A rapid antigen test detects proteins from SARS-CoV-2, the virus that causes COVID-19, in a sample. You can collect the sample yourself at home using a nasal swab or saliva.

Here’s how to make the most of these rapid antigen tests, and to increase your chance of a meaningful result.

These tips come from analysing instructions on the TGA website about how to use approved rapid antigen tests. Here’s what to consider:

1. Check the expiry date. Don’t use a test that has expired
2. Some tests need to be at room temperature for 30 minutes before use. So plan ahead
3. If you are using a nasal swab, blow your nose before collecting the sample. If using a saliva test, don’t eat or drink 10 minutes before collecting the sample
4. Avoid contaminating the sample. Regardless of which test you use, instructions can ask you to clean a flat surface; wash or sanitise and dry your hands; and lay out the test items. Never, ever touch the business end of the swab (the soft end that goes in your nose) as you will contaminate it
5. Follow the instructions on sample collection to the letter. For example, with a nasal swab you will be asked to insert the swab 2cm, rotate the swab five times, and do this in both nostrils. Once you have collected the sample it goes into the chemical solution
6. Place a set number of drops of the solution on the indicator device. Don’t add extra “for good luck”
7. Read the results at the exact time recommended. For example, the instructions may ask you to read the result no earlier than 15 minutes after adding the solution and no later than 20 minutes. After 20 minutes the result may no longer be accurate.

What do the coloured lines mean?

There are two coloured lines to look for. One is a C (the control). This tells you if the test is working properly. The other is a T (test) or Ag (antigen). And it’s the combination of these that gives the result:

• if the C coloured line fails to show, the test is invalid. The test kit may have expired, or you didn’t take the test correctly
• if the C coloured line shows and the T (or Ag) line does not, your result is negative (you’re unlikely to have COVID-19)
• if both the C and T (or Ag) lines show up, your result is positive (you’re likely to have COVID-19).

What next?

If you get a negative result and don’t have symptoms, congratulations! If you have a negative result but have symptoms, take a PCR test to be sure. Avoid contact with others in the meantime.

If you get a positive result, follow up as soon as possible with a PCR test to confirm and self-isolate in the meantime.

This was originally published in The Conversation, 22 November 2021.