Coronavirus (COVID-19) Testing
- Molecular or antigen test: When you have symptoms of SARS-CoV-2 infection and/or have been exposed to someone with the virus
- Antibody test: When you previously had or suspected you had COVID-19 and your healthcare provider wants to determine if you have antibodies to the virus
- Molecular or antigen test: To diagnose current infections, a nasopharyngeal (NP) swab, a nasal swab and/or a throat swab is collected; sometimes a saliva sample may be collected.
- Antibody test: A blood sample is drawn from a vein or is collected from a fingerstick.
Coronavirus disease 2019 (COVID-19) is the name of the illness caused by the new strain of coronavirus called SARS-CoV-2. Diagnostic tests detect either the genetic material (RNA) of the virus or viral proteins (antigens) in a sample from the respiratory tract. COVID-19 serologic blood tests detect antibodies produced in response to the SARS-CoV-2infection.
SARS-CoV-2 is a new (novel) virus that first appeared in December 2019 and spread throughout the globe at an alarming rate, prompting the World Health Organization to declare the outbreak a pandemic and the U.S. Department of Health and Human Services to declare a public health emergency. As the pandemic continues, scientists continue to study the virus and learn more about COVID-19.
There are seven coronaviruses that are known to infect humans, and most cause mild to moderate respiratory symptoms. However, the disease resulting from SARS-CoV-2 infection is like MERS (Middle East respiratory syndrome) and SARS (severe acute respiratory syndrome) because it can cause more severe illness and, in some cases, lead to pneumonia and death.
Because SARS-CoV-2 is a novel virus, everyone is potentially susceptible to infection and, at this time, it is not known who may develop serious complications. Unlike seasonal influenza, which can also cause serious illness and death, there is no vaccine or specific treatment for SARS-CoV-2 infection yet.
About 1 to 2 weeks after infection, the body begins to produce antibodies to the virus, with the level gradually increasing over time. However, it is not yet known how long people continue to produce antibodies and whether the antibodies protect against re-infection, providing immunity. (For more general information on antibodies, including IgG, IgM and IgA, read the article on Immunoglobulins)
Some infected people may be asymptomatic or have no noticeable symptoms and yet be contagious, potentially spreading the virus to others (silent carriers). Many of those infected have no symptoms or mild to moderate illness and will recover within one to two weeks. If symptoms of COVID-19 develop, they typically appear within 2 to 14 days of exposure to the virus. Research suggests that the average time from first exposure to getting sick (incubation period) is about 5 days, and about 97% of people who develop symptoms will do so within 11 days.
The key symptoms of COVID-19 are coughing, shortness of breath or difficulty breathing. Additional symptoms may include fever, chills, repeated shaking with chills, muscle aches, headache, sore throat and loss of smell or taste. Symptoms may come and go, and there may be periods of time where someone with COVID-19 feels better. Children and babies generally have a milder illness but will often have the same symptoms as an adult.
The risk of serious disease increases with age and with having underlying health conditions, such as heart disease, lung disease, high blood pressure, diabetes or a weakened immune system. Some people with COVID-19 may develop pneumonia, a lung infection, and in severe cases, a ventilator may be needed to ensure enough oxygen. Although COVID-19 is primarily a respiratory infection, researchers are learning that the illness may affect other organs besides the lungs, such as the heart, brain, and kidneys. In the most severe cases, COVID-19 may lead to organ failure or death.
Tests for COVID-19
The initial signs and symptoms of COVID-19 are frequently difficult to distinguish from those of a common cold or of other respiratory illnesses, so testing is necessary to help diagnose a current or past infection.
- Reverse Transcription Polymerase Chain Reaction (RT-PCR): Most tests to check for current SARS-CoV-2 infection rely on RT-PCR testing to detect the virus's RNA in a respiratory tract sample from a patient. PCR is a laboratory method used for making a very large number of copies of short sections of DNA from a very small sample of DNA so that it can be detected. This process is called "amplifying" the DNA. (See the article on PCR for more details.) The reverse transcription step allows the viral RNA to be converted into DNA so that the PCR technique can be used.
- Rapid Antigen Tests: These tests detect the viral proteins of SARS-CoV-2 in respiratory samples. The main advantages of antigen tests are that they can provide results in minutes, are simpler than RT-PCR tests to perform, and are sometimes used at the point of care, such as at a health clinic. However, they are not as sensitive as RT-PCR tests, so negative results do not rule out infection.
- Blood Test for Antibodies (Total, IgG, IgM) to SARS-CoV-2 (Serology): These tests detect antibodies produced by the body's immune system in response to SARS-CoV-2. COVID-19 serology tests can tell whether or not you have had the viral infection in the past. However, antibody tests are not the preferred tests to diagnose current infections. Antibodies don’t show up for about 1 to 2 weeks after you first become sick so antibody tests could miss some early infections. (For more general information on antibodies, also called immunoglobulins, see the article on Immunoglobulins.)
How is the sample collected for testing?
