Antigen – antibody test kit

An antigen – antibody test kit is a medical testing tool used to detect the presence of specific antigens or antibodies.

I. Basic Principles

1. Antigen – Antibody Reaction
   • It is based on the specific binding reaction between antigens and antibodies. When antigens (usually specific molecular structures of foreign pathogens or abnormal substances in the body) enter the body, the immune system will produce corresponding antibodies to identify and bind to these antigens.
   • In the test kit, this specific binding is used as the basis for detection. For example, if the target antigen exists in the sample, when the sample is added to the test kit, the specific antibody against the antigen pre – coated in the test kit will bind to it, forming an antigen – antibody complex.
2. Labeling Techniques
   • In order to make the test results visible, the test kit usually adopts labeling techniques. Common labels include enzymes, fluorescent substances, radioactive isotopes, and colloidal gold.
   • Taking colloidal gold labeling as an example, after the antigen – antibody binding occurs, the antibody or antigen labeled with colloidal gold will accumulate in the detection area, resulting in a visible color change. If the target antigen or antibody does not exist in the sample, this color change will not occur, or the color change will appear in the control area, indicating a negative test result.

II. Composition and Structure

1. Sample Collection Devices
   • They include swabs (such as swabs for collecting samples from the nasal cavity, throat, etc.) or blood – drawing needles and blood collection tubes (when collecting blood samples), which are used to obtain samples to be tested.
   • Some of these collection devices are designed to be convenient for patients to collect samples by themselves, improving the convenience of testing. For example, in some COVID – 19 antigen test kits, the nasal swabs are simple in design, and patients can collect nasal secretions by themselves under guidance.
2. Reaction Membranes or Test Strips
   • This is one of the core components of the test kit, on which specific antibodies or antigens are usually coated.
   • When the sample is added, the antigen – antibody reaction occurs on the reaction membrane. The reaction membrane generally has different areas, such as the test area (T – area) and the control area (C – area). The reaction occurring in the test area can determine whether the target substance exists in the sample, and the control area is used to verify whether the testing process is valid.
3. Reagents
   • They include buffers and other reagents, which are used to process the sample to make it suitable for reaction in the test kit.
   • Buffers can adjust the pH value of the sample and prevent other components in the sample from interfering with the antigen – antibody reaction. For example, the buffer in some test kits can lyse the virus, release the antigen, and maintain the activity of the antigen so that it can bind normally with the antibody.
4. Housings and Auxiliary Components
   • The test kit has a housing to protect the internal test strips and reagents from contamination and damage.
   • It may also include some auxiliary components, such as droppers (used for accurately dropping samples and reagents) and instruction manuals (guiding users on how to correctly perform test operations).

III. Main Applications

1. Disease Diagnosis
   • It is widely used in the diagnosis of infectious diseases. For example, in the diagnosis of influenza virus infection, by detecting the influenza virus antigen in the patient’s sample, it can quickly determine whether the patient is infected with the influenza virus. This rapid diagnosis helps doctors formulate treatment plans and take isolation and other prevention and control measures in a timely manner.
   • For some sexually transmitted diseases, such as syphilis and AIDS, the corresponding antigens or antibodies can also be detected to assist in diagnosis. In AIDS testing, by detecting the AIDS virus antibodies in the blood, it can be judged whether an individual is infected with the AIDS virus, which is of great significance for the early detection and intervention of AIDS.
2. Epidemic Monitoring and Prevention and Control
   • During the outbreak and epidemic of infectious diseases, antigen – antibody test kits play an important role. Taking the COVID – 19 pandemic as an example, the COVID – 19 antigen test kits can screen a large number of people in a short time and quickly identify possible infected individuals.
   • This rapid screening helps to timely discover the spread of the epidemic and plays a key role in controlling the spread of the epidemic. Compared with nucleic acid testing, although antigen testing is less sensitive, it has the advantages of being fast, simple, and self – operable, and is suitable for large – scale preliminary screening.
3. Immune Status Evaluation
   • It can be used to evaluate an individual’s immune status. For example, after vaccination, by detecting whether antibodies against the disease prevented by the vaccine are produced in the body, it can be judged whether the vaccine has produced an immune response in the individual.
   • For some autoimmune diseases, by detecting the levels of autoantibodies in patients, it can assist doctors in understanding the progress of the disease and the treatment effect. For example, in the diagnosis and treatment of systemic lupus erythematosus, detecting the levels of antinuclear antibodies and other autoantibodies helps doctors adjust the treatment plan.