Testing for Coronavirus
updated June 25
If someone tells you they had a test for coronavirus and it came back negative, what does this actually mean? You really need to know the answer to this question !
There are 2 kinds of tests* for coronavirus:
- One is to detect if someone has the virus
- The other is to detect if someone has developed antibodies to the virus.
- These are not the same thing.
Testing for the virus means testing for the presence of viral RNA (genetic material unique to the virus). This test has been available for a while. Testing for the antibody (Ab), also called serology testing, means that a person has had the virus at some point (they might still have it or might be over it) and now their immune system has developed antibodies to the virus. This Ab test is also available, but it's a "buyer-beware" situation for now.
(*A third type of test has been released, called a viral antigen test. On May 9, Quidel Corp. received FDA Emergency Approval (EUA) for the nation's first Corona Antigen Test. But, this test has a high rate of false negatives - see below). Antigen refers to a viral protein that is specific and unique to COVID-19. Ideally, an antigen test will be a 10 minute one-time use disposable test - like a pregnancy test. One day we will be able to do millions of viral antigen tests every day.)
Many patients who develop the COVID illness are contagious before they get ill. This is called the “presymptomatic” phase. We know that a large percentage of people (from 50% to 80% of people in some studies) infected with the virus might develop minor symptoms, not even realizing that they have coronavirus, or maybe never get symptoms at all (asymptomatic). We do not know how long someone can be contagious before developing symptoms. Maybe a few days, maybe longer.
Currently, viral testing is mainly done on people with symptoms. As testing availability grows, we should be able to test anyone who wants one. It could be weeks or longer before there are enough tests to do this. But, the viral RNA test is labor intensive and involves multiple steps, which is why it will be extremely difficult to ramp up to millions of tests per day which is what the experts feel is needed to safely "open up" the country.
Without a test, how would someone who is asymptomatic and yet still contagious be identified?
Answer: they aren't.
Testing for the Virus
Testing a patient who is sick involves testing for the RNA of the virus. This is from a swab usually collected from the nose or mouth, or perhaps saliva. This can be positive during the “presymptomatic phase” and can also be positive after a patient with the virus starts to feel better.
If someone has been exposed recently and feels fine, a negative viral RNA test is not helpful. Maybe it was done too soon. Maybe in 1-2 days the test would become positive if repeated. But a negative test in someone who previously tested positive is a good indicator that they are no longer contagious.
A positive RNA test could mean that someone is contagious, but it could also be detecting damaged RNA from dead virus in a patient who perhaps is no longer actually contagious. People recovering from COVID can test positive for weeks after they feel better. We do not know if they are contagious or if the test is merely identifying viral remnants still in the tissues.
To be safe, people who feel better from a recent corona virus infection but still test positive should consider themselves to still be contagious. Eventually the RNA test will be negative, and this would be considered a safe sign that someone is no longer contagious (The CDC requires 2 negative tests done at least 24 hours apart for healthcare workers to be able to return to work). If there are no test results, the CDC requires 10 days (this used to be 7) of no symptoms, after recovery from COVID, in order to be safe to return to work.
Antibodies are proteins made by the human immune system and their job is to destroy invading bacteria and viruses (germs). Vaccines work by introducing parts of a germ so that the antibodies produced by the body will prevent infection by that germ in the future.
Sometimes antibodies last forever. Childhood vaccination for measles usually results in life-long protection. Sometimes booster shots are needed like for tetanus or whooping cough, and these are required every 10 years. We do not know if corona antibodies confer lifelong protection from COVID-19 but with other coronaviruses they do, so experts are hopeful. More research is needed on this question.
Antibodies (Ab) produced by the body are specific to each infection, and it takes the body about a week to develop measurable antibodies the first time a new germ is encountered. During this time, the virus can multiply at will.
At some point in the fight with the illness, the antibodies will show up. Once they form, they are normally in your body for the rest of your life, sometimes at high levels, and sometimes at very low levels. But even a low level of Ab can save your life because if that same virus ever tries to infect you again, the body can make billions more Ab to the virus very fast and attack it before it spreads. This is the miracle of the human immune system.
