Covid-19 antigen tests in the age of omicron: Understanding reliability, results and false negatives
In Spain, a person infected with Covid has to self-isolate for seven days after the onset of symptoms, and seven days after a positive result for asymptomatic cases.
Covid-19 tests that use lateral flow technology to quickly check for the presence of antigens (proteins on the outer shell of the SARS‑CoV‑2 virus) have become the primary way to detect infections in the era of the omicron variant. In Spain, where the healthcare system is feeling the strain of the sixth coronavirus wave, authorities now recommend performing rapid tests and self-isolating in the event of a positive result.
Rapid antigen tests are not as accurate as PCRs, which are handled in a lab, but they have several advantages: they are faster, cheaper, can be done at home and have proven sufficiently sensitive when the person has a higher viral load and is therefore more contagious (although the spread of the omicron variant is complicating this picture).
The tests can produce two lines once the sample is collected and added by droplets to the kit. The first line is marked (C) for control and the second is (T) for test. The C line simply indicates the test has been completed correctly, while the appearance of a T line indicates that a viral load has been detected in the sample. However faded or clear this second line, if it shows up the result is positive.
