What does a positive ANA or RF result mean?

If your lab sheet says “positive” next to ANA or RF, or a number above the normal range, your first thought was probably “so I have a disease.” It is too early for that conclusion. This article explains what these tests do and do not say.

What is ANA?

ANA, or antinuclear antibody, is a blood test that looks for antibodies that attach to the nucleus of the body’s own cells. MedlinePlus says doctors use it to help diagnose autoimmune diseases such as lupus, scleroderma and Sjögren’s.

The ACR writes that everyone has a small amount of this kind of antibody, and that a positive ANA is “not a sure sign of an autoimmune disease.”

How many healthy people test positive?

• ACR: up to 15 percent of completely healthy people have a positive ANA.
• MedlinePlus: many healthy adults, especially women over 65, may have a positive ANA. Some medicines, viral infections and some other illnesses can also make it positive.
• NIAMS: completely healthy people may also have a positive ANA, and a positive result alone does not confirm lupus.

How many people who test positive have a disease?

The ACR writes that only about 11 to 13 percent of people with a positive ANA have lupus or another autoimmune or connective tissue disease. On the other side, more than 95 percent of people with lupus have a positive ANA, so a negative result makes lupus unlikely. This means ANA is a “sensitive” test but not a “specific” one: it usually picks up patients, but sometimes picks up healthy people too. MedlinePlus also says a negative result makes an autoimmune disease unlikely but does not rule it out completely.

Titer and pattern

Sometimes the result is written as a ratio such as 1:160 (the titer), and a pattern is also reported. The ACR says that doctors look at the pattern and intensity under the microscope, and that some labs call only a titer higher than 1:160 positive. MedlinePlus gives no explanation of titer and pattern and advises that if they appear in your report, you ask your doctor what they mean. We also do not give a meaning based on a number or pattern.

What is RF?

Rheumatoid factor (RF) is a protein made by the immune system. MedlinePlus writes that doctors mostly order it together with other tests to help diagnose rheumatoid arthritis.

• A positive result alone is not a diagnosis. MedlinePlus says the doctor weighs it against symptoms, history and other tests.
• Healthy people sometimes have it. MedlinePlus: “Many people have small amounts of RF in their blood and are healthy.”
• It has other causes. MedlinePlus lists other autoimmune diseases (Sjögren’s, lupus, scleroderma), some chronic infections (such as hepatitis C and tuberculosis) and some cancers among the causes of a raised RF.
• A negative result does not rule it out. MedlinePlus says some people with rheumatoid arthritis have a low or negative RF.
• The NHS writes that in more than half of people with rheumatoid arthritis, RF is raised at the start of the disease, but about one in twenty people without the disease also test positive. The NHS concludes that no blood test can confirm or rule out rheumatoid arthritis.

Anti-CCP is another related test. The NHS says a positive result raises the likelihood of rheumatoid arthritis, but not everyone with the disease has it.

What should you do after a positive result?

1. Do not panic, and do not ignore the result. A positive result is neither a diagnosis in itself nor something unimportant to forget.
2. Read the result together with your symptoms. Tell the doctor about joint pain and swelling, rashes, dry eyes and mouth, mouth ulcers, sun sensitivity, Raynaud’s, and fever or tiredness. If you have no symptoms, say that too.
3. The doctor may ask for another test. MedlinePlus says that after a positive ANA the doctor will probably order more tests. For lupus, NIAMS names more specific tests (anti-Smith, anti-dsDNA, antiphospholipid), blood cell counts, and kidney and urine tests. The ACR says further tests, an examination and a review of history may be needed, and the rheumatologist decides on the next step.
4. Take your papers with you. Bring the original lab sheet (with the titer and pattern). See the “Your first visit and what to bring” guide.
5. Do not treat yourself. Do not start a medicine, diet or supplement because of a positive ANA or RF.

When should you be sure to follow up?

If you have autoimmune symptoms, for example a swollen, painful joint lasting several weeks or more, long morning stiffness, a facial rash after sun, mouth ulcers, dry eyes and mouth, or fingers that turn white or blue in the cold, make an appointment. For more urgent signs, see the guide “When should I call urgently?”

Summary

ANA and RF are clues, not verdicts. A positive result can lead the doctor to look further, but without symptoms and an examination it cannot tell you that you have a disease. What decides things is the whole picture: your symptoms, the examination and the combination of tests.