A positive ANA test doesn’t only point to lupus or other autoimmune diseases. Ordinary infections, from viruses to bacteria to parasites, can switch it on too.1PubMed. ANA testing in the presence of acute and chronic infections When the test is ordered for vague symptoms like fever, tiredness, aches or a rash, an infection becomes a more likely explanation, especially in children.2PubMed. ANA testing in the presence of acute and chronic infections After a short viral illness, these antibodies usually fade from the blood within weeks to months.3MedlinePlus. ANA (Antinuclear Antibody) Test A single positive result is a clue that needs context, not a diagnosis.
Why an Infection Can Turn the ANA Test Positive
ANA stands for antinuclear antibody. The test looks for antibodies in your blood that stick to the nucleus, the control center inside your own cells. Your report usually gives a titer, such as 1:40 or 1:160, which is how far the blood was diluted and still showed antibodies. Higher numbers mean more antibody. It may also list a pattern, like speckled or homogeneous, describing how the antibodies glow under the microscope.
Low titers such as 1:40 and 1:80 show up in a noticeable share of healthy people, so labs and doctors weigh higher titers more heavily. A titer of 1:160 or above draws more attention, but it still isn’t a diagnosis. Different labs may use slightly different cutoffs for calling a result positive.
Some germs carry pieces that look like parts of your own body, so antibodies made against the germ can also react with you.4PubMed. Molecular mimicry and autoimmunity A busy immune system fighting infection can also activate nearby antibody-making cells that aren’t aimed at the germ at all.5PubMed. Molecular mimicry and autoimmunity An infection that lingers keeps stimulating the immune system, which makes ongoing antibody production more likely.6PubMed. Molecular mimicry and autoimmunity
The nucleus gets targeted because your cells constantly shed bits of their nuclei as old cells die. During an infection more cells die than usual, so the immune system sees more nuclear material than it normally would. Normally the body clears this debris quietly and keeps antibodies against it in check. A strong, prolonged immune push can loosen that restraint for a while.
A positive ANA is sensitive but not specific: many things trigger it. Diagnosing lupus takes symptoms, exam findings and other tests together.
Viral Infections Linked to a Positive ANA
In acute cytomegalovirus (CMV) infection, about 8 in 10 people tested ANA positive.7PubMed. Antinuclear antibody positivity in acute Epstein-Barr virus and cytomegalovirus infections In acute Epstein-Barr virus infection, the cause of mono, it was closer to 3 in 10.8PubMed. Antinuclear antibody positivity in acute Epstein-Barr virus and cytomegalovirus infections People with a positive ANA also tend to have higher Epstein-Barr antibody levels, especially when the virus is new or reactivating.9PubMed. Elevated antinuclear antibodies and altered anti-Epstein-Barr virus immune responses Both illnesses can cause weeks of exhaustion, sore throat, swollen glands and fever, which overlaps with the vague symptoms that lead doctors to order an ANA in the first place. A recent mono-like illness is worth mentioning to the doctor who ordered the test, and mono and CMV antibody tests that show recent versus past infection can help sort out whether the timing fits.
