Relation between the affinity for congo red and the glycoprotein content of serum in rheumatoid arthritis and related diseases.

Disappearance of congo red from the serum has long been considered by many investigators to be the best and most constant indicator of amyloidosis. The congo red test, as shown by Bennhold (1923), measures the proportion of this dye which is retained in the plasma one hour after its intravenous injection. The validity of this test has been the subject of intense discussion. Disappearance of 40-100 per cent. of the dye from the serum within one hour is generally regarded as a positive test, but according to Stemmerman and Auerbach (1944) and Taran and Eckstein (1942) the test should not be considered positive unless 90-100 per cent. disappears. In an experiment of Dixon, Ramcharan, and Ropes (I1955), the congo red test tended towards positivity in 114 out of 227 patients with rheumatoid arthritis. In many cases of primary amyloidosis no affinity for congo red is found (Johansson and Pfeiffer, 1954), and Aegerter and Long (1949) demonstrated a positive congo red test in four out of five cases with systemic lupus erythematosus. These observations lead to the suggestion that the disappearance of congo red from the serum is due not only to the presence of amyloid in the tissues, but also to other factors. One such possible factor that can be studied is the binding of congo red to the serum. Since congo red does not penetrate semipermeable membranes, equilibrium analysis could not be used in the present study. The method herein devised is based on a partition analysis system. Cellulose powder, which has a great affinity for congo red, was loaded with congo red. Upon shaking this congo red loaded cellulose powder with a buffered serum solution, congo red is taken up by the serum. The dye-binding capacity of serum from patients with rheumatoid arthritis and