Rheumatoid Factor Test, Nephelometry Test

A rheumatoid factor (RF) blood test is done to measure the amount of the RF antibody present in the blood. In normal cases, antibodies are produced by the immune system to fight and destroy the bacteria and viruses which are capable of causing disease. But the RF antibody can attach to normal body tissue, resulting in damage. Several autoimmune diseases can become a reason for a high level of rheumatoid factor. Occasionally an elevated level of RF is found in healthy people. The method used to measure the RF is called the Nephelometry test.

For the test to get conducted comfortably, it is advisable to wear something that has either no sleeves or those which can get easily rolled up. This is done because the elastic band is tied on the arm. Follow your normal routine as usual. No need to make changes to your meals or water intake. If any such precautions are required (it may differ from case to case) the doctor will let you know while recommending the test. It might happen that the doctor asks you to fast for few hours before or after the test is done. Always follow such particular instructions given to you in the lab.

A blood sample is mixed with antibodies to cause clumping. Later, laser light is passed through the sample to determine the intensity of cloudiness. Used as a blood test for the diagnosis of rheumatoid arthritis Rheumatoid factor can be positive for healthy people. RF can be positive for non-rheumatoid arthritis diseases and conditions. About 20% of people diagnosed with rheumatoid arthritis have negative RF.

An elastic band is wrapped around your upper arm to obstruct the flow of blood. This will help in enlarging the nerve below the band and making it easier to insert a needle into the vein without even feeling a thing. The needle site is cleaned using alcohol. The needle is inserted into the vein slowly. Sometimes more than one needle is also kept handy as it might be needed. A tube is attached to the needle to collect the extracted blood from the vein. When the required blood is collected the elastic band is removed from the arm. While removing the needle from the site, gauze or a cotton ball is placed to prevent any blood flow. Before the final bandage, a small amount of pressure is applied on the site.