About 1 in 5 people with long-term hepatitis C test ANA positive, compared with about 2 in 100 people without it.10PubMed Central. High prevalence of antinuclear antibodies in patients with chronic hepatitis C virus infection Women with hepatitis C are more likely than men to test positive.11PubMed. Antinuclear antibodies (ANA) in chronic hepatitis C virus infection: correlates of positivity and clinical relevance If liver blood tests are abnormal, doctors will usually check for hepatitis viruses before assuming the liver problem is autoimmune, and hepatitis B and C blood tests are routine in that situation. A positive ANA with hepatitis C doesn’t mean the person also has an autoimmune disease, though the two can occasionally exist together and need careful sorting. Hepatitis E also counts: about 1 in 4 people with it had a titer above 1:160, including some with no symptoms.12PubMed Central. Significance of Anti-Nuclear Antibodies and Cryoglobulins in Patients with Acute and Chronic HEV Infection
How often people with HIV test ANA positive varies widely, from about 3 in 100 in one group to roughly 1 in 4 in another.13PubMed. Autoimmune and rheumatic manifestations and antinuclear antibody study in HIV-infected Thai patients14PubMed. Anti-nuclear, anti-neutrophil cytoplasmic and anti-glomerular basement membrane antibodies in HIV-infected individuals When positive, these results were mostly low titer with a speckled pattern.15PubMed. Anti-nuclear, anti-neutrophil cytoplasmic and anti-glomerular basement membrane antibodies in HIV-infected individuals One group of people on HIV treatment showed positivity in about 7 in 10, though.16PubMed Central. Mapping of the Antinuclear Autoantibodies in Sudanese patients infected with Human Immunodeficiency Virus after HAART receiving: A cross-sectional study
Parvovirus B19, the cause of fifth disease in children, can mimic lupus in adults with fever, rash, joint pain, low blood counts and a positive ANA.17PubMed. Parvovirus infection mimicking systemic lupus erythematosus The reported adult cases that looked like lupus were all in women.18PubMed. Parvovirus infection mimicking systemic lupus erythematosus In one case, a previously healthy woman was first treated for lupus before parvovirus was found and the illness passed.19Journal of Rheumatic Diseases. Transient Systemic Lupus Erythematosus-like Syndrome Associated With Parvovirus B19 Infection: A Case Report A blood test for parvovirus B19 IgM antibodies can show a recent infection.
People who had COVID-19 were about 1.7 times as likely to later get a positive ANA as people who had not.20PubMed Central. New-onset autoimmune disease after COVID-19 After mRNA COVID-19 vaccination, about 1 in 20 people developed a new positive ANA, and it was gone by 3 months.21ACR Meeting Abstracts. Low Incidence and Transient Elevation of Autoantibodies Post mRNA COVID-19 Vaccination
Bacterial and Parasitic Infections That Raise ANA
Among hospital patients with a positive ANA and no autoimmune disease, infection explained about half of cases, with tuberculosis the most common.22PubMed. Antinuclear antibodies in infectious diseases About 1 in 11 people with active tuberculosis test ANA positive.23PubMed Central. Frequency of Positive Antinuclear Antibody in People With Active Tuberculosis and Its Changes With Antitubercular Therapy Syphilis, scrub typhus, E. coli and cat-scratch bacteria also appeared on that list.24PubMed. Antinuclear antibodies in infectious diseases
Tuberculosis is easy to miss. It can cause weeks of low fever, night sweats, weight loss and cough, which can be mistaken for an autoimmune illness when an ANA is positive. It can also affect places outside the lungs, such as lymph nodes or joints, so a lack of cough doesn’t rule it out. Doctors usually look for it with a skin or blood test and a chest X-ray when the history fits, such as past exposure or time in a high-risk region.
People with syphilis are more than twice as likely as others to have a positive ANA.25PubMed. Syphilis infection and autoimmune disease: A matched case-control study with clinical follow-up in 1,042 patients Syphilis can cause a rash and joint pain that, together with a positive ANA, get mistaken for an autoimmune disease.26Egyptian Rheumatology and Rehabilitation. Syphilis infection with ANA positivity: case series A blood test finds it, and antibiotics treat it. Since someone may not know they were exposed, the test is a simple step worth considering when the picture is unclear. About 1 in 7 people with Lyme disease test ANA positive at a titer of 1:200 or more,27New Medicine. Antinuclear antibodies in patients with Lyme disease so a tick bite raises Lyme as a possibility.
Infection of a heart valve, called endocarditis, shares many symptoms with lupus and can make the ANA positive.28Ibnosina Journal of Medicine and Biomedical Sciences. Infective Endocarditis is a Potential Differential Diagnosis of Systemic Lupus Erythematosus When the cat-scratch germ caused it, 4 in 10 people had a positive ANA.29PubMed Central. Bartonella Endocarditis-Associated Glomerulonephritis: A Mimicker of Autoimmunity and Vasculitis Fever with a new heart murmur and a positive ANA calls for blood cultures, not just autoimmune tests. People with heart valve problems or who inject drugs face higher risk.
