REGULAR QUESTIONS AND ANSWERS
An Antibody test is to detect the molecules (i.e. antibodies) that people produce after being infected with the virus. Antibodies may take several days to produce after infection and usually remain in the blood for a period after the patient recovers. There are two types, IgM Antibodies which are produced initially to fight the infection, but which disappear after several weeks, and IgG Antibodies which are produced later in the cycle and which generally remain in the body much longer. Therefore, whilst the antibody test has very limited use in the diagnosis of a new COVID-19 infection, it is essential to indicate potential immunity. However, at present, it unknown how long such immunity may subsist.
An Antigen test is based on an immune reaction, whilst the nucleic acid test is based on genetic information. Therefore, an Antigen test can be much faster than the nucleic acid test (15 minutes compared with 4 hours).The cost of speed is the sensitivity. That is, an Antigen test is not as sensitive as a nucleic acid test. The nucleic acid test can detect a microscopic amount of SARS-CoV-2 virus due to its sensitivity using the amplification process of virus genetic information. This is why a PCR test takes several hours and is capable of causing aerosol contamination.
As an Antigen test detects the virus itself sample collection is very important because the virus is only present in some areas of the body. This is different from the collection of a blood sample for an Antibody test when we may expect the Antibodies to be present throughout the patient’s venous blood, although likely to be less present in capillary blood. Accordingly, we recommend the use of a sputum sample, because sputum is a secretion from the respiratory tract where the SARS-CoV-2 virus clusters the most.Hence using sputum provides a more certain method of successfully collecting a reasonable quantity of the virus in the sample, if it is present when compared with the back of the throat nasopharyngeal sample. Because the virus is unevenly distributed on the nasopharyngeal mucosa, it is not certain that a successful sample will be obtained from this area which may lead to a false-negative result. It is much more difficult and requires both expertise and some luck to obtain a truly representative sample from the back of the throat. Therefore, the nasopharyngeal sample accuracy will be lower than that of sputum. Studies have shown that after people are infected, the viruses survive, and thus can be detected, in the digestive tract, especially in the intestinal stool. Therefore, if convenient (e.g. in the hospital or at home), a stool sample is another option for testing; Saliva samples mixed with sputum also have a certain probability of detection, although the amount of virus contained is lower than pure sputum.
Sputum is the mucus that is coughed up from the lower airways (the trachea and bronchi). When taking a sample one should avoid its contamination / dilution with saliva so far as possible. Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth.
The WHO has always been a supporter of Antigen testing. Experts point out that compared with conducting an accurate test every two weeks, conducting a relatively insensitive quick test twice a week can more effectively contain the spread of SARS-CoV-2. The reason is that it is more helpful in containing the spread of the infection where the focus is on identifying those who are likely to spread SARS-CoV-2, rather than locating anyone who is infected in any way with SARS-CoV-2 – but with a low infection much less likely to spread it.
The first EASY-TO-USE COVID-19 tests are now CE certified and approved for distribution and sales across all Europe.