I’m a doctor and this is how WATER or fizzy drinks can give a false positive lateral flow

LATERAL flow tests are a great way to keep people safe from Covid, and if you test positive then you must isolate in order to stop the spread of the bug.

Everyone worries about getting a false positive on a test – and one doctor has revealed how what you drink could make a difference.

When taking a lateral flow test (LFT) you should read the instructions on the box as each one is different and some are made by different manufacturers.

One of the main instructions on most packs though is that you should wait 30 minutes after eating or drinking to take the test.

This is due to the fact that some foods and drinks, such as water and fizzy pop, can interfere with the test.

Posting to TikTok, Dr Karan Rajan explained why these popular beverages could create a false positive.

The NHS doctor said: "First we need to look inside the lateral flow device.”

He adds: “This grey box and the portion just above it contain antibodies that are sensitive to the Covid-19 virus.

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"If you use things like soda, tap water and fizzy drinks, that's going to provide an altered pH, which will affect the function of the antibodies on the test line.

“That is why you need to use this buffer solution (consisting of 99.7 percent saline solution) which provides a stable pH that will actually make the test work."

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Lateral flow tests are an easy way to detect Covid fast and it was this week announced that some people testing positive with Covid will no longer need to take a follow up PCR test due to how wide spread the virus now is.

While cases are wide spread across the country, most people catching Omicron say there are experiencing symptoms similar to a common cold.

A string of hugely positive studies show Omicron is milder than other strains, with the first official UK report revealing the risk of hospitalisation is 50 to 70 per cent lower than with Delta.

Covid booster jabs protect against Omicron and offer the best chance to get through the pandemic, health officials have repeatedly said.

The Sun's Jabs Army campaign is helping get the vital extra vaccines in Brits' arms to ward off the need for any new restrictions.


As well as jabs, regular testing has become a way of life for Brits.

Experts have previously also explained why a faint line could also be a false positive.

Posting a photo of a vaguely positive lateral flow to Instagram, London-based A&E doctor Nathan explained what it could mean.

He said: “Essentially, if *any* line appears before the end of the interpretation window (check leaflet, usually this is 30 minutes), then this is a *positive* test and you must isolate and book a PCR. 

“However, if a line appears *after* the interpretation window then this does NOT count as a positive test. You do not need to isolate and you do not need to book a PCR.”

But if you have symptoms, regardless of the lateral flow test result, you should isolate and book a PCR test.

The full list of reasons to get a PCR test

In England, the reasons for ordering a PCR test are:

  1. You have Covid symptoms 
  2. You’ve been in contact with someone who’s tested positive and you must self-isolate
  3. You’ve been asked to get a test by a local council or someone from NHS Test and Trace
  4. A GP or other health professional has asked you to get a test
  5. You’re taking part in a government pilot project
  6. You’ve been asked to get a test to confirm a positive result
  7. You’ve received an unclear result and were told to get a second test
  8. You need to get a test for someone you live with who has symptoms (you can order tests for up to three household members) 
  9. You’re in the National Tactical Response Group
  10. You are due to have surgery or a procedure (in some occasions)

Exceptions to the lateral flow test rule:

  1. People who are eligible for the £500 Test and Trace Support Payment (TTSP) will still be asked to take a confirmatory PCR so they can access financial support
  2. People participating in research or surveillance programmes may still be asked to take a follow-up PCR test
  3. Around one million people in England who are at particular risk of becoming seriously ill from Covid are involved in new research of treatments

Rules may vary between nations, for example in Scotland, you should book a PCR test if you have had two or more void lateral flow test results.

And in Wales, those who are in a “clinically vulnerable” group will still need to take a PCR test if their lateral flow is positive but they have no symptoms.

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