COVID-19 Test: Types, How They Work & When to Test

What Are the Different Types of COVID-19 Tests?

There are three main types of COVID-19 tests: PCR tests (molecular tests) that detect viral genetic material with high accuracy, rapid antigen tests that detect viral proteins and give results in 15-30 minutes, and antibody tests that detect past infection. PCR tests are considered the gold standard for diagnosis.

Understanding the different types of COVID-19 tests is crucial for knowing which test to use and when. Each type of test has specific advantages, limitations, and appropriate use cases. The choice of test depends on factors such as the reason for testing, how quickly you need results, and whether you're symptomatic.

COVID-19 diagnostic tests work by detecting either the virus itself or the body's immune response to it. Diagnostic tests (PCR and antigen tests) identify active infections, while antibody tests indicate previous infection. The accuracy and timing of these tests vary significantly, which affects their reliability in different situations.

Healthcare systems worldwide have developed testing strategies that combine different test types to maximize detection while managing resources effectively. Understanding these tests helps you make informed decisions about when and how to get tested, and how to interpret your results correctly.

PCR Tests (Molecular Tests)

Polymerase Chain Reaction (PCR) tests, also called molecular tests or nucleic acid amplification tests (NAATs), are the most accurate method for detecting active COVID-19 infection. These tests work by detecting the genetic material (RNA) of the SARS-CoV-2 virus. The sample, usually collected via a nasal or throat swab, is sent to a laboratory where the viral RNA is amplified millions of times to detectable levels.

PCR tests have a sensitivity of approximately 95-99% in symptomatic individuals, meaning they correctly identify almost all people who are infected. The specificity is also extremely high (over 99.9%), so false positive results are very rare. However, PCR tests can remain positive for weeks or even months after infection, even when a person is no longer contagious. This is because the test can detect fragments of viral RNA that remain in the body after the active infection has cleared.

The main disadvantage of PCR tests is the turnaround time. Results typically take 24-72 hours because samples must be processed in specialized laboratories with trained personnel and sophisticated equipment. In some cases, especially during high-demand periods, results may take even longer.

Rapid Antigen Tests

Rapid antigen tests detect specific proteins on the surface of the SARS-CoV-2 virus, rather than its genetic material. These tests provide results in just 15-30 minutes and can be performed at point-of-care locations or at home without laboratory processing. The convenience and speed of antigen tests make them valuable for screening purposes and situations requiring quick results.

While antigen tests are less sensitive than PCR tests, their accuracy varies depending on the testing context. In symptomatic individuals tested within the first week of illness, antigen tests have sensitivity of approximately 80-90%. However, in asymptomatic individuals, sensitivity drops to around 50-60%, meaning they may miss about half of infections. The specificity remains high (over 99%), so positive results are reliable indicators of infection.

The lower sensitivity of antigen tests means that a negative result does not definitively rule out infection, particularly in people without symptoms or very early in the infection when viral loads may be low. For this reason, guidelines often recommend confirming negative antigen tests with PCR testing in high-risk situations or when there is a strong suspicion of infection.

Antibody Tests (Serology Tests)

Antibody tests, also known as serology tests, detect antibodies produced by the immune system in response to SARS-CoV-2 infection. These tests are not useful for diagnosing active infection because antibodies typically take 1-3 weeks to develop after infection. Instead, antibody tests are used to determine whether someone has been previously infected with COVID-19.

Antibody tests can detect different types of antibodies, including IgM (which appears early in infection) and IgG (which appears later and may provide longer-lasting immunity). These tests have applications in research, epidemiological studies, and assessing population-level immunity. However, they are not recommended for diagnosing current illness or for making isolation decisions.

When Should You Take a COVID-19 Test?

You should take a COVID-19 test if you have symptoms (fever, cough, loss of taste/smell), 5 days after close contact with an infected person, before visiting high-risk individuals, or as required for travel or work. Testing when symptomatic provides the most accurate results, especially with rapid antigen tests.

The timing of COVID-19 testing significantly affects the accuracy of results. Understanding when to test helps ensure you get reliable results and can take appropriate action to protect yourself and others. Different situations call for different testing strategies, and the optimal timing varies based on whether you have symptoms or are testing after exposure.

Testing too early after exposure is a common mistake that leads to false negative results. The SARS-CoV-2 virus needs time to replicate to detectable levels after initial infection. During this incubation period, which typically lasts 2-5 days, tests may not detect the virus even if you are infected. This is why guidelines recommend waiting until day 5 after exposure for the most accurate results.

For people with symptoms, immediate testing is recommended regardless of when exposure may have occurred. Symptoms indicate that the virus has replicated to levels that are usually detectable by both PCR and antigen tests. Testing at symptom onset also helps ensure timely isolation and treatment if needed.

