Serum viscosity is a sensitive test for monitoring primary Sjögren syndrome.

Primary Sjögren's syndrome (pSS) is characterized by chronic inflammation, resulting in secondary changes in serum protein content. In an attempt to evaluate disease activity we have measured serum viscosity (SV) in 41 patients with pSS and compared SV with laboratory findings such as: total proteins, gamma-globulin concentrations, titre of rheumatoid factor (RF) and level of circulating immune complexes. SV was found to correlate with these laboratory parameters. The pSS patients with low serum viscosity had worse clinical abnormalities than those with the high SV. Thus SV affords a useful monitoring test for pSS patients.