We estimated the sample size based on the data of the positive rates of RF_IgA, RF_IgG, and RF_IgM in the peripheral blood, and the results showed that the sample sizes required for RA patients and control groups were 18 cases, 11 cases; 17 cases, 10 cases, and 13 cases, 8 cases, respectively. This evidence concerns the gene CD40LG and rheumatoid arthritis.