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What is Rheumatoid Arthritis (RA) Factor test?

Rheumatoid arthritis or RA is an autoimmune disease concerned primarily with joints. In this disease, the immune system reacts against body’s own tissue, producing antibodies that elicit inflammatory reactions in joints, leading to joint pain.

These antibodies are called rheumatoid factor (RF) antibodies. Although not specific to RA, it was one of the first factors found in the body of individuals affected by RA. In a healthy person, this factor is either present in deficient concentrations in blood or is not present at all. Therefore, an increase in this factor in the bloodstream could be an indication of RA or any other autoimmune disease. Corroboration with other diagnostic tests and symptoms helps confirm the diagnosis of RA.

  1. Why is RA factor test performed?
  2. How do you prepare for RA factor test?
  3. How is RA factor test performed?
  4. What do RA Factor test results mean?

RA factor  test is ordered in the presence of the following conditions:

Rheumatoid arthritis is not easy to diagnose as there is no single test available for its confirmation. Therefore, when an individual has symptoms pointing towards the possibility of RA and has high levels on tests such as CRP and ESR, the doctor orders an RA factor test.

CRP test checks for a protein which is also found elevated in the early stages of autoimmune disorders and is sometimes more useful than the RA factor test. A high ESR test suggests the presence of inflammation in body. Since RA is primarily an inflammatory disorder, ESR test results help corroborate the findings of RA factor tests. Therefore, a negative RA factor test does not always eliminate the risk of RA.

As the treatment of RA continues, it is expected for the levels of rheumatoid factor (RF) to fall back to normal. Therefore, to check the progress of the treatment, the doctor may order for RA factor, CRP and ESR tests.

No special preparations are needed for this test. However, it is important that you inform the doctor about any herbal supplements or medicines that you may be taking. A change in the course of medicines should not be done unless ordered by a doctor.

RA factor test is a simple blood test for which the sample can be done at any time. While collecting the sample, a technician ties a tourniquet around your arm and withdraws blood from a vein using a sterile needle. On the insertion of the needle, there may be a slight pricking pain, which disappears within a few seconds. Blood is then deposited in a sterile vial and sent for testing. The site of needle insertion is covered with cotton gauze and bandage to stop bleeding. Some people may experience slight bruising around the vein which will fade away soon.

Normal results:

Typically, results for the RA factor test are given as a titre ratio value. The normal results in terms of titre are:

  • Below 1:80 for individuals above 65 years of age
  • Below 1:40 for individuals between 16 to 65 years of age
  • Below 1:20 for individuals below 16 years of age

Results could also be given in nephelometric units, where the value indicates the amount of light scattering caused by RF in the sample. The normal results in terms of nephelometric units are below 30 units/mL.

The normal range can differ from one laboratory to another. It is crucial to refer to a doctor for the appropriate interpretation of results.

Also, it is important to remember that the RA factor test is not a confirmatory test for Rheumatoid arthritis. In some cases, persons showing normal results can also be diagnosed with RA with other diagnostic tests.

Abnormal results:

Higher than normal values of RF are common even in healthy aged individuals. Although it can be considered to be a sign of an inflammatory condition in body. Increased RF is seen not only in RA, but also in various other diseases like:

  • Autoimmune and connective tissue diseases such as:
    • Primary Sjogren’s syndrome
    • Systemic lupus erythematosus
    • Systemic sclerosis
    • Dermatomyositis/polymyositis
    • Systemic vasculitides
  • Infectious diseases such as:
    • HCV infection
    • Subacute bacterial endocarditis
    • Primary-tertiary syphilis
  • Cancers:
  • Others:

Although the RA factor test is a common indicator test for RA, it is always necessary to confirm the results with other diagnostic tests.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. Gerard J. Tortora, Bryan Derrickson. Principles of anatomy and physiology. 14th ed. Wiley Publication; 2014. Chapter 9, Joints; p.286-287.
  2. Marshal W.J, Lapsley M, Day A.P, Ayling R.M. Clinical biochemistry: Metabolic and clinical aspects. 3rd ed. Churchill Livingstone: Elsevier; 2014. Chapter 32, Biochemistry of articular disorders; p.637-645.
  3. Provan D, Oxford Handbook of Clinical and Laboratory Investigation. 4th ed. United Kingdom: Oxford University Press; 2018. Chapter 12, Rheumatology; p.750.
  4. University of Michigan [internet]; Rheumatoid Factor (RF)
  5. Ingegnoli F, Castelli R and Gualtierotti R. Rheumatoid Factors: Clinical Applications. Dis Markers. 2013 Nov 13; 35(6): 727–734.
  6. Provan D, Oxford Handbook of Clinical and Laboratory Investigation. 4th ed. United Kingdom: Oxford University Press; 2018. Chapter 4, Immunology and allergy; p.355.