Antigen test unreliable in asymptomatic patients

Lab technician holding swab collection kit,Coronavirus COVID-19 specimen collecting equipment,DNA nasal and oral swabbing for PCR polymerase chain reaction laboratory testing procedure and shipping
A study carried out in Elche shows that the coronavirus antigen test is unreliable in asymptomatic patients. The study also claims that the test delivers a high percentage of false negatives, especially in patients who do not have symptoms or who have had symptoms for more than six days.
The study was carried out with samples from more than a thousand patients who came to local health centres and those who were tested by the emergency services, suspected of having covid-19.
“It is one of the most extensive studies that has been done, both in terms of the number of patients and the variety, since it has been applied to children and adult populations, as well as in different settings”, explained Félix Gutiérrez, head of Internal Medicine of the General Hospital of Elche. With the samples of these patients, antigen and PCR tests were performed simultaneously, and the results were compared.
“We found that there were very few false positives and where the antigen test works especially well is when it comes to detecting patients with symptoms of less than six days of evolution,” said Mar Masia, head of the Infectious Diseases unit of the Elche hospital. From the sixth day of symptoms, the accuracy of the antigen test is lower.
The study also found significant differences based on the age of the patients. In patients between 0 and 14 years of age, the antigen tests yielded a higher percentage of false negatives. The researchers’ hypothesis is simply “that, as the test is very annoying, the children withdraw immediately, which makes it difficult to take the sample,” explained Félix Gutiérrez.
Following the study, the researchers concluded that antigen testing would not be a valid test to apply to mass screening programmes. In terms of the results obtained for children and young people, Mar Masia insists on the need for schools to perform PCR tests on those children who have symptoms of the disease when the antigen test has come back negative.