Relationship of the erythrocyte sedimentation rate to viscosity and plasma proteins in rheumatoid arthritis.

The best established laboratory test in the assessment of patients with rheumatoid arthritis is the erythrocyte sedimentation rate (ESR). It is a complex measurement, the major factor being variations in the plasma protein concentrations, but the number and shape of the erythrocytes also contributes substantially. At constant red cell concentration, the relative contributions of the plasma proteins to the ESR are fibrinogen 10, a2 globulins 5, y globulins 2, albumin 1 (Hardwicke and Squire, 1952). Increase in the concentration of fibrinogen and other macromolecules is associated with increases in both the ESR and the plasma viscosity. The increase in viscosity, which would be liable of itself to slow the sedimentation of the red cells, is more than balanced by the increased rouleaux formation and consequent more rapid rate of sedimentation. Artificial macromolecules, such as dextran and polyvinyl pyrrolidones, have the same effect (Hardwicke and Squire, 1952; Lawrence, 1961). In rheumatic diseases, Shearn, Epstein, Engleman, and Taylor (1963) have shown that the serum viscosity is principally affected by the concentration of the y globulins and of rheumatoid factor. A number of alternatives to the ESR have been suggested; these include plasma viscosity (Cowan and Harkness, 1947; Eastham and Morgan, 1965), serum and plasma viscosity (Hardwicke and Squire, 1952), and a modified plasma viscosity where allowance is made for the different plasma protein fractions (Lawrence, 1949, 1950). The present work was undertaken in an attempt to clarify the relationships between the ESR, the serum and plasma viscosity, and the plasma proteins with especial reference to the acute phase proteins.