COVID-19 Tests: PCR, Rapid Antigen, and Antibody Tests – What’s the Difference?
During the COVID-19 pandemic, the importance of reliable, fast, and accessible testing has become especially clear. The ability to detect SARS-CoV-2 infection in a timely manner allows people to make responsible decisions—self-isolate, protect loved ones, and help reduce the spread of the virus.
COVID-19 tests are divided into PCR (molecular), rapid antigen, and antibody (serological) tests. Each serves a different purpose, uses different sample types, and helps answer different questions about infection or immunity.
The main tests used to detect and assess COVID-19 infection include:
Polymerase Chain Reaction (PCR) tests – laboratory-based tests designed to detect an active SARS-CoV-2 infection.
Rapid antigen tests – allow on-site detection of COVID-19 infection but are less sensitive than PCR tests.
Antibody (serological) tests – do not detect active infection but indicate whether the body has previously encountered the virus and developed an immune response.
PCR testing is considered the gold standard for COVID-19 diagnosis. This method directly detects viral RNA, which appears in the body before antibodies form or symptoms develop.
During a PCR test, viral genetic material from a nasopharyngeal sample is amplified in a laboratory using specific enzymes—reverse transcriptase and DNA polymerase. This process allows even very small amounts of the virus to be detected.
According to Dr. Edward Wright, Senior Lecturer in Microbiology at the University of Sussex, PCR tests make it possible to accurately identify infected individuals, isolate them, and effectively break chains of transmission.
high sensitivity,
ability to detect infection at an early stage,
essential for public health surveillance.
samples must be sent to a laboratory,
longer turnaround time (from several hours to several days),
potential for false-negative or false-positive results.
Rapid antigen tests are also designed to detect active COVID-19 infection, but instead of viral RNA, they identify specific SARS-CoV-2 proteins (antigens).
During testing, a nasal or nasopharyngeal sample is placed onto a test cassette. If viral antigens are present, a visible colored line appears.
results available within 15–30 minutes,
can be performed on-site or at home,
no laboratory equipment required,
lower cost.
lower sensitivity compared to PCR tests,
particularly limited accuracy in asymptomatic individuals.
Systematic reviews indicate that the average sensitivity of antigen tests is about 72% in symptomatic individuals and 58% in asymptomatic individuals. Therefore, a negative result does not necessarily mean that a person is not infected.
Antibody (serological) tests are used not to diagnose active infection, but to determine whether the body has previously been exposed to SARS-CoV-2.
Antibodies typically appear in the blood 1–2 weeks after infection. Studies show that even after mild COVID-19, antibodies may persist for several months or longer.
Antibody tests are also used for:
assessing immune response after vaccination,
epidemiological studies,
population-level immunity analysis.
It is important to emphasize that antibody tests are not intended to diagnose active COVID-19 infection.
Different tests require different sample types:
Anterior nasal swabs – most commonly used for rapid antigen tests.
Mid-turbinate or nasopharyngeal swabs – used for PCR tests.
Saliva samples – used in some diagnostic tests.
Blood samples – used for antibody testing.
Fast and reliable testing allows for:
timely isolation of infected individuals,
reduction of virus transmission,
protection of vulnerable groups,
informed decisions regarding work, travel, and treatment.
While rapid antigen tests can be useful for screening purposes, laboratory-based PCR tests remain the most accurate.
COVID-19 tests play different but complementary roles:
PCR tests – the most accurate method for detecting active infection.
Rapid antigen tests – a quick solution for everyday situations, but with limited accuracy.
Antibody tests – provide information about past infection or immune response but do not diagnose COVID-19.
When choosing a test, it is important to consider the purpose of testing, the presence of symptoms, and the manufacturer’s recommendations.
