What You Need to Know: COVID-19, PCR Testing (PCR Test), and Rapid Antigen Tests
A nasopharyngeal swab performed using a PCR test for the detection of COVID-19 is one of the most accurate and reliable methods for diagnosing COVID-19 infection. A positive PCR test result means that it is very likely you are infected with COVID-19. A negative result indicates that, at the time of testing, you were most likely not infected with the COVID-19 virus.
Testing is recommended if you are experiencing symptoms of COVID-19 or have had contact with a person whose COVID-19 test result was positive.
PCR stands for polymerase chain reaction. It is a laboratory testing method used to detect the genetic material of a specific organism, such as a virus. A PCR test can identify the presence of a virus in the body at the time the test is performed. Due to its extremely high sensitivity, this method can also detect viral fragments even after an active infection has already resolved.
A PCR test for COVID-19 is a molecular test that analyzes a sample taken from the upper respiratory tract. The test looks for the genetic material of the SARS-CoV-2 virus—ribonucleic acid (RNA).
In the laboratory, PCR technology allows very small amounts of viral RNA to be converted into deoxyribonucleic acid (DNA) and amplified until the virus can be detected, if present in the sample. For this reason, the PCR test has been considered the gold standard for COVID-19 diagnosis since its authorization in February 2020. It is an extremely accurate and reliable diagnostic method.
Your healthcare professional may recommend a COVID-19 test if you experience one or more of the following symptoms:
fever or chills
cough
shortness of breath or difficulty breathing
fatigue
muscle or body aches
headache
new loss of taste or smell
sore throat
nasal congestion or runny nose
nausea or vomiting
diarrhea
It is important to note that not everyone with COVID-19 experiences symptoms, and symptom severity can vary widely. If you feel unwell during the pandemic, it is recommended to consult a healthcare professional even if you have been vaccinated.
A COVID-19 PCR test consists of three main stages:
A healthcare professional collects a respiratory sample from the nose or nasopharynx using a special swab. The swab is soft, long, and flexible. Different types of swabs are used, including shallow nasal swabs and deeper nasopharyngeal swabs. Both methods are suitable for COVID-19 PCR testing. After collection, the swab is securely sealed in a tube and sent to a laboratory.
In the laboratory, viral genetic material is extracted from the sample and separated from other components.
During this stage, special enzymes, chemical reagents, and a PCR machine called a thermal cycler are used. With each heating and cooling cycle, the target genetic material is amplified. After many cycles, millions of copies of SARS-CoV-2 genetic material are present in the tube. If the virus is present, one of the reaction components emits a fluorescent signal, which the machine detects and interprets as a positive test result.
A positive result means that you are likely infected with the SARS-CoV-2 virus. This may represent an asymptomatic infection or COVID-19 illness if symptoms are present. Most people experience mild disease and can safely recover at home. If symptoms worsen or you have concerns, you should contact a healthcare professional.
A negative result indicates that, at the time the sample was collected, you were most likely not infected. However, this does not guarantee the absence of infection—early-stage infection or testing after recovery may result in a false-negative result. In addition, you may become infected after testing and potentially spread the virus to others.
In most cases, COVID-19 PCR test results are available within 24 hours of sample collection. In some situations, results may take several days, depending on laboratory workload and sample transportation time.
Due to its high sensitivity, a PCR test can detect viral fragments even after recovery, when a person is no longer infectious. As a result, the test may remain positive for some time after illness. In individuals with weakened immune systems, viral shedding may last longer. If your PCR test is positive but you believe you have already recovered, it is recommended to consult a healthcare professional.
Two main types of tests are used to diagnose COVID-19:
PCR test – detects the genetic material of the virus or its fragments. It is the most accurate and reliable method for identifying active infection.
Rapid antigen test – detects proteins (antigens) found on the surface of the virus. The test is performed quickly, usually within 15–30 minutes, and is most accurate during the first few days of symptoms, when the viral load is highest.
The PCR test is more sensitive and accurate than the rapid antigen test. If a rapid antigen test result is negative but symptoms or high-risk exposure are present, a PCR test is often recommended to confirm the result.
