Rheumatoid factor (RF) is an antibody that can be found in the blood of people with rheumatoid arthritis (RA) and some other autoimmune diseases. A quantitative RF test measures the level of RF in the blood, which can help diagnose and monitor the progression of RA. The test involves taking a blood sample from the arm and sending it to a laboratory for analysis. The results of the test are reported in units per milliliter (U/mL) or international units per milliliter (IU/mL). Normal RF levels are generally less than 14 U/mL or less than 20 IU/mL, depending on the laboratory's reference range. Higher levels of RF in the blood may indicate the presence of an autoimmune disease, such as RA. However, high RF level does not necessarily mean a person has RA, as RF can be found in other conditions as well. In addition to the quantitative RF test, doctors may also order other blood tests, such as an anti-cyclic citrullinated peptide (anti-CCP) test, to help diagnose RA. Imaging tests, such as X-rays or MRI scans, may also be used to evaluate joint damage. If RA is diagnosed, the doctor may recommend a combination of medications, physical therapy, and lifestyle changes to manage symptoms and slow the progression of the disease.