COVID-19 rapid antigen test

Overview of Treatment

Rapid antigen testing for COVID-19 is a point-of-care diagnostic tool primarily used for quick screening of SARS-CoV-2 infections. This method detects viral antigens in respiratory secretions from patients and can provide results within 15 to 30 minutes, suitable for diagnosing during the acute phase after symptom onset. Compared to PCR nucleic acid testing, rapid antigen tests are easier to operate and more cost-effective, but their sensitivity may be lower, so they should be used in conjunction with clinical judgment.

Types of Tests and Mechanisms

Rapid antigen testing employs lateral flow immunoassay technology, which relies on the specific binding of antibodies to the nucleocapsid (N) protein on the virus surface. The test kit includes a swab, a reaction cassette, and a control line. When sufficient viral antigen is present in the sample, antibody-antigen complexes migrate along the nitrocellulose membrane, producing a color change at the test line indicating a positive result. This mechanism directly reflects viral load, but may produce false negatives in cases with low viral titers.

Indications

This test is mainly suitable for the following scenarios:

• Suspected cases within 5 days of symptom onset
• Self-screening after contact with confirmed cases
• Mass community screening

It is not recommended for screening asymptomatic individuals without exposure history. Cross-validation with PCR testing is advised to improve accuracy.

Usage and Dosage

The testing process involves three steps:

1. Sampling: Use a swab to collect secretions from deep within the nasal cavity (1-2 cm)
2. Reaction: Drop the swab extract into the designated area of the test cassette
3. Interpretation: Observe the color development of the test and control lines within 15 minutes

Strict adherence to the instructions is essential; improper sampling (e.g., insufficient depth) can lead to inaccurate results.

Benefits and Advantages

Main advantages include:

• Short operation time: results within approximately 15 minutes
• Field flexibility: usable in hospitals, communities, or home settings
• Cost-effectiveness: about one-third the cost of PCR per test

Particularly suitable for scenarios requiring rapid decision-making, such as immediate screening in isolation wards.

Risks and Side Effects

The primary risk is false-negative results, which may delay treatment. If symptoms are apparent but the test is negative, PCR confirmation should be performed immediately. Operational errors (e.g., incomplete sampling) may also lead to incorrect results, so testing should be performed by trained healthcare personnel or instructed individuals.

Precautions and Contraindications

Important considerations include:

• Only applicable within 5 days of symptom onset
• Patients with nasal allergies or post-surgical conditions should consult a physician beforehand
• Results after 30 minutes are not valid for diagnosis

Contraindications include recent upper respiratory tract surgery within 2 weeks and young children unable to cooperate with sampling, who should use alternative testing methods.

Interactions with Other Treatments

This test does not have direct interactions with drug treatments but should be used alongside other diagnostic methods. For example:

• Negative results should be confirmed with PCR
• Suspected breakthrough infections are recommended to be evaluated with serological antibody testing

Test results should be integrated with CT imaging, symptom severity, and other clinical indicators for comprehensive assessment.

Effectiveness and Evidence

According to WHO guidelines, the sensitivity of rapid antigen testing within the first day of symptom onset is approximately 70-80%, decreasing to below 50% after the seventh day. Large studies show that when Ct values are below 25, the positivity rate of antigen tests can exceed 90%. Clinical evidence indicates that this method is highly practical for quarantine control and urgent resource allocation in healthcare settings.

Alternatives

Alternative options include:

• RT-PCR nucleic acid testing: high sensitivity but requires laboratory equipment
• Antibody immunoassays: used for tracking immune response post-infection
• Molecular rapid testing devices: such as point-of-care platforms with real-time PCR systems

Selection depends on accuracy requirements, testing environment, and resource availability.

 

Frequently Asked Questions

How can I ensure correct operation steps to improve accuracy when performing COVID-19 rapid antigen testing?

When collecting nasal samples, wash hands thoroughly and adjust the nasal angle according to instructions. Ensure the swab is inserted 1-2 cm into the nasal cavity and remain there for several seconds. Operating in environments below 15°C or incomplete sampling may cause errors. It is recommended to perform testing at room temperature and carefully read the instructions. If the initial result is negative but symptoms persist, retest after 24 hours.

If the rapid antigen test is negative but symptoms like fever and cough remain, what should I do?

Asymptomatic individuals may have insufficient viral load in the early stages, leading to false negatives. If symptoms are consistent with COVID-19 and exposure history is clear, retesting the next day or performing PCR testing for confirmation is advised. If high fever or breathing difficulties occur, seek medical attention immediately and inform the healthcare provider of the test results. The doctor may prescribe treatment based on clinical judgment.

If family members share a rapid test kit, will it affect the accuracy?

The sampling tools within the kit (such as swabs and reagents) should not be shared to prevent cross-contamination or reagent failure. However, the result observation area (e.g., test strip) can be shared. If family members show symptoms, it is recommended that each person uses an individual kit and thoroughly disinfect contact surfaces after testing to prevent residual virus transmission.

When should I seek medical attention immediately after a positive rapid antigen test?

If you experience symptoms such as shortness of breath, oxygen saturation below 95%, altered consciousness, or persistent chest pain, seek emergency medical care. Individuals over 60, those with chronic illnesses, or immunocompromised persons should report to health authorities even with mild symptoms and follow quarantine and treatment guidelines.

What daily protective measures should I continue after a negative rapid test result?

Even with a negative result, if you have been exposed to confirmed cases or are in high-risk environments, continue wearing masks, avoid gatherings, and retest after 3 days. Although vaccination reduces the risk of severe illness, it does not completely prevent infection. Continue practicing hand hygiene and environmental disinfection.