Doctors warn that over-the-counter carrageenan-based nasal sprays affect accuracy of PCR tests for detecting SARS-CoV-2
Nikhil Prasad Fact checked by:Thailand Medical News Team Feb 09, 2025 1 month, 4 days, 12 hours, 24 minutes ago
Medical News: Common Nasal Sprays May Interfere with COVID 19 PCR Tests
A new study has raised concerns over the potential impact of over-the-counter carrageenan-based nasal sprays on the accuracy of PCR tests used to detect COVID-19. The research, conducted by Australian scientists and doctors from Northern Clinical Diagnostics and Thrombovascular Research Centre at Northern Health, Melbourne, in collaboration with Monash University, University of Melbourne, Murdoch Children’s Research Institute, and Royal Children’s Hospital, found that certain nasal sprays could cause invalid or inaccurate results in COVID-19 testing.
Doctors warn that over-the-counter carrageenan-based nasal sprays affect accuracy of PCR tests for detecting SARS-CoV-2
Carrageenan, a substance derived from red seaweed, is commonly used in nasal sprays marketed for their antiviral properties. Given that carrageenan is structurally similar to heparin, a compound known to interfere with PCR testing, the researchers aimed to assess whether carrageenan could have a similar effect. This
Medical News report explores the study’s key findings and their implications for public health.
How Carrageenan Affects PCR Test Results
The researchers tested four different diagnostic platforms used for detecting SARS-CoV-2 and found that while some platforms remained unaffected, others produced inaccurate or invalid results when samples were exposed to carrageenan. Notably, PCR tests conducted using the Seegene STARlet platform were significantly impacted, returning up to 80% invalid results when carrageenan was present.
To confirm the findings, the team tested both commercial nasal sprays containing carrageenan and a research-grade formulation of iota-carrageenan. The results consistently showed that carrageenan interfered with PCR testing, potentially leading to false negative results. This interference was observed across multiple brands of nasal sprays, demonstrating that the effect was not limited to a specific formulation but was a broader issue with carrageenan-containing products.
Impact on COVID 19 Testing and Public Health
The study also conducted in vivo experiments, where a volunteer used a carrageenan-based nasal spray and then underwent PCR testing at various time intervals. Within 15 minutes of nasal spray usage, test results showed increased cycle threshold (Ct) values, indicating potential interference. However, by 60 minutes post-application, the Ct values returned to normal, suggesting that the interference may be temporary.
Despite this, the researchers warned that individuals using carrageenan nasal sprays shortly before undergoing PCR testing may receive inaccurate results. A false negative result could lead to an infected individual unknowingly spreading the virus to others, raising significant concerns about the impact of these nasal sprays on pandemic management and other respiratory disease monitoring.
Comparing Carrageenan to Heparin Int
erference
A further comparison between carrageenan and heparin showed that while heparin had a more severe impact on PCR testing, carrageenan interference was still considerable. Importantly, the researchers found that carrageenan interference could not be reversed using heparinase I, an enzyme known to counteract the effects of heparin on PCR tests. This finding suggests that there is currently no straightforward way to mitigate the impact of carrageenan interference on PCR-based diagnostics.
Study Recommendations and Future Research
The researchers recommend that individuals refrain from using carrageenan-based nasal sprays for at least one hour before undergoing PCR testing to minimize the risk of inaccurate results. They also suggest that medical professionals take into account nasal spray usage when interpreting PCR test results.
Additionally, the findings highlight the need for further research into how carrageenan interacts with PCR testing mechanisms. The study underscores the importance of evaluating the potential effects of commonly used over-the-counter medical products on diagnostic accuracy, particularly in the context of infectious disease testing.
Conclusion
This study provides compelling evidence that carrageenan-based nasal sprays can interfere with PCR testing for SARS-CoV-2, potentially leading to invalid or false negative results. Given the widespread availability and use of these sprays, their impact on COVID-19 testing accuracy could have significant public health implications. The researchers emphasize the importance of being aware of this potential interference and recommend that individuals avoid using these sprays shortly before undergoing PCR testing. More research is needed to fully understand the mechanisms behind this interference and to explore possible solutions to mitigate its effects in diagnostic settings.
The study findings were published in the peer-reviewed journal: PLOS ONE.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0316700
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https://www.thailandmedical.news/articles/coronavirus
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