COVID-19: Home testing kits may give false negative results, medical expert says

As several people are opting for self-test COVID kits amid a surge in infections in India, it has been learnt that there is a chance for false-negative reports in-home testing kits even after an individual shows coronavirus infection symptoms. Therefore, medical experts have advised people with COVID symptoms to self-isolate to prevent the infection from spreading further. 

Dr Harsh Mahajan, Founder and Chief Radiologist, Mahajan imaging, told ANI, "There are two kinds of tests that are being done. One is the home tests, which are the rapid antigen tests and these have quite a limited sensitivity. These are about 50% as sensitive as the gold standard RT-PCR test, so you may get a false negative test on these testing kits."

Dr Harsh mentioned that many cases have been reported where the test shows negative despite people showing COVID symptoms. 

RT-PCR v/s Home testing kits

Explaining why there is a chance of false-negative reports concerning self-test, Dr Harsh Mahajan said, "In these home test kits, there are chances of not taking proper sampling from the back of nose or throat. As a result, a 'positive' report might not come."

Providing details on the accuracy of RT-PCR tests, the radiologist mentioned that there is only a 10% chance of false-negative reports in RT-PCR tests as they are conducted in the lab. He added that if the RT-PCR test is conducted properly then by and large the report comes positive if the patient is symptomatic. It was also learned that the report comes negative if the incubation period is long. 

Testing for Delta and Omicron variant

Stating that the incubation period is different for both the COVID variants, Delta and Omicron, Dr Harsh said, "During the Delta variant, the rough average incubation period was about five days. So, we used to tell people not to get tested immediately after the exposure because they would come negative. It does take between two to 14 days of incubation with an average of five days." 

Explaining the Omicron variant's incubation period, Dr Harsh mentioned that the incubation period is lesser for the Omicron COVID strain which is currently the predominant variant. According to him, people must test for this variant on the third day.

The health expert informed that a patient will test positive for the variant if s/he has symptoms, and hence, it is ideal to take the test on the first few days if one is experiencing the symptoms. 

(With inputs from ANI, Image: PTI)