The difference between influenza A/B antigen test and nucleic acid test

Influenza, commonly known as “the flu,” is an acute respiratory infection caused by the influenza virus, which is highly contagious and spreads mainly through coughing and sneezing.

The influenza virus is classified into three types: A, B, and C. Type A influenza virus has strong mutability, type B is less so, and type C is very stable. Therefore, type A influenza virus is more widespread and severe than type B.

The winter and spring seasons are the peak seasons for infectious diseases, and with the start of the new school year, there has been a recent surge in cases of type A influenza. According to incomplete statistics, the positive rate of influenza virus antigen detection in the emergency department of a hospital was 21% in February and has recently reached 27%. Many patients have undergone both influenza virus antigen and nucleic acid testing, and feedback has indicated that the results are inconsistent. So, how should we interpret these two test results?

Method Differences

Methods for detecting influenza virus mainly include virus isolation and culture, antigen detection, and nucleic acid testing. Virus isolation and culture, as the traditional gold standard, are indispensable methods for studying virus antigenicity, genetic variation characteristics, and vaccine preparation. However, due to the complexity of the operation and the long detection time, it is difficult to use in clinical settings. Currently, the most commonly used methods are rapid antigen detection and nucleic acid testing, and the advantages and disadvantages of each method can be seen in Table 1.

Differences Between Influenza Antigen Test and Nucleic Acid Test

Nucleic Acid Test

Nucleic acid testing technology targets virus-specific DNA or RNA sequences and can detect viruses earlier in clinical samples. This method has higher sensitivity and specificity compared to antigen detection, can differentiate between different subtypes of influenza viruses, and simultaneously detect multiple viruses. However, its disadvantage is high cost, complex equipment, requires professional personnel to operate, and typically takes 1-8 hours to complete.

Standard collection and handling of Sampling

Hospitals usually only conduct antigen rapid tests, and nucleic acid tests are usually conducted by local disease control centers. If a patient’s nucleic acid test result is inconsistent with the antigen result, it may be due to factors such as sample collection, storage, and processing that cause false negatives or false positives. It does not mean that the quality of the laboratory testing is problematic, but further confirmation or the use of other methods is needed.

Why might there be false negatives in antigen tests? This is mainly due to methodological limitations of antigen detection reagents, which generally have lower sensitivity than nucleic acid detection reagents. Therefore, for negative results that are in doubt, it is recommended to use nucleic acid detection or virus culture identification methods for confirmation.

Other reasons may include:

1. Improper sample collection, storage, unfresh samples, or repeated freeze-thaw cycles
2. Low virus titers in the sample, which should be detected using nucleic acid tests to increase the detection sensitivity
3. Genetic mutations of the virus may lead to changes in antigen determinants, resulting in false negative results
4. The presence of individual drugs in collected samples, such as nasal sprays, can interfere with the results
5. The optimal sampling time after infection (virus titer peak) has not been validated, and collecting samples from the same patient in multiple sessions or from multiple locations can reduce false negatives.

HCY has been dedicated to the field of molecular diagnostics for many years. Even before the outbreak of the COVID-19 pandemic, HCY’s molecular diagnostic products had been widely used in the collection and transportation of samples related to influenza virus, hand-foot-and-mouth disease, rubella and measles, norovirus, rotavirus, and other viruses. These products are mainly used by inspection agencies such as disease control centers, hospitals, and customs for the collection, extraction, and detection of virus samples.

After the outbreak of the COVID-19 pandemic, HCY was one of the first companies with the production capability of virus sampling tubes to be designated as a key enterprise for epidemic prevention and control by the provincial government, following a letter issued by the National Development and Reform Commission. The outstanding performance of its products enabled Huachenyang’s virus sampling products to pass product tests in multiple countries such as North America, Europe, the UK, Australia, and Canada, and became government-designated products in multiple countries such as Canada and Australia.