Proper collection of the appropriate samples is essential for accurate COVID-19 test results.
- For RT-PCR or Antigen Testing: The preferred sample is a swab from the back of your nose. This is called a nasopharyngeal swab, or NP swab. It is collected by having you tip your head back and then a swab (like a long Q-tip with a small head) is gently inserted through one of the nostrils until resistance is met (about 2 inches). It is left in place for several seconds, then rotated several times and withdrawn. This is not painful, but it may be uncomfortable, cause your eyes to tear and provoke a coughing spell. CDC guidance says that other samples from the respiratory tract may be collected when it is not possible to collect an NP swab. These include a swab from the back of the throat (oropharyngeal swab) or a swab from the front of your nose (nostril). Sometimes a saliva sample may be collected by having the patient spit into a container.
- For Antibody Testing: A blood sample is obtained by inserting a needle into a vein in the arm or by pricking a fingertip and collecting a few drops of blood.
How is the test used?
- COVID-19 RT-PCR and antigen testing may be used to diagnose a SARS-CoV-2 infection and to help make treatment decisions. A test may be used to screen for COVID-19 even if you have no symptoms and/or no known exposure to SARS-CoV-2 so that steps can be taken to prevent spread of the virus to others.
- Antibody (serology) tests may be used to determine if you have been infected with SARS-CoV-2 previously and your body has produced antibodies to the virus, even if you never developed symptoms. Public health officials may use antibody testing to track the extent of the current pandemic. Note that antibody testing is not the preferred test to diagnose current infections. It can take one to two weeks for antibodies to develop after you first become sick, so antibody testing can miss some early infections.
When is it ordered?
COVID-19 RT-PCR or antigen testing:
Diagnostic testing may be ordered when you have signs and symptoms that suggest a SARS-CoV-19 infection, especially if you have been exposed to someone with COVID-19 and/or are at increased risk of infection. Signs and symptoms may include:
- Runny nose, congestion
- Shortness of breath, difficulty breathing
- Chills, sometimes with repeated shaking
- Muscle pain, body aches
- Sore throat
- New loss of taste or smell
- Nausea, vomiting
You may be tested when you don't have signs and symptoms in several situations. Examples include when:
- You have been in close contact (within 6 feet without a mask) with someone diagnosed with COVID-19
- Your healthcare practitioner or public health official recommends it
- You are in an area with a high number of cases and attend a gathering of 10 or more people without wearing a mask or social distancing
- You work or live in a nursing home, especially if there is an outbreak
- You are an essential worker, healthcare worker or first responder, according you employer's guidelines
- You are admitted to the hospital and/or will undergo a medical or surgical procedure
The Centers for Disease Control and Prevention (CDC) provides guidance about who should be tested, but testing decisions are ultimately made by healthcare practitioners and the state and local health departments. Most people have a mild to moderate illness and can recover at home regardless of a test result, and staying home to recover may be safer for these individuals and their healthcare providers than going to a testing site to be tested. However, testing results may be helpful to inform decision-making about whether or not you should stay home and away from other people, stay home from work and/or inform close contacts, for example.
The CDC is regularly updating guidelines as to who is a priority for testing. You can find the current information at the CDC's webpage Test for Current Infection.
Antibody (serology) testing
The blood test for antibodies may be ordered when a healthcare practitioner wants to see if your body has developed antibodies to SARS-CoV-2, even if you did not have symptoms. The protocol for who will be tested for antibodies may change as more serology tests are approved by the FDA and become available.
What does the test result mean?
- A positive PCR-RT test means that it’s very likely that you have COVID-19 and are presumed to be contagious. The result can't tell you when you were infected or how severe your symptoms are likely to be.
- A negative PCR-RT test means it is likely you are not infected at the time of the test. However, you can still become infected later. If you currently have respiratory symptoms, a negative result may mean that you have something other than COVID-19 (e.g., influenza). Another possibility is that there is not enough SARS-CoV-2 virus in the specimen to be detected. This may be due to either a poor sample collection or because it’s too early in an infection to detect the virus.
Rapid antigen tests
- A positive result means it is likely you are infected with SARS-CoV-2 and are probably contagious.
- A negative result means you probably don't have COVID-19.
However, rapid antigen tests may miss some infections (false negatives) or may indicate you are infected when, in fact, you are not (false positives). The amount of antigen in a sample may decrease the longer you have symptoms of infection. Respiratory samples collected after you have had symptoms for more than 5 (for some antigens) or more than 7 days (for others) may be more likely to be negative compared to a molecular test. If your antigen test result doesn't fit with your clinical picture (signs, symptoms or recent exposure), then the result may need to be confirmed with an RT-PCR test (the "gold standard" for diagnosing COVID-19).
Antibody (serology) testing
- A positive antibody test means that you were infected with SARS-CoV-2 at one time. At this time, it remains unknown whether the presence of antibodies to SARS-CoV-2 is indicative of protection from re-infection. Studies are on-going to determine whether protective immunity is generated following infection, and if so, for how long such immunity lasts.
