General Question

COVID-19 testing is now a regular part of life for many individuals across the country. As the Omicron variant emerges as the dominating strain of the SARS-CoV-2 virus, the unvaccinated and vaccinated alike are relying more and more on weekly (sometimes daily) tests to work, travel, or generally engage with the community. Horizon Laboratories is dedicated to offering our patients the best healthcare options available. As of January 2022, there are two broad categories of testing available to the public: PCR tests and antigen tests. They are both considered ‘diagnostic tests,’ which means either will be able to tell you if you are currently infected with the coronavirus at the time of testing. While department of health guidelines on isolation and/or quarantine will continue to evolve, understanding how these tests work is information to be aware of. A lot of our patients want to understand: What is the difference between PCR and antigen tests?

According to Harvard Medical School: “Antigen tests detect specific proteins on the surface of the coronavirus. They are sometimes referred to as rapid diagnostic tests because it can take less than an hour to get the test results. Positive antigen test results are highly specific, meaning that if you test positive you are very likely to be infected.” Antigen tests, while offering results within 15-30 minutes with great accuracy, can return a higher rate of false negatives than the PCR test. Once infected, a patient ‘sheds’ the viral load in their system; these levels can vary widely over the course of infection. Test too early (or too late) and it may result in a false negative – but, antigen tests will detect active infection. Antigen testing is still widely regarded as the primary line of defense because they offer results in minutes, doesn’t require laboratory processing, and costs less out-of-pocket. we can even perform antigen tests at home or at Events.

“A polymerase chain reaction (PCR) test is performed to detect genetic material from a specific organism, such as a virus. The test detects the presence of a virus if you are infected at the time of the test. The test could also detect fragments of the virus even after you are no longer infected.” PCRs determine whether the virus is present by looking for the presence of the virus’s genetic material. Most of the time, PCR tests are extremely accurate; the only drawback being the amount of time between getting tested and getting a definitive answer. After a sample is extracted (commonly using the deep nasal swab technique, although samples from the throat or saliva may be tested also), it’s sent to a laboratory for processing. Typically, that process lasts anywhere from 2-24 hours. We’re pleased to offer PCR testing with results in 2-24 Hours.

Generally, the differences are technique, time, and usage. The cost often varies too. An antigen test is a rapid test, while the PCR test traditionally takes a few hours to return results. An antigen test looks for specific proteins found on the surface of the virus, while a PCR test seeks out and amplifies the presence of the virus’s DNA material. PCR tests are preferred/required for international travel. Our price for an antigen test is R350; for PCR, the test starts from R500 – R1200 We offer both PCR and antigen tests at Horizon Laboratories.

PCR tests and antigen tests are both diagnostic tests, which means that they can be used to determine whether you currently have an active coronavirus infection. However, there are important differences between these two types of tests. PCR tests detect the presence of the virus’s genetic material using a technique called reverse transcriptase polymerase chain reaction, or RT-PCR. For this test, a sample may be collected through a nasal or throat swab, or a saliva sample may be used. The sample is typically sent to a laboratory where coronavirus RNA (if present) is extracted from the sample and converted into DNA. The DNA is then amplified, meaning that many copies of the viral DNA are made, in order to produce a measurable result. The accuracy of any diagnostic test depends on many factors, including whether the sample was collected properly, when during the course of illness the testing was done, and whether the sample was maintained in appropriate conditions while it was shipped to the laboratory. Generally speaking, PCR tests are highly accurate. Antigen tests detect specific proteins on the surface of the coronavirus. They are sometimes referred to as rapid diagnostic tests because it can take less than an hour to get the test results. Positive antigen test results are highly specific, meaning that if you test positive you are very likely to be infected. However, there is a higher chance of false negatives with antigen tests, which means that a negative result cannot definitively rule out an active infection. If you have a negative result on an antigen test, your doctor may order a PCR test or a second rapid antigen test to confirm the result. It may be helpful to think of a COVID antigen test as you would think of a rapid strep test or a rapid flu test. A positive result for any of these tests is likely to be accurate, and allows diagnosis and treatment to begin quickly, while a negative result often results in further testing to confirm or overturn the initial result.

Two types of diagnostic tests are currently available in the US. PCR tests detect viral RNA. Antigen tests, also called rapid diagnostic tests, detect specific proteins on the surface of the coronavirus. Antigen test results may come back in as little as 15 to 45 minutes; you may wait several days for PCR test results. The accuracy of any diagnostic test depends on many factors, including whether the sample was collected properly. For PCR tests, which are typically analyzed in a laboratory, test results may be affected by the conditions in which the test was shipped to the laboratory. Results may also be affected by the timing of the test. For example, if you are tested on the day you were infected, your test result is almost guaranteed to come back negative, because there are not yet enough viral particles in your nose or saliva to detect. The chance of getting a false negative test result decreases if you are tested a few days after you were infected, or a few days after you develop symptoms. Generally speaking, if a test result comes back positive, it is almost certain that the person is infected. A negative test result is less definite. There is a higher chance of false negatives with antigen tests, and early data suggests that antigen tests may be even more likely to miss the Omicron variant. If you have a negative result on an antigen test, your doctor may order a PCR test or recommend a second rapid antigen test to confirm the result. If you experience COVID-like symptoms and get a negative PCR test result, there is no reason to repeat the test unless your symptoms get worse. If your symptoms do worsen, call your doctor or local or state healthcare department for guidance on further testing. You should also self-isolate at home. Wear a mask when interacting with members of your household. And practice physical distancing

A serologic test is a blood test that looks for antibodies to SARS-CoV-2 created by your immune system in response to infection or vaccination. Your body takes one to three weeks after you have acquired the infection to develop antibodies to this virus. For this reason, serologic tests are not sensitive enough to accurately diagnose an active COVID-19 infection, even in people with symptoms.

