COVID-19 Testing

Section Editor: Rodney E. Rohde PhD
June 2, 2026

COVID-19 is an illness caused by a virus called SARS-CoV-2. A virus is a tiny infectious particle, too small to see without a microscope, that can cause illness. Your test report may use the name SARS-CoV-2 to refer to the virus that causes COVID-19. There are three main types of tests for COVID-19, and each one looks for something different, so knowing which test you had is the key to understanding your result.

This article explains the three types of COVID-19 tests, what the wording on your report means, and why two results can sometimes seem to disagree, so you can better understand a report you have received.

What COVID-19 tests look for

The three tests fall into two groups based on what they search for.

A PCR test — looks for the virus’s genetic material, the molecular instructions (made of a molecule called RNA) that are unique to the virus.
A rapid antigen test — looks for proteins from the surface of the virus.
An antibody test — looks for antibodies, which are proteins your immune system makes after meeting the virus or after vaccination.

The first two tests look for the virus itself, so they are used to find a current infection. The antibody test looks for your body’s response to the virus, so it is used to show a past infection or a response to a vaccine, not a current infection. (These three types of tests are explained in more general detail in a separate article on PCR, antigen, and antibody tests.)

PCR tests for COVID-19

PCR stands for polymerase chain reaction. It detects the virus’s genetic material and is usually performed on a swab from the nose or throat, and sometimes on saliva. PCR is the most sensitive COVID-19 test, meaning it rarely misses a true infection, and it is often used to confirm a rapid test result.

In the report, a PCR result is usually written as detected or not detected, and sometimes as positive or negative. A “detected” result means the virus’s genetic material was found, which usually indicates a current infection.

One point often causes worry and is worth understanding. A PCR test can stay positive for days to weeks after you have recovered and are no longer contagious. This is because PCR detects leftover genetic material rather than the whole, infectious virus. A positive PCR result soon after a recent infection does not necessarily mean you are still able to spread it. Some reports also include a value called the cycle threshold (Ct), which roughly indicates how much genetic material was present; a lower number means more. A Ct value is not a reliable measure of how sick or how contagious a person is, and it should be interpreted by your healthcare team rather than read on its own.

Rapid antigen tests for COVID-19

A rapid antigen test, sometimes abbreviated as RAT, detects proteins from the virus. These are the rapid tests often done at home or in a clinic, with results available in minutes. The result is usually reported simply as positive or negative.

How much you can rely on the result depends on which way it comes out:

A positive result is usually trustworthy — especially if you have symptoms. It generally means a current infection.
A negative result is less certain — A rapid antigen test needs a larger amount of virus to turn positive than PCR does, so that it can miss an infection, particularly in the first day or two, or when the amount of virus is low. Testing again after a day or two improves reliability, and a negative rapid test may be confirmed with a PCR test.

Antibody (serology) tests for COVID-19

An antibody test, also called serology, looks for antibodies in a sample of your blood. It shows whether your immune system has responded to the virus or to a vaccine. It does not diagnose a current infection, because antibodies take one to several weeks to develop after an infection begins. The period early in an infection, before antibodies have appeared, is called the window period. Results are usually reported as reactive or non-reactive, or as positive or negative.

An important detail is which antibody the test measured, because this changes what a positive result means. Antibodies against one part of the virus, called the nucleocapsid, usually indicate a past infection, because most COVID-19 vaccines do not elicit them. Antibodies against another part, called the spike, can come from either a past infection or a vaccine. For this reason, a positive antibody test does not always tell you on its own whether you had the infection or were vaccinated, unless the specific antibody is known.

How to read your COVID-19 result

The meaning of your result depends on the test type. The points below cover the wording you are most likely to see.

Detected or positive on a PCR or antigen test — The virus was found, which usually means a current infection.
Not detected or negative — The virus was not found. With a rapid antigen test, a negative result is less certain, especially early, and may need to be repeated or confirmed with a PCR test.
A positive PCR weeks after a known infection — May reflect leftover genetic material rather than a new or still-contagious infection.
Reactive or positive antibody test — Shows past exposure to the virus or a response to vaccination, not a current infection. The exact meaning depends on which antibody was measured.
Non-reactive or negative antibody test — No antibodies were found. This can mean no past infection, no vaccine response yet, or that it is still too early for antibodies to have developed.

Why your results might seem to disagree

It is common to have two COVID-19 results that appear to conflict. In most cases, this is not an error because the tests look for different things at different points in an infection.

Rapid antigen negative but PCR positive — PCR can detect much smaller amounts of virus, so it may be positive when a rapid test is still negative, especially early in an infection.
PCR still positive after you feel better — PCR can detect leftover genetic material for weeks, which does not necessarily mean you are still contagious.
Antibody positive but PCR and antigen negative — This points to a past infection or vaccination. The virus itself is no longer detectable, but the antibodies remain.

What happens after a COVID-19 test

A COVID-19 test describes what was found and informs the decisions you and your healthcare team make together, rather than dictating them on its own. Your result is interpreted alongside your symptoms, your possible exposure, the timing of the test, and your overall health.

Recommendations about isolation and returning to your usual activities come from public health authorities and change over time, so it is best to follow the current guidance for your area. For some people, especially those at higher risk of severe illness, a positive result may lead a doctor to consider treatment. Whether treatment is appropriate, and which kind, is a decision to make with your healthcare provider, and it is often most useful early in the illness. If a rapid test is negative but your symptoms continue, the test may be repeated or followed by a PCR test.

Questions to ask your doctor

Which type of COVID-19 test did I have?
Does my result mean I have a current infection, a past infection, or a response to vaccination?
If my rapid test was negative but I have symptoms, should I repeat it or get a PCR test?
I tested positive on PCR weeks after being sick. Does that mean I am still contagious?
What does my antibody result tell me, and which antibody was measured?
Could it be too early in the infection for this test to detect it?
Am I at higher risk of severe illness, and should treatment be considered?
What does current public health guidance recommend for someone with my result?
Could this be a false positive or a false negative result?
Who should I contact if my symptoms get worse?