Have you ever looked at your lupus test results and thought they looked like alphabet soup? The complex medical terms and abbreviations can leave you wondering what they mean for your lupus and overall health. It may be some time before your next doctor’s appointment, so it’s tempting to do some research on your own.
Many MyLupusTeam members have noticed ribonucleoprotein (RNP) values appearing on their test results, and they’re curious about what they are. “How many people have a positive test for RNP antibodies? And what type of lupus do you have?” asked one member. Many others replied they’re living with systemic lupus erythematosus (SLE), the most common type of lupus.
In this article, we’ll discuss what RNP antibodies are and what a positive RNP test result means. We’ll also explore other factors contributing to a positive test result and discuss questions to ask your doctor or rheumatologist for a better understanding.
If you’ve been living with lupus for some time, you likely know that rheumatologists use antibody tests to help make a diagnosis. Lupus is an autoimmune disease caused by your immune system attacking your healthy cells and organs. Specifically, it makes proteins known as autoantibodies that recognize antigens — certain parts of your own DNA and other proteins — as foreign invaders.
One of the most common antibody tests for lupus looks for antinuclear antibodies (ANAs) where the autoantibodies attack various components in the nucleus of the cell. According to Johns Hopkins Lupus Center, 98 percent of people with lupus test positive for ANAs. If you have a positive ANA test result, it may mean you have SLE or another rheumatic disease like these long-term autoimmune conditions:
Your cells contain genetic material and proteins that they need to function properly. Your genetic information is stored in your DNA. Your cells use RNA to copy information and instructions from DNA. These instructions are then used to make proteins. RNPs are made of two components — RNA and proteins that bind RNA.
People with lupus and other autoimmune diseases can have RNP antibodies that attach to RNPs in their cells. The antibodies act like flags that tell your immune system to attack your cells, causing inflammation and damage.
RNP antibodies are just one of many types of ANAs you may see on your lupus test results. They also go by many other names. Take a look at your latest antibody test results for any of the following:
Many people with a positive RNP test result also have anti-Smith (anti-Sm) antibodies. These antibodies also attach to a certain RNP and tell your immune system to attack your cells. Anti-Sm antibodies are typically only found in people with lupus, so they’re often used to help make a diagnosis.
Currently, there’s no single test that can diagnose lupus or other autoimmune diseases. Instead, your rheumatologist uses your symptoms and a combination of antibody, blood, and urine tests to make a diagnosis. A positive ANA test result is just one piece of the puzzle.
However, some specific ANA tests can be used to narrow down if you have lupus or a similar disease. If you have a positive anti-RNP antibody test result, it may mean that you could also have:
The accuracy of an RNP antibody test is measured by its sensitivity. This term refers to how well a test can correctly identify whether someone has a disease. For example, an RNP antibody test has 95 percent to 100 percent sensitivity in MCTD. This means that 95 percent to 100 percent of people who have MCTD will test positive for RNP antibodies.
On the other hand, the RNP antibody test has only 38 percent to 44 percent sensitivity with SLE. This means that only 38 percent to 44 percent of people with SLE will have RNP antibodies.
Mixed connective tissue disease is a rare inflammatory condition that is seen in people affected by multiple rheumatic diseases. MCTD also belongs to a category called overlap syndrome — you may have MCTD if you have symptoms of multiple diseases at the same time. Overlap syndrome is most common with lupus, rheumatoid arthritis, myositis (a disease that causes inflammation of the muscles), and scleroderma.
Some MyLupusTeam members have asked others if they’ve also been diagnosed with MCTD. “My doctor teeters between diagnosing me with lupus and MCTD. I have several markers for lupus but not enough for a definitive diagnosis. I’ve never heard of MCTD, does anyone have a similar story?”
Your rheumatologist may diagnose you with MCTD if you have symptoms of overlap syndrome and a positive RNP antibody test result. If you haven’t recently had an antibody test, but you’ve started to notice new symptoms, it may be time to talk to your doctor.
A common symptom of MCTD is Raynaud’s phenomenon, found in about 90 percent of people with MCTD. This condition causes the blood vessels in your fingers and toes to constrict (narrow) when you’re cold. You may notice your fingers turn blue or white, especially in the winter. After you get back inside or warm up, the rush of blood makes your fingers and toes swell, burn, or tingle.
Other signs of MCTD to look out for include:
ANA tests are a useful tool for diagnosing lupus, but did you know that they can also help predict your prognosis (outlook) with lupus? Studies show that people who have RNP antibodies may be more likely to have severe disease with lupus. This means you may be at a higher risk of developing complications from lupus, such as lupus nephritis — a type of renal (kidney) disease — or lung complications. Future studies will show the connection between a positive RNP test result and severe organ damage in lupus.
Having a positive RNP antibody test result with lupus also increases your chances of having MCTD symptoms. These symptoms are rarely seen in people with lupus who have a negative RNP antibody test result. Examples include lung disease, muscle and bone disease, and Raynaud’s phenomenon.
If your latest blood work showed a positive RNP test result, ask your doctor or rheumatologist about it. They can help you better understand what this information means for you and your overall health. Be sure to tell them if you’ve also been experiencing any symptoms of MCTD — this information can help your rheumatologist make a more informed diagnosis and update your treatment plan.
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Have you had a positive RNP test result? Have you talked to your doctor or rheumatologist about what it means for you? Share your experience in the comments below, or start a conversation by posting on your Activities page.