Antibody testing (often called serology testing) is mainly useful for people who feel fine. Antibody testing might be used to determine who is safe to return to work. Recently antibody testing for coronavirus (COVID-19) of thousands of randomly selected people in L.A. showed that almost 5% of them were positive. In NYC, 20% were positive! This shows how useful antibody testing can be. Millions of people are likely already immune to COVID and don’t even know it. If we could test everyone, then millions of people could learn that they are already immune to the virus.
Positive Vs. Negative Ab tests
A positive Ab test can be a true positive or a false positive. A True Positive test result means the Ab test is positive and you actually do have the Ab. This is how the test is supposed to work. BUT, this does not mean that you aren't contagious.
During the middle phase of the COVID illness, you can have the virus in your system and have antibodies at the same time.
A False Positive test means the test shows positive, but you do not have the corona Ab in your system which means the test was wrong. Maybe it found similar antibodies in your blood to other corona viruses, which is a real possibility.
A false positive result is a very dangerous result. This is the reason why we have to be careful when we embrace the new Ab tests coming at us. Many of these Ab tests are bypassing FDA evaluation. The few tests that have been studied have been shown to be up to 20% inaccurate. This is not good.
How do you know if a positive Ab test is a true positive or a false positive?
Right now, you don’t. Imagine you had a recent illness (maybe corona, maybe not?) and then get a positive Ab test for corona. Can you trust it? Does this mean you will no longer have to socially distance and can stop wearing your mask? NO, it does not mean that.
Think of the Ab test like a pregnancy test. Do not let one result affect you. Repeat the test. Better yet, repeat it using a different version of the test. Meanwhile, continue to follow safe virus-avoidance practices.
A negative Ab test can be a True Negative or a False Negative. A True Negative result means that you do not have detectable Ab to COVID. The timing of the test can matter. You can have COVID in the early stage and still have a negative antibody test, and a few days later your Ab test will likely turn positive.
A False Negative result means you are immune (probably-see above) to COVID but the test did not confirm it. Maybe the test kit was defective or just wrong. Maybe your Ab level was low and the test could not confirm it. This is disappointing but not dangerous. How do you know if a negative Ab test is a true negative or a false negative? You don’t.
If you think you had COVID but your Ab test is negative, consider repeating it. But do not assume you are immune to COVID if your Ab test is negative.
Beware the False Positive Ab test
Keep in mind the most important consideration. A positive Ab test might be a False Positive and people who stop following safe virus-avoidance practices based on a positive test could be placing themselves and their families in danger. Double or even triple check a positive result so you can be certain that you are no longer vulnerable to COVID.
Testing the Population
If the Ab test were widely available and accurate, this would be of tremendous benefit to society. Imagine testing thousands of people for Ab to the virus. Select a valid cross-section of society. This is what survey and poll takers do all the time when they are checking people’s opinions. We can also do this to check people’s immunity status. Then we will finally know how many people have actually had COVID. It is a lot more than most people think.
We know that many more people than reported on the news have had the virus but were never tested for it. How many is not certain. We need more Ab testing to know the true number. Maybe 10 million here in the US have had it, maybe 20 million, nobody can say for sure. The only way to know for sure is to perform Ab tests on everyone in the US, which is unrealistic. The next best thing is to test representative populations which is being done.
Proof of Immunity
There has been discussion of governments issuing people proof of immunity documents. Maybe it would be okay to let those who are immune return to normal activities. This is a complicated issue. It could result in two classes of citizens, the immune ones and the non-immune ones. History tells us that divisions like this can lead to significant unanticipated consequences. The medical community is very hesitant about claiming a positive Ab means that someone is immune.