When a person gets or is vaccinated against a viral or bacterial infection, a healthy immune system makes antibodies against one or more components of the virus or bacterium. The COVID-19 coronavirus contains ribonucleic acid (RNA) surrounded by a protective layer, which has spike proteins on the outer surface that can latch on to certain human cells. Once inside the cells, the viral RNA starts to replicate and also turns on the production of proteins, both of which allow the virus to infect more cells and spread throughout the body, especially to the lungs. While the immune system could potentially respond to different parts of the virus, it’s the spike proteins that get the most attention. Immune cells recognize the spike proteins as a foreign substance and begin producing antibodies in response. There are two main categories of antibodies: Binding antibodies. These antibodies can bind to either the spike protein or a different protein known as the nucleocapsid protein. Binding antibodies can be detected with blood tests starting about one week after the initial infection. If antibodies are found, it’s extremely likely that the person has been infected with the COVID-19 coronavirus. The antibody level declines over time after an infection, sometimes to an undetectable level. Binding antibodies help fight the infection, but they might not offer protection against getting reinfected in the future. It depends on whether they are also neutralizing antibodies. Neutralizing antibodies. The body makes neutralizing antibodies that attack the coronavirus’s spike protein, making it more difficult for the virus to attach to and enter human cells. Neutralizing antibodies provide more lasting protection than binding antibodies against reinfection. Monoclonal antibodies are manmade versions of neutralizing antibodies. The FDA has authorized monoclonal antibody treatments for certain groups of COVID-19 patients.

The immune system responds to COVID-19 infection by stimulating white blood cells called lymphocytes to form antibodies that fight the infection. These antibodies and lymphocytes retain a temporary protective effect against reinfection. But it is only temporary. There have been many confirmed cases of reinfection with COVID-19. In other words, a person got sick with COVID-19, recovered, and then became infected again. This has been especially true as the coronavirus has mutated into COVID-19 variants. There was a rise in reinfections with the Delta variant, and an explosive increase in the reinfection rate due to the Omicron variant. Omicron has about 50 mutations, including more than 30 mutations on the spike protein, the region of the virus that our immune systems recognize after previous infection. Because of this, Omicron is more capable than previous variants of evading our immune defenses and causing reinfection. We have learned that vaccination plus a booster dose strengthens the natural immune response, even in those who have been previously infected, and further reduces the risk of reinfection. Although breakthrough infections after vaccination are also more common with Omicron than previous variants, vaccination continues to protect well against severe illness. The bottom line? Get vaccinated and boosted whether or not you’ve already had COVID-19.

The time from exposure to symptom onset (known as the incubation period) is thought to be two to 14 days. Symptoms typically appeared within five days for early variants, and within four days for the Delta variant. The incubation period appears to be even shorter – about three days – for the Omicron variant. We know that people tend to be most infectious early in the course of their infection. With Omicron, most transmission occurs during the one to two days before onset of symptoms, and in the two to three days afterwards. Wearing masks, particularly indoors, can help reduce the risk that someone who is infected but not yet experiencing symptoms may unknowingly infect others.

“Without symptoms” can refer to two groups of people: those who eventually do have symptoms (pre-symptomatic) and those who never go on to have symptoms (asymptomatic). During this pandemic, we have seen that people without symptoms can spread the coronavirus infection to others. A person with COVID-19 may be contagious 48 hours before starting to experience symptoms. In fact, people without symptoms may be more likely to spread the illness, because they are unlikely to be isolating and may not adopt behaviors designed to prevent spread. But what about people who never go on to develop symptoms? A study published in JAMA Network Open found that almost one out of every four infections may be transmitted by individuals with asymptomatic infections. The proportion of asymptomatic transmission appears to be even higher with the Omicron variant. Getting vaccinated and boosted once you are eligible is important for protecting not just yourself but others as well; evidence suggests that you’re less likely to infect others, or may be contagious for a shorter period of time, once you’ve been vaccinated.

People are thought to be most contagious early in the course of their illness. With Omicron, most transmission appears to occur during the one to two days before onset of symptoms, and in the two to three days afterwards. People with no symptoms can also spread the coronavirus to others. By the 10th day after COVID symptoms begin, most people will no longer be contagious, as long as their symptoms have continued to improve and their fever has resolved. People who test positive for the virus but never develop symptoms over the following 10 days after testing are also probably no longer contagious. According to the CDC’s isolation guidelines, everyone who tests positive for COVID-19 should isolate at home for five days if you have no symptoms or your symptoms are improving after five days, you can discontinue isolation and leave your home continue to wear a mask around others for five additional days. If you have a fever, continue to isolate at home until you no longer have a fever. You can use the CDC’s Quarantine and Isolation calculator to help determine when and how long you should stay home, get tested, and wear a mask around others if you have COVID-19 or were recently in close contact with someone who tested positive for COVID-19.

Yes, you can. That’s why the CDC recommends that everyone who tests positive for COVID-19 should isolate from others for at least five days, regardless of their vaccination status.


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