SLE patients. Sixty-one (33%) of the 186 sera were positive for CRP (greater than or equal to 5 mg/l). The CRP elevation was not accompanied by recognized intercurrent infection or other superimposed cause of tissue injury and inflammation in 37 instances (61%). Under such conditions CRP was only moderately increased.