Mononucleosis Screen (Heterophile Antibody)
A quick blood test for heterophile antibodies, which most often appear during infectious mononucleosis (mono), usually caused by the Epstein-Barr virus.
AI-verified against cited sources. Awaiting expert reviewAlso called Monospot, IM screenLOINC 31418-7
What it is
Mono is a viral illness with fatigue, fever, sore throat and swollen glands. During mono, the immune system makes unusual antibodies called heterophile antibodies. This test looks for them. It is often called the Monospot test. The result is simply negative or positive. It is a screening test, and it is not perfect: it can miss mono early in the illness.
Why it matters
A positive result supports a diagnosis of mono when you also have the typical symptoms, which helps your clinician explain your illness and give advice about rest and activity. A negative result most of the time means you do not have mono, but it can be negative if the test was done too soon. Other tests can then check for Epstein-Barr virus (EBV) directly.
If it’s low
A negative result means no heterophile antibodies were found. Most of the time, this means you do not have mono. But it can be negative if the test was done within the first 1 to 2 weeks of illness, in young children, or in the small number of people with mono who never test positive. Other infections can cause a mono-like illness with a negative spot test, including cytomegalovirus (CMV), adenovirus, strep throat and HIV.
Common causes
- An illness other than mono, since many infections cause fever, sore throat and swollen glands
- Testing very early in the illness, before the antibodies build up
- Being a child, since heterophile antibodies are often not present in children with mono
- Mono that does not produce a positive spot test (this happens in a small number of people)
What can help
- If symptoms continue, ask whether to repeat the test or have EBV-specific antibody tests
- Ask whether other causes of a mono-like illness are worth checking
If it’s high
A positive result means heterophile antibodies were found. This is most often a sign of infectious mononucleosis. Your clinician will consider your symptoms and other blood tests too. In rare cases the test is positive without mono.
Common causes
- Infectious mononucleosis, usually from Epstein-Barr virus (the most common reason)
- Rarely, a false positive linked to hepatitis, leukemia or lymphoma, rubella, lupus or toxoplasmosis
What can help
- Ask your clinician about rest, fluids and when you can return to school, work and exercise
- Ask whether you should avoid contact sports for a while, because the spleen can swell during mono
What can affect your result
- Timing: antibodies take 1 to 2 weeks to appear, peak at 2 to 5 weeks and can last up to a year
- Age: the test is less reliable in children
- Other conditions: hepatitis, leukemia or lymphoma, rubella, lupus and toxoplasmosis can occasionally cause a false positive
- Test kits differ by brand and method (latex agglutination or immunoassay)
- Testing too soon after symptoms start (within the first 1 to 2 weeks) can give a false negative (MedlinePlus).
- A small number of people with mononucleosis never have a positive spot test (MedlinePlus).
- The test is less reliable in children, in whom heterophile antibodies are often not present even when they have mono (CDC).
- Rarely, the test is positive without mono, for example with hepatitis, leukemia or lymphoma, rubella, lupus or toxoplasmosis (MedlinePlus).
Heterophile antibodies are highest 2 to 5 weeks after mono begins and may be present for up to a year (MedlinePlus).
When to talk to a clinician
Contact a clinician if your symptoms last longer than 10 days, or if you develop belly pain, trouble breathing, a persistent high fever (above 101.5°F or 38.6°C), a severe headache, a severe sore throat or swollen tonsils, weakness in your arms or legs, or yellow skin or eyes. Call 911 or your local emergency number, or go to an emergency room, for sudden, severe belly pain, a stiff neck, severe weakness, or trouble swallowing or breathing. These can be signs of a complication of mono.
Questions you could ask
- How does the timing of my symptoms affect how to read this test?
- Do my symptoms and this result fit mono?
- When is it safe to return to sports and other activities?
- Should we repeat the test or check EBV-specific antibodies?
- Are other causes of my symptoms worth checking?
Questions people ask
My mono spot test is negative, but I feel terrible. Could it still be mono?
Yes. The test is often negative in the first 1 to 2 weeks and can stay negative in some people who have mono. Your clinician may repeat it later or order EBV-specific antibody tests. Other infections can also cause a mono-like illness.
How long does the test stay positive?
Heterophile antibodies are highest 2 to 5 weeks after mono begins and can be present for up to a year, according to MedlinePlus. A positive result alone cannot date the illness.
What other tests can show EBV infection?
Your clinician can order EBV-specific antibody tests, such as VCA IgM, VCA IgG and EBNA IgG, which look at your immune response to the virus itself. Together they help show whether an EBV infection is recent or old.
Show the science and sources
For clinicians and researchers
The heterophile (Paul-Bunnell/Monospot) test detects IgM heterophile antibodies that agglutinate red cells from other species. They are induced by EBV infection but are not EBV-specific. Results are qualitative; kits use latex agglutination, lateral-flow or immunoassay formats. MedlinePlus reports antibodies peaking 2 to 5 weeks into illness and persisting up to a year, with false negatives in the first 1 to 2 weeks and in a small group of true mononucleosis cases that never turn positive. Hurt and Tammaro (Am J Med 2007) emphasize that a negative spot test may occur early and that a growing list of pathogens cause heterophile-negative mononucleosis-like illness, including CMV, HHV-6, HIV, adenovirus, HSV, Streptococcus pyogenes and Toxoplasma gondii. When the spot test is negative and suspicion remains, EBV-specific serology can be used. For example, Mayo Clinic Laboratories' EBV antibody profile reports VCA IgM, VCA IgG and EBNA IgG, each with reference value 'Negative', and a technical interpretation. CDC reports that heterophile antibodies are often not present in children with infectious mononucleosis, and that the Monospot produces both false-positive and false-negative results and is not recommended for general use. EBV-specific antibody tests (VCA IgM, VCA IgG, EBNA) can be used when the spot test is negative and suspicion remains.
LOINC 31418-7 (primary), 6425-3, 11610-3. Specimen: serum.
Sources
- Mononucleosis spot test, MedlinePlus (NIH)
- Diagnostic evaluation of mononucleosis-like illnesses, The American Journal of Medicine (2007)
- Laboratory Testing for Epstein-Barr Virus (EBV), CDC
- Mononucleosis, MedlinePlus Medical Encyclopedia (NIH)
- Epstein-Barr Virus Antibody Profile, Serum (test EBVAB), Mayo Clinic Laboratories (Extended Catalog)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.