A common perception regarding all diagnostic tests is that they can’t always be black or white; even for the COVID-19 test, there are high chances that it is either negative or positive. Naturally, everyone wants to be tested negative but sometimes the COVID-19 test comes back as ‘weak positive’. What is a weak positive test? Does this mean you are infected with the coronavirus or not infected?
The standard test for identifying coronavirus (SARS-CoV-2) in the body is a Polymerase chain reaction (PCR) test. Although, the cases of coronavirus reported in official records are either positive or negative recently a new case is highlighted which is reported as a ‘weak positive COVID-19 case”.
This PCR testing is not just limited to coronavirus but also helps to identify a number of other pathogens. They identify the genetic material of the virus in the sample and if it is present, it reports positive.
But for this identification process, the final result is based on how many times the genetic material is identified in the sample. Following a threshold as standard, it is either called a positive or negative result.
We identify a sample to be positive or negative based on the number of times we need to amplify the small segments of genetic material to detect the virus—and whether this number falls below or above a certain threshold.
When a person is severely infected, he is much likely to have lots of genetic materials identifiable from his sample. These genetic materials show up in each round of PCR and based on this result, the sample is marked positive.
On the other side, if the viral genetic material is lower than the standard, the sample is marked negative. But in case of a weak positive COVID-19 test report, the viral load varies above or below the threshold level. It is necessary to understand that these thresholds don’t present 100% accuracy and it is also possible for this test to be a false negative or a false positive.
A person who is given a weak positive COVID-19 test report could mean that the viral particles are detectable but not virulent. This situation makes it hard to understand if the virus will cause disease or not.
He was tested negative but a then a small amount of viral particles were identified in his blood, making his COVID-19 test, a weak negative. Health experts believe these types of tests are more likely in those who have weak immunity.
The weak positive COVID-19 test is typically considered a presumptive positive test where it is presumed to be positive unless there is information to change this information. The diagnostic guidelines recommend re-testing a person with a weak positive report by running the sample on PCR again.
Mostly, running the same samples for more tests gives a better picture of the situation but sometimes a new sample obtained and tested is more desirable. In this second testing, a different genetic region of the virus is picked for identifying its presence in the sample. These types of reference tests confirm the virulence of the pathogen in a person.