T-cell immunity: a new discovery is that low blood Ab levels might not mean a person isn't immune. Antibodies are made by B-cells, but T-cells are a powerful weapon the body uses to kill germs and T-call immunity for a specific agent cannot be tested for. "Two studies reveal infected people harbor T cells that target the virus—and may help them recover. Both studies also found some people never infected with COVID have these cellular defenses, most likely because they were previously infected with other coronaviruses."
Stay cautious for now
Antibody tests are new and not widely available. This will change soon. Over one hundred companies are providing these tests and almost none are FDA-approved. The quality and cost vary widely and the results may not be accurate. Some physicians decline to perform these Ab tests due to their unreliability at this time.
We must be calm and vigilant and continue to follow the practices that are saving lives. Social distancing, stay-at-home if possible, wear masks in public, practice excellent personal hygiene at all times, use hand sanitizers, and watch for early signs or symptoms of illness.
Soon there will be FDA-approved highly accurate and quick-results antibody tests and viral antigen tests. Knowing quickly if you are immune, or being able to find out in minutes if you have the virus, will get us much closer to having a (new) normal life.
The FDA requires all commercial test manufacturers to apply for an emergency use authorization (EUA) to offer their tests on the market. The FDA has also provided recommended performance criteria for these tests. Tests developed as laboratory-developed tests (LDTs) will still be allowed to be offered without going through the EUA process. The FDA is concerned because the market is being FLOODED with Ab tests, many from previously unheard of labs. Medi-spas, weight loss clinics, and chiropractors are now offering Ab tests for $100 or more. These tests can be quite inaccurate and we do not advise anyone having an Ab test done until they can get an FDA-approved version.
Take Home Messages
- Current Ab tests are not FDA approved and can be unreliable.
- A positive Ab test can be a false positive. Do not assume your are immune.
- A positive Ab test early in the disease does not mean that you are no longer contagious.
- A positive Ab test and a negative viral swab test, if you had COVID and now feel normal, suggests that you are no longer contagious.
- If someone says they tested negative for the virus, there is no way to know what this means unless you know what type of test they did.
- NONE of the tests are 100% accurate.
How to get a COVID test
Los Angeles County COVID Testing
The City of Los Angeles, in partnership with the County of Los Angeles and CORE (Community Organized Relief Effort), is providing free COVID-19 testing to ALL Los Angeles County residents, whether or not you are experiencing COVID-19 symptoms. Priority for the same or next day testing is still given to people with symptoms, such as fever, cough, shortness of breath, chills, muscle pain, headaches, sore throat, or a new loss of sense of smell. Testing is by appointment only.
To find out if you're eligible for a test and to schedule an appointment at a drive-up mobile testing site in Los Angeles County, please click here.
Rose Bowl test location - IS CLOSED
Huntington Hospital COVID Testing
High-risk, very ill individuals requiring hospital care receive testing in the ER and in the hospital. They also provide limited testing at their outpatient facility, with a doctor’s order and appointment.
Outpatient testing: Huntington Hospital has an outpatient facility that is providing testing, by appointment, for patients with an order from their primary care physician. Call your physician for details. "Tests at the outpatient location are processed by independent commercial labs and we cannot influence the speed of test result returns. Test results will be returned to the ordering physician; if you are awaiting test results please contact your physician directly."
Exer Urgent Care
Exer is offering COVID-19 testing with results in approximately 24 to 48 hours at all Exer Urgent Care locations. Testing is only available for patients who have been screened and received a testing referral from one of their providers through VirtualCare by Exer or at one of their clinics. Exer provides COVID-19 testing for at-risk patients, based on guidance from the CDC and LA County Public Health Officials. In response to Los Angeles Mayor Eric Garcetti’s guidelines on increasing the categories of individuals who can get tested for COVID-19, Exer has expanded its testing criteria for the novel coronavirus to anyone exhibiting symptoms.
CVS - including CVS Pasadena
CVS is expanding its COVID-19 testing program by opening 91 more sites across California at select drive-thru locations. A testing kit will be provided to people in their cars at the drive-thru window or at a location in the parking lot and instructions will be given.