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What are 'one target positive' results for nucleic acid tests?

Updated: Nov 3, 2021 chinadaily.com.cn Print
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It is possible for some people to obtain "one target positive" results after taking the nucleic acid test. Diagnostic tests for the novel coronavirus have been developed to target mainly at least two distinctive viral genes. In some instances, only one of the targets is detected and it does not warrant a confirmed case. This can be interpreted any of three ways.

First, it may be a false positive that requires further testing. The potential causes range from reagent qualities, test kit malfunctions, to accidents during sample transport and other human errors. In addition, NCT is often conducted in batches and in enormous quantities, leading to the occurrences of unclear and inconclusive results. Even for the most precise of diagnostic tools, it is impossible to be 100 percent accurate.

Second, the novel coronavirus is a tiny organism on a nanometer scale. It is impossible to directly observe a single virus in a sample. The principle of NCT is to copy thousands of viral nucleic acids, and use fluorescent substances to track the two distinctive genes during the process. If both genes are found during repeated replication, it is a positive result.

Thus, a person may not have been infected, but may have been exposed to environments that contained fragments of the virus. After a virus split or becomes inactivated, a person stained with fragments of the virus may exhibit only one distinctive gene during testing, which indicates the risk of an infection, but it cannot be diagnosed until further testing.

Third, if the virus has undergone major mutation, one of its distinctive genes used as reference for diagnosis may have become different from the original. Current NCT reagents can only detect the genes that have not mutated, leading to "one target positive" results.

Viral mutations are often causes for concerns and vigilance. However, the probability of the third case is very low because scientists have considered the possibility of mutation when designing NCT reagents, and selected distinctive genes in relatively stable regions of the virus as diagnostic references.

One target positive NCT result does not confirm novel coronavirus infection in a person. Subsequent follow-up tests will be conducted while taking into account epidemiological history, clinical symptoms, antibody testing, and imaging results.

At the same time, it is important for the general public to stay calm, follow personal protection guidelines, cooperate with emergency response mechanisms, and assist medical workers in contact tracing should a virus infection be confirmed.

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