Quantification of the C3 breakdown product C3d by rocket immunoelectrophoresis

The levels of the C3 breakdown product C3d were measured in plasma, serum, and synovial fluid by the technique of rocket immunoelectrophoresis. Serum and plasma from 22 healthy donors, 4 patients with rheumatoid arthritis, 1 patient with systemic lupus erythematosus, and 1 patient with cryoglobulinemia were used. The synovial fluid was studied in 3 other patients with rheumatoid arthritis. Normal values for the 22 healthy donors in plasma were within a narrow range of 3.25--5.75% as compared to the standard pool that was prepared. Storage of plasma to -80 degrees C during 7--15 days did not modify the results of the test. Significant differences in C3d values were observed between serum and EDTA plasma samples. Patients with immunological diseases showed higher values of C3d in the samples (from 5 to 30% of activity as compared to the standard pool). Measurement of C3d by rocket immunoelectrophoresis showed to be an easy, satisfactory and reliable procedure able to be incorporated to routine immunological evaluations.