The relationship of plasma and serum viscosity to disease activity and smoking habit in rheumatoid arthritis.

Viscosity measurements of serum and plasma have been suggested as improvements on other indicators of activity in the rheumatic diseases. We compared the clinical assessment of disease activity in 71 patients with rheumatoid arthritis against various laboratory tests including viscosity measurements. The effects of smoking were also studied. While many of the tests showed correlations with each other, none was found to correlate with any of the clinical parameters. Smoking lowered the ESR, but did not affect the plasma viscosity in these patients. Thus viscosity measurements were no improvement in assessing activity in a cross section of patients, though its lack of dependence on smoking habit may be an advantage in sequential studies.