There are two known types of rheumatoid arthritis: seropositive rheumatoid arthritis and seronegative rheumatoid arthritis.
What Is Seropositive Rheumatoid Arthritis?
Having seropositive rheumatoid arthritis means that your blood contains anti-cyclic citrullinated peptides (anti-CCPs), also known as anti-citrullinated protein antibodies (ACPAs), that have been solely created to target your body and trigger joint inflammation.1 These antibodies are produced in response to other body proteins that are currently undergoing citrullination, or a molecular change in structure.2
Testing positive for these antibodies, coupled with symptoms usually associated with RA, may lead to a possible RA diagnosis. As emphasized by the Illinois Bone & Joint Institute, anti-CCPs are said to be found in 60 to 80 percent of people battling RA, and research has suggested that these antibodies can appear in the body around five to 10 years before diagnosis.3
Seropositive RA may be diagnosed if rheumatoid factor (another antibody that may disrupt proper body function and attack healthy tissue) is present in the system too.4 This particular antibody can be detected by various tests and may also be visible in areas within other antibodies. However, take note that rheumatoid factor (RF) may manifest in people who have been diagnosed with other conditions. In some cases, patients who test positive for anti-CCPs also yield positive results for RF.5
What Is Seronegative Rheumatoid Arthritis?
Seronegative rheumatoid arthritis is the exact opposite of seropositive RA — patients do not have any of the aforementioned antibodies present in their system. In an article for the Arthritis Foundation, Dr. David Pietsky, professor of Medicine and Immunology at the Duke University School of Medicine, mentions: “You can have RA without being seropositive, but it is easier to meet the criteria if you are positive.”
A common sequence of amino acids, referred to as the shared epitope, may differentiate these two types of RA. These amino acids are “encoded” in the human leukocyte antigen (HLA) genetic site, which play a role in creating the proteins that manage immune responses. There is a theory that these amino acids attach themselves to protein parts called citrullinated peptides, and this affects production of anti-CCP antibodies.6
Other Ways to Differentiate Seropositive and Seronegative Rheumatoid Arthritis
Researchers are still determining other possible ways to differentiate these two types of RA, but some signs are already pointing to genetics. Certain genes may play a role in the development of other health problems linked to RA such as lung or eye problems, or rheumatoid or rheumatoid nodules.7
Some symptoms may also indicate the type of RA that a person is dealing with. WebMD notes that when compared to patients with seronegative RA, people who may have seropositive RA experience rheumatoid lung issues, develop nodules (swollen lumps beneath the skin) or vasculitis (blood vessel inflammation), and/or are affected with other diseases. Smokers also have a higher risk of being diagnosed with seropositive RA.8
Be Warned: Seronegative RA May Be Mistaken for Other Diseases
A patient already diagnosed with seronegative RA is unlikely to have a change of diagnosis and be classified as a seropositive RA patient. However, there is a chance that patients with seronegative RA may be experiencing another disease, such as:9
- Psoriatic arthritis: If the patient develops a skin rash, this type of arthritis may be diagnosed instead.
- Chronic gout: Patients who undergo joint fluid tests because of RA symptoms may actually have chronic gout.
- Osteoarthritis: There are instances wherein seronegative RA can be confused with this other type of arthritis.