The normal range of rheumatoid factor is 0~20IU/mL, and the test found that rheumatoid factor 300IU/mL is more serious. Usually rheumatoid factor is the most common test index for rheumatic immune diseases, which can be used for identification and diagnosis of systemic lupus erythematosus, rheumatoid arthritis, desiccation syndrome, systemic sclerosis, malignant tumors and other diseases. The normal range of Rheumatoid Factor is 0~20IU/mL. Before the test, it is better to fast for about 12 hours to avoid the effect of eating on the test result. Rheumatoid factor 300IU/mL is a more serious condition, significantly higher than the normal range. Generally it may be caused by rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis and other diseases, which may be complicated with vasoproliferative synovitis, which may lead to the destruction of cartilage tissues, and cause multi-system immune damage; secondly, when the human body enters into the period of advanced age, the rheumatoid factor titer will gradually increase, so it is necessary to exclude physiological factors. When the above symptoms appear, it is recommended to go to the hospital in time, and follow the doctor’s instructions to carry out standardized treatment as soon as possible.