Difference between antibodies to salivary antigens and antibodies to swab antigens

1. Saliva Antigen – Antibody Test

1. Principle
   • It is based on the principle of specific binding of antigens and antibodies. When a person is infected with certain pathogens, the antigens of the pathogens may appear in saliva. The saliva antigen – antibody test kit contains specific antibodies against specific pathogen antigens. When a saliva sample comes into contact with the reagents in the test kit, if the corresponding antigen exists in the saliva, an antigen – antibody binding reaction will occur.
   • Labeling techniques are usually used to display the reaction results. For example, using antibodies labeled with colloidal gold, after antigen – antibody binding, the aggregation of colloidal gold particles will produce a color change, and the results are judged by observing the color changes in the test area and the control area.
2. Operation Procedure
   • Sample Collection: The examinee needs to spit saliva into a clean collection container. The collection volume is generally carried out according to the requirements of the test kit, usually about several milliliters. During the collection process, attention should be paid to avoiding mixing in food residues, blood and other impurities to avoid affecting the test results.
   • Sample Processing (if necessary): Some test kits may require simple processing of the saliva sample, such as adding a diluent, etc., to ensure that the sample can react normally in the test kit.
   • Testing Operation: Drop the processed saliva sample onto the specified area of the test kit and wait for a certain period of time (usually ranging from a few minutes to a dozen minutes) and observe the color changes in the test area and the control area.
   • Result Interpretation: If the specified color changes occur in both the test area and the control area, it usually indicates a positive result, that is, the target antigen exists in the saliva; if only the control area shows a color change, it is a negative result; if there is no color change in the control area, the test may be invalid.
3. Advantages
   • Non – invasive and Convenient for Collection: Compared with blood collection, saliva collection does not require needle – sticking and is non – invasive to the examinee, and is more easily accepted, especially for children and people who are afraid of blood. The examinee can collect the saliva sample by himself, and the operation is relatively simple.
   • Quick Results: Generally, test results can be obtained within a relatively short period of time (such as about 15 minutes), which is suitable for on – site rapid testing and preliminary screening.
4. Limitations
   • Relatively Low Detection Sensitivity: The antigen concentration in saliva may be lower than that in blood, and the composition of saliva is relatively complex. There may be some interfering substances, resulting in lower detection sensitivity than blood tests, and false – negative results are likely to occur.
   • Limited Scope of Application: Not all pathogens can be detected through saliva. Currently, it is mainly used for the detection of some specific pathogens, such as some respiratory viruses.

2. Swab Antigen – Antibody Test

1. Principle
   • It is also based on the specific binding of antigens and antibodies. The swab is used to collect mucosal samples from specific parts (such as the nasal cavity, throat, etc.). After the pathogen infects these parts, the pathogen is likely to accumulate here. The sample collected by the swab comes into contact with specific antibodies in the test kit, and if the target antigen is in the sample, a binding reaction will occur.
   • Similar labeling techniques are used to display the results, such as colloidal gold labeling. When antigen – antibody binding occurs, the presence of the target antigen is judged by color change.
2. Operation Procedure
   • Sample Collection:
     • Nasal Swab: Gently insert the swab into the nasal cavity and rotate it several times along the nasal cavity wall to ensure sufficient collection of nasal mucosal samples. Generally, the collection time for each side of the nasal cavity is about 15 – 30 seconds.
     • Throat Swab: Ask the examinee to open his mouth wide, and use the swab to wipe the bilateral tonsils and the posterior pharyngeal wall, also rotating it several times for collection.
   • Sample Processing (if necessary): After some swab samples are collected, they may need to be placed in a tube containing a preservation solution or a treatment solution for soaking or processing for a certain period of time, so that the antigens in the sample are fully released or stabilized.
   • Testing Operation: Drop the processed swab sample or a certain amount of liquid sucked from the treatment solution onto the corresponding area of the test kit, and observe the color change after waiting for the specified time.
   • Result Interpretation: Similar to the saliva antigen – antibody test, positive, negative or invalid test results are judged according to the color changes in the test area and the control area.
3. Advantages
   • Strong Targeting: For pathogens that reproduce in parts such as the respiratory mucosa, swab collection can directly obtain samples from the parts where the pathogens may exist, which is relatively more targeted, and the detection accuracy may be higher in some cases.
   • Wide Scope of Application: It can be used for the detection of pathogens infecting various parts such as the respiratory tract and digestive tract. For example, during the COVID – 19 pandemic, nasal swab and throat swab antigen tests were widely used.
4. Limitations
   • The Collection Process May Cause Discomfort: Whether it is a nasal swab or a throat swab, the collection process may cause some discomfort to the examinee, such as nasal irritation and nausea reflex in the throat, especially for children and some sensitive people.
   • Relatively High Operational Requirements: If the swab collection operation is not standardized, such as inaccurate collection parts and improper collection force, it may lead to poor – quality samples and thus affect the test results.