Rheumatoid Arthritis Test - Rheumatoid Factor (RF)

This blood test detects and measures rheumatoid factor (RF) in the blood to help diagnose the presence of an autoimmune disease, such as rheumatoid arthritis. 

Rheumatoid factor is an autoantibody, a protein which attacks a person’s own tissue. This is because the body’s immune system has misidentified its own tissue as a foreign threat, like a bacteria or virus. 

About 80% of people with rheumatoid arthritis will have a positive RF test result. Rheumatoid factor can also be detected in individuals with other autoimmune disorders, not only rheumatoid arthritis. 

What Is Rheumatoid Arthritis?

Rheumatoid arthritis is a chronic and destructive autoimmune disorder in which a person’s immune system mistakenly attacks their own joint tissue, causing painful swelling, stiffness, and decreased joint mobility. This causes inflammation in the synovium, a layer of soft tissue on the joints’ inner surface. 

Over time, rheumatoid arthritis can damage cartilage, the firm but flexible tissue that covers and protects the ends of bones at the joints. Joints can loosen and become unstable, and the inflammation can cause joint damage and deformity.

Rheumatoid arthritis most commonly affects the joints of the hands, wrists, elbows, feet, and ankles, and it is usually symmetrical (if one side is affected, so is the other). Rheumatoid arthritis can also affect other parts of the body, such as the skin, eyes, and lungs. It can progress slowly or rapidly, so its course varies between people. 

Left untreated, RA can develop complications like hardened or blocked heart arteries and lung scarring, increasing the risk of a shortened lifespan. To minimize RA’s health complications, it’s important to get an accurate diagnosis and proper treatment before significant, irreversible joint damage occurs.

About 1.5 million Americans have rheumatoid arthritis. It can develop in anyone at any age but usually develops between ages 30-60 in women and 60-80 in men. 

Symptoms of Rheumatoid Arthritis

A rheumatoid factor test may be ordered if you are experiencing signs of rheumatoid arthritis.

Signs of rheumatoid arthritis include:

• Joint pain
• Joint stiffness, especially in the morning
• Joint inflammation
• Fatigue
• Low fever

What Causes Higher Levels of Rheumatoid Factor?

A higher level of rheumatoid factor can be caused by certain autoimmune diseases, including:

• Rheumatoid arthritis
• Lupus
• Sjogren's syndrome

RF can also be found in individuals with infectious diseases, such as tuberculosis, mononucleosis, and syphilis, as well as those with liver diseases like cirrhosis and hepatitis. 

Occasionally, rheumatoid factor may be detected in healthy people. A small number of people may test positive with a high RF level but remain healthy and never experience symptoms. However, a study of elevated rheumatoid factor and long term risk of rheumatoid arthritis suggests that people in the general population without rheumatoid arthritis but with an elevated plasma level of rheumatoid factor have up to 26-fold greater long term risk of developing rheumatoid arthritis.

What Do High Rheumatoid Levels Mean?

Significant concentrations of RF along with symptoms can indicate the likelihood of having RA. Higher levels are generally associated with more aggressive symptoms and severe disease course. Test results may vary, depending on factors like age, gender, and health history. 

On its own, a positive test result for rheumatoid factor doesn’t necessarily mean a person has rheumatoid arthritis. A positive rheumatoid factor test along with imaging and other blood tests, like an anti-cyclic citrullinated peptide (anti-CCP) test, can help identify and diagnose rheumatoid arthritis. 

Sources

1. “What is Rheumatoid Arthritis?” Arthritis Foundation. https://www.arthritis.org/about-arthritis/types/rheumatoid-arthritis/what-is-rheumatoid-arthritis.php
2. “Rheumatoid Arthritis.” American College of Rheumatology. https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Diseases-Conditions/Rheumatoid-Arthritis
3. “RA Life Expectancy: Does Rheumatoid Arthritis Affect Life Span?” Rheumatoid Arthritis Support Network. https://www.rheumatoidarthritis.org/ra/prognosis/life-expectancy/
4. Nielsen, Sune F et al. “Elevated rheumatoid factor and long term risk of rheumatoid arthritis: a prospective cohort study.” BMJ via National Center of Biotechnology Information. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3435445/ 
5. “Rheumatoid Factor.” LabCorp. https://www.labcorp.com/help/patient-test-info/rheumatoid-factor-rf