Did you test negative when sick or exposed to COVID? Here’s what it means

Update from 2023: Note that this blog, originally published in 2022, encourages PCR testing, but that isn’t always a feasible option anymore. Since the end of the COVID Emergency Declaration in May 2023, many community testing sites are no longer in service or may charge for testing.

The COVID testing, variant, and immunity (from vaccination and/or infection) landscape has changed a lot in 2022. Together, this means it can now be trickier to know if your test is giving you an accurate result.

Home tests are widely available, making testing easier than ever and are a convenient option for many people. But recently, we’ve been getting reports of some people in a household testing positive with a home test, while others in the home repeatedly test negative -- even if they were exposed to the positive person and have some symptoms. Below, we’ll answer some common questions to help you be more confident in your own test results.

What’s the difference between an antigen test (like an at-home test) and a PCR test?

A “PCR test” is a molecular test that finds genetic material from the COVID virus. These tests are very sensitive, meaning that they can detect even very small amounts of virus. Sometimes they can even detect traces of the virus after you are recovered and not contagious. PCRs take longer to get results because they need to be processed in a lab. If you pay out of pocket, they are expensive, but there are many free testing options in Dane County where you won’t be charged. The PCR is the most commonly used molecular test, but some other types are becoming more common, including rapid (or “point of care”) molecular tests. These tests can give results on-site in about 15 minutes, but are somewhat less sensitive than a PCR test.

Antigen tests, which include at-home rapid tests, look for proteins (“antigens”) of the COVID virus. These tests are less sensitive than PCR because they need a large amount of antigens to be present before they show a positive result. Studies have shown that if you test positive on an antigen test, you probably are contagious and can spread COVID to someone else. Antigen tests typically give results in just 15 minutes, can be done at home by yourself, and are much less expensive than PCR tests. Just be sure you read and follow the directions carefully. If you test positive on an antigen home test, let us know through our survey.

I tested negative even though I have symptoms and a likely exposure. Does that mean I don’t have COVID?

Testing negative does not necessarily mean you don’t have COVID. If you were exposed to COVID (e.g., someone you live with has it), and you have symptoms, but test negative on an antigen or PCR test, here are some possible explanations for what may be happening:

1. It’s too early, and your viral load may not be high enough to show up on a test. You will likely test positive eventually.

Symptoms are a sign that your immune system is working to fight off an infection. Symptoms can appear lot faster if you’re vaccinated, because your immune system recognizes the virus and is able to quickly react. Even if you are vaccinated, the virus may be able to make you sick and contagious, especially because the vaccines aren’t as good at stopping the Omicron variants. (But the vaccines are still good at keeping you out of the hospital!) The Omicron variants may also be harder to detect in the nose compared to earlier variants. And Omicron rapidly replicates in your body, which can cause people to begin having symptoms earlier.

If you test negative soon after feeling sick, you should test yourself again a few days after the day your symptoms started, when your viral load is likely to be at its highest.

2. Your immune system fought off the virus, and your viral load never got high enough to be found on a test.

As stated above, your symptoms are likely a sign that your immune system is fighting the COVID virus. If you have some symptoms and then feel healthy again, and have multiple negative tests throughout that time, it’s possible that your immune system was able to prevent the virus levels from getting high enough to be detected on an antigen or even a PCR test. Thanks, immune system!

The amount of virus present varies between people. Most people with COVID will have enough virus at some point to test positive on an antigen test. The amount of time it takes to test positive can vary widely. Some vaccinated people may never test positive on an antigen test, while others could be positive for many days in a row. Some people with mild infections may test negative on an antigen test, but positive on a PCR test. This would mean that they have COVID, but don’t have enough virus to turn an antigen test positive. This may be more likely to happen if a person has been recently vaccinated or boosted and their immune system is able to respond to the virus faster.

One study monitored health care workers and found evidence that some of people who were exposed were likely able to clear the COVID virus from their system before testing positive. We discussed immunity in a blog post at the end of last year!

3.  If you used an at-home test, there may have been user error that produced a false negative.

It’s important to carefully read and follow the directions on the at-home test. Tests can come from different manufacturers and have different instructions, so be sure to follow the directions specific to your test. Tests should be handled carefully and you should have clean, dry hands before using them. They should not be stored at extreme temperatures (e.g., don’t keep them in a car on a hot, sunny day), and you should be aware of the expiration date.

So if I tested negative, what should I do?

No matter what the situation, you should consider testing again one to two days after your negative test. If you get multiple negative test results, it is more likely that you are not infected with COVID. If you are feeling sick, even if it is not COVID, it’s still a good idea to stay home and not infect others.

If you were exposed to COVID, you should follow the guidance on our page: What to Do if You are Sick or Possibly Exposed.

• If you tested negative and are up to date on your COVID vaccinations: you should wear a well-fitted mask, preferably an N95, KN95, or equivalent, around others for 10 days after the last close contact you had with someone who tested positive. If possible, test yourself again a few days after your first negative test to make sure you are still negative.
• If you tested negative and are not up to date on your vaccines: you should quarantine for five days and wear a well-fitted mask, preferably an N95, KN95, or equivalent, around others for 10 days after the last close contact. If possible, test yourself again a few days after your first negative test to make sure you are still negative.
• If you have symptoms and tested negative: you should follow the above guidance and consider isolating, if you can, until your symptoms resolve. You should also consider getting a PCR test to confirm your negative test.

If I test negative with a home test but have symptoms, am I contagious?

You’re probably contagious with something! If you have symptoms, you should assume you are contagious, even if it ends up not being COVID. It would be best to isolate and test again after one or two days. If you test positive with an antigen test, you can be pretty certain that you are contagious with COVID. If you prefer a PCR test, we have many testing options listed on our website!

If I tested positive on a home test, does it really mean I have COVID?

Positive results are highly reliable, so yes, you very likely do have COVID, even if the line on the test is very faint. You should follow our guidance for what to do if you test positive, and you should also let us know about your positive test.

If you do test positive and are at high risk for developing severe COVID (e.g., have an underlying condition such as cancer or diabetes, or are age 65+), you should know that effective treatments, such as Paxlovid, are available. They require a prescription and need to be started within the first 5-7 days of symptom onset. Quick access to treatment can unfortunately be very challenging, even as supply has recently increased. For those with health insurance and/or access to a primary care provider, you should make an in-person or telehealth appointment to obtain a prescription as soon as possible. You can also check the federal government’s test to treat locator to see if there’s a location near you where you can get both a test and a prescription, fill a prescription, or schedule a telehealth appointment with a provider who can assess your eligibility and prescribe a treatment. You may also be able to use an online urgent care platform such as Plushcare or eMed, although these may come with out-of-pocket costs for an appointment.

For further reading, this topic was also recently covered by science writers in the New York Times and The Atlantic. Some of the above information was sourced from these articles. And thank you to our partners Dr. David O’Connor and Dr. Thomas Friedrich for help in writing and fact checking this blog post.