A spike protein test can mean two different things. A spike antibody test measures antibodies against the SARS-CoV-2 spike protein, which reflect past infection or vaccination (CDC). A spike antigen test measures the protein itself in plasma, and the long COVID studies that report it used research assays. Neither diagnoses long COVID, because no approved laboratory test for it exists (CDC).
Key takeaways
- Two different tests share the name: an antibody test and a research test for the spike protein itself.
- A positive spike antibody test can reflect past infection or vaccination; nucleocapsid antibody tests look for past infection in vaccinated people (CDC).
- A research assay found spike protein in the plasma of 60% of 37 people with post-acute sequelae, and in none of 26 people who recovered (Swank et al., 2023).
- A larger study found more viral antigen in people who had been infected than in uninfected people for up to 14 months, with the gap shrinking over time (Peluso et al., 2024).
- No approved laboratory test can determine whether symptoms are due to long COVID (CDC). Spike results describe groups in research and do not diagnose one person.
What does a spike protein test measure?
The spike protein sits on the surface of SARS-CoV-2, and the body makes antibodies against it after infection or vaccination. A test with "spike" in its name measures one of two things, and they answer different questions.
| Test | Measures | A positive result means | It cannot show |
|---|---|---|---|
| Spike antibody test | Antibodies against the spike protein | Past infection or vaccination (CDC) | A long COVID diagnosis |
| Nucleocapsid antibody test | Antibodies against the nucleocapsid protein | Past infection, including in vaccinated people (CDC) | A long COVID diagnosis |
| Research spike antigen assay | Spike protein itself in plasma | Viral antigen was present in the sample on the day of the draw (Swank et al.) | A diagnosis, or the reason for your symptoms |
The antibody tests are common and answer an immunity question. The antigen assays in long COVID research come from research laboratories and answer a question about viral material in the blood.
What did research find about spike protein in long COVID?
Two studies anchor the question. In 2023, Swank and colleagues used a sensitive research assay on plasma from people with post-acute sequelae of COVID-19. They found spike protein in 60% of 37 people with post-acute sequelae at some point 2 to 12 months after diagnosis, and in none of 26 people who recovered without them (Swank et al., 2023).
In 2024, Peluso and colleagues compared people who had been infected with people who had not. The infected group had more SARS-CoV-2 antigen in plasma for up to 14 months: 11 percentage points more at 3 to 6 months after illness, and 5.4 points more at 10 to 14 months (Peluso et al., 2024). The same study linked worse acute illness to more antigen afterwards.
These findings support a hypothesis that viral material can persist in some people after infection. Researchers study it alongside other explanations, including immune differences and reactivated latent viruses such as Epstein-Barr virus (Klein et al., 2023). No study has shown that persistent spike protein causes long COVID, and each describes groups. The long COVID guide sets the lines of evidence side by side.
Can a spike protein test diagnose long COVID?
No. The CDC states that there is no approved laboratory test that can determine whether symptoms or conditions are due to long COVID (CDC). Its clinical guidance adds that a positive SARS-CoV-2 viral or antibody test is not required for the diagnosis (CDC). Clinicians diagnose long COVID from the history, the timeline after infection and an examination.
A spike antibody result tells you about past infection or vaccination. A research antigen result tells you about one sample. Neither turns a group finding into an answer about you. If you have a spike antibody or antigen result, bring it to your doctor with your symptom timeline and the dates of any infections and vaccinations, which help read it. Our article on whether there is a test for long COVID covers what exists in 2026.
What can immune testing add?
A different kind of blood test looks at the body's response in place of the virus. Broad immune panels read cytokines such as IL-6 and TNF-α, interferons such as IFN-γ and the interferon-induced chemokine IP-10, each against a healthy reference. In a 2023 Nature study, immune profiling across many measures separated people with long COVID from people who had recovered, at the group level (Klein et al., 2023). A retest shows which way each marker moves.
Immune panels share the limit of every test on this page: they cannot diagnose long COVID or choose a treatment.
What is the next step?
For someone living with long COVID who wants objective data, research participation is a direct route. The Mune Mirror™* Baseline Study measures 50 people with long COVID and 300 healthy participants, starts on 15 October 2026, includes up to three at-home blood draws and returns each participant's own results. Sign-up is an application and does not guarantee a place. Read about the Baseline Study.
Where Mune Mirror™ fits
Mune Mirror™ measures more than 1,000 immune and inflammation proteins from an at-home sample, benchmarks each against a healthy reference and repeats the measurement over time. Unwellness testing is blood testing for people whose standard labs come back normal but who still feel unwell: the people medicine has no answers for yet. It measures highly selected immune and inflammatory proteins that routine panels do not, so persistent symptoms can be tracked and made visible against a healthy reference. Mune Mirror™ is investigational and for research and informational use. It does not diagnose, treat, cure or prevent any disease.
You can see what Mune Mirror™ measures. You bring the results to your own doctor.
Frequently asked questions
Can a blood test show spike protein in my body?
Research assays have measured SARS-CoV-2 spike protein in plasma, and studies found it in more people with post-acute sequelae than people who recovered. These are research tools. The result describes the sample on the day of the draw and does not diagnose long COVID.
Does a positive spike antibody test mean I have long COVID?
No. A positive spike antibody test can reflect past infection or vaccination, according to the CDC. It says nothing about long COVID, which has no approved laboratory test and which clinicians diagnose from the history and an examination.
What is the difference between spike and nucleocapsid antibody tests?
Spike antibodies can come from infection or from vaccines built on the spike protein. Nucleocapsid antibodies come from infection, so laboratories use them to look for past infection in vaccinated people. Neither test diagnoses long COVID.
Should I get a spike protein test?
Talk to your doctor about what you want the test to answer. A spike antibody test answers an immunity question about past infection or vaccination. Research antigen assays describe one sample and do not diagnose long COVID, so neither changes how clinicians diagnose it.
Does spike protein cause long COVID?
No one has shown that. Persistent viral antigen is one of several explanations researchers study, alongside immune differences and reactivated latent viruses. Studies describe associations in groups, and each leaves open questions about cause and direction.
Sources
- CDC. Interim Guidelines for COVID-19 Antibody Testing (archived).
- CDC. Long COVID Basics.
- CDC. Long COVID Clinical Guidance.
- Swank Z, et al. Persistent circulating SARS-CoV-2 spike is associated with post-acute COVID-19 sequelae. Clinical Infectious Diseases, 2023.
- Peluso MJ, et al. Plasma-based antigen persistence in the post-acute phase of COVID-19. The Lancet Infectious Diseases, 2024.
- Klein J, et al. Distinguishing features of long COVID identified through immune profiling. Nature, 2023.
Mune Mirror™ is currently in development, and the performance characteristics of this test have not yet been established. It is investigational. It does not diagnose, detect, screen for, treat, cure or prevent any disease. Results are for research and informational purposes, to discuss with your own doctor.