Malaria can produce a distinctive pattern on the ANA test that can point a lab toward the right diagnosis.30PubMed Central. Chronic Malaria Revealed by a New Fluorescence Pattern on the Antinuclear Autoantibodies Test Leishmaniasis often causes a positive ANA, which commonly reverses after treatment.31Rheumatology Quarterly. Leishmaniasis and Autoimmunity: A Narrative Review Travel to areas where these occur changes what doctors test for.
How Doctors Tell Infection From Autoimmune Disease
Infections and lupus can share fever, joint pain, rash and low blood counts.32PubMed. Parvovirus infection mimicking systemic lupus erythematosus Some infections even produce anti-dsDNA, an antibody usually considered more specific for lupus.33Journal of Rheumatic Diseases. Transient Systemic Lupus Erythematosus-like Syndrome Associated With Parvovirus B19 Infection: A Case Report34PubMed Central. Bartonella Endocarditis-Associated Glomerulonephritis: A Mimicker of Autoimmunity and Vasculitis About 1 in 7 people with hepatitis C have antibodies on the ENA panel, the follow-up tests for specific antibodies.35PubMed Central. Anti-ENA antibody profiles in patients with hepatitis C virus infection
Your doctor will likely ask about recent fever, sore throat or swollen glands; travel, bites, animal contact and sexual history; whether symptoms came on suddenly or over months; and your medicines, since some drugs also raise ANA. Infections often start suddenly, with fever and feeling sick over days, while lupus more typically builds over weeks to months. Lupus sometimes begins abruptly too, so timing is one clue among several. Doctors also watch whether symptoms improve on their own, since many viral illnesses fade without treatment.
Tests beyond the ANA add information. Blood counts, kidney tests and a urine sample show whether organs are being affected in a way typical of lupus. Low complement levels, proteins used up in lupus, add more, though they aren’t decisive alone. Doctors pair these with infection-specific tests chosen from the history, such as viral antibody tests or blood cultures.
Antibodies from a short viral infection usually leave the blood within a short time,36MedlinePlus. ANA (Antinuclear Antibody) Test so repeating the test after the infection resolves often clarifies things. In leishmaniasis, the ANA often reverses after the parasite is treated.37Rheumatology Quarterly. Leishmaniasis and Autoimmunity: A Narrative Review Not every infection-linked positive is harmless, though: after COVID-19, people with a new positive ANA were far more likely to develop autoimmune disease.38PubMed Central. New-onset autoimmune disease after COVID-19 A positive that persists or comes with new symptoms deserves follow-up with a rheumatologist.
Ruling out infection first also protects you. Steroids given for presumed lupus can worsen an untreated infection, so it’s reasonable to ask whether infection testing was done before any immune-suppressing drugs.
What to Do After a Positive ANA
Before your follow-up visit, write down any illness in the past few months, even a bad cold or flu. Ask for your titer and pattern, since a low titer is weaker evidence. Children with vague symptoms are especially likely to have infection-related positives,39PubMed. ANA testing in the presence of acute and chronic infections so parents can ask whether a recent virus explains the result before further testing.
Build a timeline: when each symptom began, how long it lasted, and whether it came and went, since the order of events helps separate infection from autoimmune disease. Include recent vaccines, travel, tick or animal exposures and sick contacts at home. List every medicine and supplement, because some drugs can also cause a positive ANA. Vaccine-related positives were gone by 3 months,40ACR Meeting Abstracts. Low Incidence and Transient Elevation of Autoantibodies Post mRNA COVID-19 Vaccination so a repeat test a few months after a recent infection or vaccine is a reasonable plan to discuss.
Useful questions to bring: Could a recent or ongoing infection explain this? Which infection tests make sense for me? Do I need anti-dsDNA or an ENA panel? When should we repeat the ANA?
Seek care sooner for a persistent high fever, new chest pain or shortness of breath, swelling, blood in the urine, or a rapidly worsening rash.