Testing After Exposure

If you have been in close contact with someone who tested positive for COVID-19, the recommended approach is to test on day 5 after exposure. Close contact is generally defined as being within 6 feet (2 meters) of an infected person for a cumulative total of 15 minutes or more over a 24-hour period. This waiting period allows the virus to replicate to detectable levels if transmission occurred.

If you test negative on day 5 but develop symptoms later, you should test again immediately. Some experts recommend serial testing, such as testing on days 3 and 5 after exposure, to increase the likelihood of detecting infection. If using rapid antigen tests after exposure, consider repeating the test in 24-48 hours if the first result is negative, as this can improve detection rates.

During the waiting period before testing, it is advisable to wear a well-fitting mask around others, avoid contact with high-risk individuals, and monitor yourself for symptoms. These precautions help reduce potential transmission during the period when you might be infected but not yet testing positive.

Testing With Symptoms

If you develop symptoms consistent with COVID-19, you should test as soon as possible. Common symptoms include fever, cough, shortness of breath, fatigue, muscle aches, headache, new loss of taste or smell, sore throat, congestion, nausea, and diarrhea. Both PCR and rapid antigen tests perform well in symptomatic individuals, particularly during the first week of illness.

Testing during the symptomatic phase provides the most accurate results because viral loads are typically at their highest during this period. Even rapid antigen tests, which are less sensitive overall, have good detection rates in symptomatic individuals. If your initial test is negative but you continue to have symptoms, consider repeating the test after 24-48 hours or obtaining a PCR test for confirmation.

Testing for Travel, Work, or Events

Many countries, employers, and event organizers have established testing requirements. If testing is required for these purposes, follow the specific guidelines provided, including the timing of when tests must be taken (often within 24-72 hours of the activity). PCR tests are sometimes required for international travel due to their higher sensitivity, while antigen tests may be accepted for other situations.

How Do You Properly Use a COVID-19 Home Test?

To use a COVID-19 home test correctly: wash your hands, read all instructions, collect the sample by inserting the swab 2-3 cm into each nostril and rotating 5 times, place the swab in the buffer solution, apply drops to the test device, wait 15-20 minutes (not longer than 30), and read the results. Two lines mean positive, one control line means negative.

Proper technique is essential for accurate home COVID-19 test results. Studies have shown that user error is one of the main reasons for false negative results with home tests. Taking the time to understand and follow the correct procedure increases the reliability of your results and helps you make informed decisions about isolation and seeking medical care.

Before starting the test, gather all materials and read the instructions completely. Different test brands may have slightly different procedures, buffer solutions, or timing requirements. Using the test at room temperature is important, as extreme temperatures can affect the chemical reactions that produce results. Make sure your hands are clean before handling the test components to avoid contamination.

The sample collection technique is particularly important. The swab must be inserted deep enough into the nostril (typically about 2-3 cm or 1 inch) to collect cells from the nasal mucosa, where the virus resides. Simply swabbing just inside the nose will not collect an adequate sample. Rotating the swab against the nasal wall helps dislodge and collect cells. Most tests require swabbing both nostrils to maximize sample collection.

Step-by-Step Instructions

Begin by washing your hands thoroughly with soap and water for at least 20 seconds. Remove all test components from the packaging and lay them out on a clean, flat surface. Check that nothing appears damaged and verify the test has not expired. If included, prepare the extraction tube by adding the buffer solution according to the instructions.

For sample collection, tilt your head back slightly and insert the swab about 2-3 cm (approximately 1 inch) into one nostril. You should feel slight resistance when you reach the nasopharynx. Rotate the swab against the nasal wall 5 times while applying gentle pressure. Without setting down the swab, repeat this process in the other nostril using the same swab. Both nostrils should be swabbed to ensure adequate sample collection.

After collecting the sample, immediately insert the swab into the extraction tube containing the buffer solution. Rotate and squeeze the swab against the sides of the tube at least 6 times to release the collected sample into the solution. Leave the swab in the solution for the time specified in the instructions, then squeeze the tube while removing the swab to extract as much liquid as possible.

Cap the extraction tube with the dropper tip provided and apply the specified number of drops (usually 2-4) to the sample well on the test device. Start your timer immediately. Wait the exact time specified in the instructions (typically 15-20 minutes) before reading the results. Do not read results after 30 minutes, as this can lead to inaccurate interpretation.

Reading and Interpreting Results

COVID-19 home tests display results through colored lines that appear in designated regions. Two lines appearing, even if one is faint, indicate a positive result. The line closer to the sample well typically appears first (control line, marked C), followed by the test line (marked T) if positive. Any visible test line, regardless of intensity, should be interpreted as positive.

