Similarly, the testing recommendation no longer applies to care workers, except in unusual circumstances, such as during an outbreak. In such situations, follow the policy of the care facility where you work. Do you need an EU Digital COVID Certificate? See Government.nl for more information.
Even in an endemic stage, there are still vulnerable people who have a higher risk of serious illness from an infection involving SARS-CoV-2 or another respiratory virus. For that reason, it is still important to take them into account. Follow these recommendations if you have symptoms.
Types of tests
Various types of tests have been used over the past few years to detect a SARS-CoV-2 infection. Which types of COVID-19 tests are there, and what do they tell us?
The category of tests known as NAAT (Nucleic Acid Amplification Test) includes the PCR test, the TMA test and the LAMP 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 polymerase chain reaction test or “PCR test”
The PCR test detects specific fragments of genetic material from the coronavirus SARS-CoV-2. To perform this test, a smear is taken from the nose and throat with a cotton swab. This sample goes to a laboratory, where research is done to check for the presence of the SARS-CoV-2 virus. 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. That is why the PCR test has a high test sensitivity. 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.
What is the Ct value of the PCR test?
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. This fragment of genetic material is specific to the SARS-CoV-2 virus. That means that the test cannot give a positive result for other viruses, such as those that cause the flu or the common cold.
The genetic material is copied in different rounds or ‘cycles’. During each cycle, the genetic material doubles in volume; this continues until it is detected by the PCR device. The ‘Cycle threshold’ or Ct value is the number of amplification cycles required to detect the first signal that the virus is present. If the virus is present in higher levels, it will take fewer amplification cycles to reach that cycle threshold. A lower Ct value means that there is more virus present in the specimen. Amplification takes time for each cycle. That is why a PCR test result always takes a little longer (at least a few hours).
For a TMA (Transcription Mediated Amplification) test, a sample is taken using the same method as the PCR test, and then processed in a laboratory. A TMA test also detects the presence of amplified genetic material from SARS-CoV-2. A TMA test uses a different measuring method than the PCR, expressed in Relative Light Units (RLU). That is why a TMA test cannot be used to determine the Ct value.
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. However, the method used for that purpose in the LAMP test is completely different from the PCR test. The major advantage of the LAMP test is that the fragments of genetic material are replicated at only one temperature. Therefore, this test is faster than the PCR test, which requires fluctuations in temperature. The LAMP test requires different equipment and chemical substances than are needed for PCR tests. As a result, they can complement each other in this respect, rather than competing if supplies become scarce.
The antigen test (or self-test)
The antigen test (or self-test) detects the presence of antigens for SARS-CoV-2 in nasal and/or throat mucus. 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) is a rapid test. The result is usually visible about fifteen minutes after applying the sample to the test set. Because there is no amplification of the signal as in the PCR test, an antigen test is less sensitive. This means that the test will give a false negative result more often. This is especially likely if virus levels are low, such as very early after the onset of symptoms. Self-tests that you can buy in shops are antigen tests. Always follow the manufacturer’s instructions carefully when using a self-test.
Serological test or antibody test
The serological test determines if there are specific antibodies against the SARS-CoV-2 virus in your blood. Antibodies are part of your natural defences (the immune system) and indicate that you have built up protection against the infection. The antibody response is how your body responds to the antigens that are on the virus, and are therefore found after antigens are present. It can take 2 to 3 weeks for your body to produce the right antibodies and release them in sufficient quantities in your blood, so they can be detected. The test shows if you have had the virus in the past, and cannot be used to show if you are infected right now. When you are vaccinated, your body also makes antibodies, so the serological test will also show a positive result after vaccination. This test is primarily used by doctors who are treating specific patient groups, or for research and screening at the population level, by selected laboratories.
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