With the Omicron wave showing no signs of slowing, COVID-19 cases are surging and it feels like every second person has either contracted or been a close contact to the virus. Rules keep changing, PCR test wait times are impossible and accessing a rapid antigen test (RAT) right now feels something like winning a golden ticket to the Willy Wonka factory.
At this point though, most of us have had to take at least one RAT (when we can get our hands on them). While understanding how to read these results is fairly simple, one thing is less broadly understood: what do ‘C’ and ‘T’, the letters that reveal your results, actually stand for?
Covid and Totally Fine? Clear and Tough Luck? The meaning behind these two letters is not something that comes clearly labelled on the packet, so if you’ve ever found yourself wondering what ‘C’ and ‘T’ stand for, we’re here to help.
What do the ‘C’ and ‘T’ stand for on a rapid antigen test (RAT)?
To answer this question we consulted with one of the most reliable resources in the world of COVID-19, the WHO. On the WHO website, the health body has shared a breakdown of how to use RATs and what all the pieces involved mean.
Under the section ‘Interpreting Results’ it states that ‘C’ (which indicates a negative result) stands for Control Line and ‘T’ (which indicates an inconclusive result) stands for Test Line.
If your test shows a line across both C and T, you have a positive result.
The explainer reads as follows:
1. A colored (sic) band will appear in the top section of the result window to show that the test is working properly. This band is control line (C).
2. A colored (sic) band will appear in the lower section of the result window. This band is test line of SARS-CoV-2 antigen (T).
3. Even if the control line is faint, or the test line isn’t uniform, the test should be considered to be performed properly and the test result should be interpreted as a positive result.
The WHO also briefly explains the relevance of the control and test line in this document, sharing that “the control line is used for procedural control, and should always appear if the test procedure is performed properly and the test reagents of the control line are working”.
On the other hand, a coloured test line will only appear “if SARS-CoV-2 antigens are present in the specimen”. Interestingly, it is also highlighted here that the intensity of the appearance of the test line “will vary depending upon the amount of SARS-CoV-2 antigen present in the specimen”.
In saying that, even the faintest test line should be treated as a positive result.