A single line in the control region indicates a negative result. If no control line appears, the test is invalid regardless of whether a test line is present. Invalid tests should be discarded and repeated with a new test kit. Common causes of invalid results include insufficient sample, not waiting long enough for results to develop, or test kit defects.

How Accurate Are COVID-19 Tests?

PCR tests have 95-99% sensitivity and over 99.9% specificity, making them the gold standard for COVID-19 diagnosis. Rapid antigen tests have 80-90% sensitivity in symptomatic individuals but only 50-60% in asymptomatic people. A positive antigen test is highly reliable (over 99% specificity), but negative results should be interpreted with caution.

Test accuracy is measured using two key metrics: sensitivity and specificity. Sensitivity refers to the test's ability to correctly identify people who are infected (true positive rate). A test with high sensitivity will miss few infections. Specificity refers to the ability to correctly identify people who are not infected (true negative rate). A test with high specificity will produce few false positive results.

Understanding these concepts is crucial for interpreting test results correctly. A highly sensitive test is ideal for ruling out infection, while a highly specific test is better for confirming infection. The practical implications differ depending on which metric is stronger for a given test type.

Beyond inherent test characteristics, accuracy is influenced by timing of testing, sample collection technique, viral load at time of testing, and storage and handling of samples or test kits. A perfectly accurate test can still produce incorrect results if the sample is collected improperly or if testing occurs too early or too late in the infection course.

PCR Test Accuracy

PCR tests represent the gold standard for COVID-19 diagnosis because of their exceptional accuracy. With sensitivity of 95-99% in properly collected samples from symptomatic individuals, these tests detect almost all active infections. The specificity exceeds 99.9%, meaning false positive results are extremely rare.

However, PCR tests are not perfect. False negatives can occur if the sample is collected before viral loads reach detectable levels, if the sample collection technique is inadequate, or if there are technical issues during laboratory processing. False negatives are most common in the first 1-4 days after exposure, before the virus has replicated sufficiently.

A unique characteristic of PCR tests is their ability to detect viral RNA for extended periods after the active infection has resolved. This can result in positive tests for weeks or even months after recovery, even when the person is no longer contagious. For this reason, PCR tests are not recommended for determining when to end isolation or for repeated testing in people with recent infection.

Rapid Antigen Test Accuracy

Rapid antigen tests have lower sensitivity than PCR tests, but their accuracy varies significantly based on testing context. In symptomatic individuals tested within the first week of illness, sensitivity ranges from 80-90%. This means antigen tests will correctly identify 80-90% of infected symptomatic people.

In asymptomatic individuals, sensitivity drops to approximately 50-60%. This lower performance occurs because asymptomatic people often have lower viral loads, producing insufficient antigen for detection. Serial testing (testing multiple times over several days) can improve detection rates in this population.

The specificity of antigen tests remains high (over 99%), meaning positive results are very reliable. When you test positive on an antigen test, you almost certainly have COVID-19. This high specificity makes antigen tests valuable for confirming infection despite their lower sensitivity.

What Should You Do If Your Test Is Positive?

If your COVID-19 test is positive: isolate yourself immediately to prevent spreading the virus, inform close contacts so they can monitor for symptoms and test, monitor your own symptoms and seek medical care if they worsen, stay hydrated and rest, and follow your local health authority's guidelines for isolation duration and return to normal activities.

Receiving a positive COVID-19 test result requires immediate action to protect others and manage your own health. Regardless of whether you feel sick, a positive test means you are infectious and can spread the virus to others. Taking appropriate steps quickly can prevent transmission to family members, coworkers, and vulnerable individuals in your community.

The first and most important step is isolation. This means physically separating yourself from others, ideally in a separate room if you live with other people. Use a separate bathroom if possible. If you must be around others, wear a well-fitting mask. Avoid sharing personal items such as dishes, towels, and bedding. These measures significantly reduce the risk of household transmission.

Informing your close contacts is an essential public health responsibility. Close contacts are people who spent 15 minutes or more within 6 feet of you during your infectious period, which typically begins 2 days before your symptoms started or 2 days before a positive test if asymptomatic. These individuals should monitor for symptoms and consider testing according to local guidelines.

Managing Symptoms at Home

Most people with COVID-19 experience mild to moderate illness and can recover at home without medical intervention. Focus on supportive care including rest, staying well-hydrated, and using over-the-counter medications to manage symptoms. Fever and pain can be managed with acetaminophen (paracetamol) or ibuprofen. For cough and congestion, cough suppressants, decongestants, and honey can provide relief.

Monitor your symptoms regularly, paying particular attention to warning signs that may indicate worsening illness. Keeping a symptom diary can help you track changes and provide useful information if you need to contact a healthcare provider. Check your temperature twice daily and note any changes in breathing comfort or overall energy levels.

