Self-tests that you can buy in shops are antigen tests. This is especially likely if virus levels are low, such as very early after the onset of symptoms. This means that the test will give a false negative result more often. Because there is no amplification of the signal as in the PCR test, an antigen test is less sensitive. The result is usually visible about fifteen minutes after applying the sample to the test set. The antigen test (or self-test) is a rapid test. Antigens are proteins on the exterior surface of the virus that can produce an immune response in the body (in contrast to the genetic material in the virus). The antigen test (or self-test) detects the presence of antigens for SARS-CoV-2 in nasal and/or throat mucus. As a result, they can complement each other in this respect, rather than competing if supplies become scarce. The LAMP test requires different equipment and chemical substances than are needed for PCR tests. Therefore, this test is faster than the PCR test, which requires fluctuations in temperature. The major advantage of the LAMP test is that the fragments of genetic material are replicated at only one temperature. However, the method used for that purpose in the LAMP test is completely different from the PCR test. The LAMP (loop-mediated isothermal amplification) test is a form of testing in which small fragments of genetic material are copied or replicated, similar to the PCR test. That is why a TMA test cannot be used to determine the Ct value. A TMA test uses a different measuring method than the PCR, expressed in Relative Light Units (RLU). A TMA test also detects the presence of amplified genetic material from SARS-CoV-2. TMA testįor a TMA (Transcription Mediated Amplification) test, a sample is taken using the same method as the PCR test, and then processed in a laboratory. That is why a PCR test result always takes a little longer (at least a few hours). A lower Ct value means that there is more virus present in the specimen. If the virus is present in higher levels, it will take fewer amplification cycles to reach that cycle threshold. The ‘Cycle threshold’ or Ct value is the number of amplification cycles required to detect the first signal that the virus is present. During each cycle, the genetic material doubles in volume this continues until it is detected by the PCR device. The genetic material is copied in different rounds or ‘cycles’. That means that the test cannot give a positive result for other viruses, such as those that cause the flu or the common cold. This fragment of genetic material is specific to the SARS-CoV-2 virus. To ensure that the test will be as sensitive as possible, a specific fragment of the genetic material is amplified (copied) using the polymerase chain reaction method, known as PCR.
That means that the PCR test also detects the virus in someone who has a low viral load, either because they are not carrying much of the virus yet, or they no longer have much virus left in their body. That is why the PCR test has a high test sensitivity. In the PCR test, a small fragment of genetic material inside the virus is replicated repeatedly, in order to detect the presence of the virus even in very small quantities. This sample goes to a laboratory, where research is done to check for the presence of the SARS-CoV-2 virus. To perform this test, a smear is taken from the nose and throat with a cotton swab. The PCR test detects specific fragments of genetic material from the coronavirus SARS-CoV-2. The polymerase chain reaction test or “PCR test”
Due to the testing technique, the tests in the NAAT category are generally more sensitive than the rapid antigen tests (which includes self-tests). The category of tests known as NAAT (Nucleic Acid Amplification Test) includes the PCR test, the TMA test and the LAMP test. Which types of COVID-19 tests are there, and what do they tell us? NAAT category Various types of tests have been used over the past few years to detect a SARS-CoV-2 infection.
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