You have been exposed to COVID and are starting to get symptoms. But after a few days of testing with rapid antigen tests (RATs), your tests remain negative.
Bulk PCR testing has been scaled back, so in what situations can you get a PCR? And why could it be useful?
RATs are less sensitive to current variants
PCR tests are more sensitive than RATs. They recognize viral RNA and do not require high concentrations of virus, meaning diseases can be detected early. PCRs are accurate about 95% of the time.
In contrast, a RAT can only detect the viral proteins present in the sample. So it’s less sensitive and requires more virus, which is likely to accumulate later in the disease process, before giving a positive result.
RATs accurately detected approximately 81% of positive cases in earlier variants like Delta. However, estimates for Omicron are lower and not consistent across studies, varying on average from about 55% (without symptoms) to 73% (with symptoms). Results will vary depending on the stage of infection, degree of symptoms, and the individual kit used, among other things.
We are still awaiting the Therapeutic Goods Administration’s independent review of the RAT kits for the new Omicron subvariants, however the limited evidence suggests that RATs may be less effective against these new variants.
The United States Food and Drug Administration recently recommended repeat testing on consecutive days to reduce the risk of missing an infection (known as false negatives).
An infected person will test positive on a PCR test one to two days before an RAT. It may take a few days after symptoms appear for the RAT to become positive.
Why were PCR test sites closed?
Across Australia, the number of PCR testing facilities has been significantly reduced since mid-year.
One reason is that PCR testing is an expensive government service (each test costs around A$70) and running the testing centers requires staff to be redeployed from other roles. This requires large amounts of refilling and rearranging.
Today, RATs are generally the preferred testing approach by health authorities.
So who is a candidate for a PCR?
Below are the current guidelines for using RATs versus PCR for each state – and the advice on what to do if you test positive or have COVID symptoms. Click the gray plus sign (+) in your state or territory to learn more.
In some states, PCRs are prioritized for people at higher risk of serious illness.
If your RATs continue to be negative and you have symptoms, you can request a PCR from your GP.
However, according to the National Coronavirus Hotline, you will generally receive a PCR if you visit a testing site that is still operational and specifically asks for a PCR.
You can use this tool to find exam centers that are still active.
Why is an accurate COVID test important?
Knowing that you are COVID positive is important for many reasons. It allows you to isolate and avoid spreading disease to loved ones and those most at risk. You can also notify close contacts.
If you become very ill, you may be considered for COVID medication and your healthcare providers can monitor the long-term effects of COVID such as blood clots, neurological side effects, and other long-term complications.
They could also be eligible for antiviral COVID treatments aimed at preventing those at higher risk of serious illness from contracting COVID. These are only available by prescription from a doctor and are most effective if started within five days of your symptoms appearing.
Getting an accurate result is especially important if you live, work, or are in high-risk environments such as:
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Citation: My RATs are negative but I still believe I may have COVID. Should I have a PCR test done? (2022, November 25) Retrieved November 25, 2022 from https://medicalxpress.com/news/2022-11-rats-negative-covid-pcr.html
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