- A negative antibody test means that your immune system has not produced antibodies to the infection, which likely means that you have not been infected with SARS-CoV-2 previously. However, you can have a negative antibody test if you are tested too soon after exposure and your body has not yet produced enough antibodies to be detected, or if you are significantly immunocompromised. Also, a small proportion of the infected individuals may not produce antibodies following infection. The CDC says it takes about one to two weeks after you become ill to develop detectable antibodies, and it can take longer in some individuals.
Should I self-quarantine if I am exposed to someone with COVID-19 or if I have respiratory symptoms?
Even if you don't show symptoms or do not get tested, health experts recommend quarantining yourself for 10-14 days if you have been exposed to coronavirus by being in close contact with someone who has been confirmed or suspected to have the disease. You may not know if you have been exposed, but if you start to show respiratory signs or symptoms, you should self-quarantine for 14 days.
If I am infected but don’t have symptoms, can I still spread the virus?
Yes. Some people who have been infected by SARS-CoV-2 don't display any symptoms—they're asymptomatic. However, they can still be contagious and spread the virus to other people (carriers), which is why quarantining is important after you have been exposed to someone with COVID-19, even if you have no symptoms.
Can I test myself for COVID-19 at home?
Yes. The FDA recently issued emergency use authorizations for some COVID-19 tests that can be used for testing yourself at home. Some of these at-home tests detect viral proteins (antigens) in the sample and a few detect the RNA of the virus. They generally provide results within 15 to 30 minutes. While some require a prescription from a doctor, at least one is available without a prescription. To use the antigen tests, the user must first download the appropriate application (app) for a smart phone.
In addition, there are several commercial laboratories that can send collection kits to patients so they can use them to collect a nasal sample at home, and then send the sample back to the lab for a very specific molecular test.
Although home tests can offer many benefits like rapid results, it's also important to recognize the potential tradeoffs between quality and convenience. Errors can arise with any type of home test because of a number of possible mistakes. These range from improper storage to errors in how you collect your sample and perform the test. For more information and tips on home testing, read With Home Testing, Consumers Take Charge of Their Health.
How accurate is the COVID-19 RT-PCR test?
While lab professionals and test developers work to ensure that tests are accurate as possible, no test is 100% perfect. The COVID-19 RT-PCR tests are very specific for the virus, but there is a small chance to get a false-positive (testing positive without being infected with the virus). Additionally, a negative RT-PCR test means you were probably not infected at the time the sample was collected, but there is a possibility that there was a problem with sample collection, storage or transport or that not enough virus was present in the sample to be detected. This could lead to a false negative (testing negative despite being infected with the virus). For more in-depth information, see the article How Reliable is Laboratory Testing?
Should I get a RT-PCR or antigen test a second time or multiple times?
If you have a negative RT-PCR or antigen test and still show symptoms, you may need to be tested a second time. Your healthcare practitioner will decide if it is necessary for you to be retested. Your healthcare practitioner and/or employer may require additional tests depending on the circumstances.
How long does it take to get RT-PCR test results?
The amount of time it takes to get COVID-19 test results varies based on where you get tested. Once swabbed, the specimen gets sent to a lab. Sometimes, the lab is onsite, but often, it must be sent to an outside laboratory for processing. There may be a backlog of tests, increasing the amount of time it takes to get results. Therefore, you may get your tests results as quickly as within 24 hours, or it may take between five and 10 days.
What happens if I test positive for the virus?
If you test positive, you need to take several steps to keep the SARS-CoV-2 virus from spreading to others in your home and community:
- Stay home, unless it's to get medical care. Ask others to take care of needs such as grocery shopping.
- Stay in touch with your doctor and monitor your symptoms. If your symptoms get worse, call your doctor.
- If you have trouble breathing or other severe symptoms, seek medical care immediately.
- Stay away from others in your home and use a separate bathroom if possible.
- Cover coughs and sneezes with a tissue or with your elbow. Wash your hands thoroughly with soap and water, and often.
- Areas and surfaces in your home should be cleaned and disinfected often. The areas where you are isolated should be cleaned every day. (See the CDC's resource on Cleaning and Disinfection for Households.)
- If you will be visiting your doctor, call ahead first so they can protect others who may not have the virus by giving you a mask and your own area to wait.
More details can be found at the CDC's COVID-19 resource, Caring for Yourself at Home.
If I have a positive RT-PCR or antigen test, should my family or household members be tested?
How is COVID-19 treated?
There is no antiviral treatment available for COVID-19. Treatment is mainly supportive to help relieve symptoms. This may include pain relievers, such as acetaminophen, cough syrup or medication, getting rest and drinking enough fluids to stay hydrated. Serious illness may require treatment in the hospital and supplemental oxygen. If you develop serious symptoms, such as difficulty breathing, seek medical attention immediately.
Researchers are investigating additional treatment options, including drugs used to treat other conditions, antiviral drugs that were developed for other viruses, and plasma containing antibodies, known as convalescent plasma, from people who have recovered from COVID-19.