Maintain good nutrition even if you don't feel hungry. Light, easily digestible foods are often better tolerated during illness. Continue taking any prescribed medications for chronic conditions unless advised otherwise by your healthcare provider. If you take medications that suppress the immune system, contact your doctor for specific guidance.

When to Seek Medical Care

While most COVID-19 infections resolve without complications, certain warning signs require immediate medical attention. Contact a healthcare provider if you experience difficulty breathing, persistent chest pain or pressure, confusion or difficulty staying awake, inability to keep fluids down, or bluish discoloration of lips or face. These symptoms may indicate severe illness requiring hospital care.

Certain individuals are at higher risk for severe COVID-19 and should contact their healthcare provider early in the course of illness, even without severe symptoms. High-risk groups include adults over 65, people with chronic conditions such as diabetes, heart disease, lung disease, or kidney disease, immunocompromised individuals, and pregnant women. Early antiviral treatment may be recommended for high-risk patients.

What Does a Negative COVID-19 Test Mean?

A negative COVID-19 test means the virus was not detected in your sample at that moment. However, it doesn't completely rule out infection. Accuracy depends on timing, test type, and sample quality. If you have symptoms or known exposure and test negative, consider retesting in 24-48 hours or getting a PCR test for confirmation.

Interpreting a negative COVID-19 test result requires understanding its limitations. A negative result provides a snapshot in time and indicates that detectable levels of the virus were not present in your sample. This does not guarantee that you are not infected, particularly if you tested early after exposure, have symptoms, or used a less sensitive test type.

The false negative rate varies significantly based on when testing occurs relative to exposure. Testing within the first 1-4 days after exposure frequently produces false negative results because viral replication has not yet reached detectable levels. False negative rates are highest on day 1 after exposure (up to 100%) and decrease gradually, reaching their lowest point around day 8 after exposure or day 3 after symptom onset.

The type of test also affects the reliability of negative results. PCR tests have very low false negative rates when properly timed and collected, making negative PCR results highly reassuring. Rapid antigen tests have higher false negative rates, particularly in asymptomatic individuals, so negative results are less definitive and may require confirmation in certain situations.

When to Retest After a Negative Result

If you tested negative but have symptoms consistent with COVID-19, retesting is recommended. Consider repeating a rapid antigen test 24-48 hours after the initial negative result. Symptoms combined with a negative test often indicate that testing occurred before viral loads became detectable. A second negative test with persistent symptoms may warrant PCR testing for definitive results.

After known exposure without symptoms, a single negative test on day 5 is generally considered reliable for PCR tests. For rapid antigen tests, some guidelines recommend testing on multiple days (such as days 3 and 5) to improve detection rates. If you develop symptoms at any point after a negative test, retest immediately regardless of when the exposure occurred.

During periods of high community transmission, a negative test should be interpreted with additional caution. Continue practicing preventive measures such as wearing masks, maintaining distance, and avoiding high-risk activities for several days after a negative test following exposure. This approach accounts for the possibility of a false negative result.

How Is COVID-19 Testing Different for Children?

COVID-19 testing for children uses the same test types as adults, though sample collection may be modified for comfort. Nasal swabs are commonly used instead of nasopharyngeal swabs. Children often have milder symptoms, which may affect test sensitivity. Parents can assist with home testing, and many pediatric-specific guidelines are available.

Testing children for COVID-19 follows similar principles as testing adults, but several practical considerations may differ. Children may be more anxious about the testing process, so preparation and reassurance are important. Explaining the procedure in age-appropriate terms and allowing the child to see the testing materials beforehand can help reduce anxiety and improve cooperation.

The sample collection technique may be modified for children to improve comfort while maintaining accuracy. Nasal swabs (inserted into the front of the nose) are often preferred over nasopharyngeal swabs (inserted deeper) for children. Home test kits designed for nasal swabs can be used effectively in children with proper technique. For very young children, parents may need to assist with or perform the swab collection.

Children frequently experience milder COVID-19 symptoms than adults, which can affect test interpretation. Because viral loads may be lower in mildly symptomatic children, rapid antigen tests may have reduced sensitivity in this population. If clinical suspicion for COVID-19 is high but an antigen test is negative, consider PCR testing for confirmation.

Testing Young Children and Infants

Testing infants and toddlers presents unique challenges due to their size and limited ability to cooperate. Swabbing technique may need to be adjusted for smaller nasal passages. Having a second adult present to help hold and comfort the child can make the process easier. Some healthcare facilities offer pediatric-specific testing approaches designed to minimize discomfort.

For home testing in young children, parents should carefully review the instructions and practice the motions before attempting sample collection. Positioning the child comfortably, perhaps wrapped in a blanket or held securely, helps ensure a complete sample is obtained. If the child moves significantly during collection, the sample quality may be compromised.