Dr Leen Tannous has busted common myths about what blood tests can and cannot reveal about serious health conditions. TikTok users had a range of responses to her comments
When we’re feeling under the weather and can’t pinpoint why, a blood test is often our first port of call. However, contrary to popular belief, these tests don’t identify every potential major health issue, including the one that people are often most concerned about – cancer.
North West London GP Dr Leen Tannous, who frequently shares health advice on her TikTok account, recently posted a video debunking misconceptions about why doctors conduct blood tests. She stated: “One of the biggest misconceptions I see as a GP is the belief that if something serious – especially cancer – was going on, it would automatically show up on a routine blood test. But that’s not how blood tests work, and here’s why. Routine blood tests only tell us what we ask them to look for.”
Dr Tannous went on to explain that standard blood tests typically check things such as white blood cells, kidney and liver function, cholesterol levels, and blood sugar, as well as the thyroid and inflammatory markers like CRP, or C-reactive protein, a chemical produced by the body in response to inflammation, reports the Mirror.
She added: “These are incredibly useful for giving us an overview of your general health but they don’t screen for everything, and they don’t automatically detect cancer. Some cancers don’t show any changes on these routine markers at all.
“Others may show subtle hints, like low haemoglobin (sign of slow blood loss), [and] raised inflammatory markers. But these findings are non-specific meaning they can be caused by many different, far more common conditions.
“We can test for tumour markers, but they are not part of routine blood tests, most are not screening tools, [and] they are only added when a healthcare professional has a specific reason, based on your symptoms, examination, or medical history.
“That’s why normal routine blood tests don’t always mean nothing is happening, and why symptoms always guide the investigations not the other way around. Blood tests are a tool, not a crystal ball.”
TikTok users responded with varied reactions in the comments section. One person commented: “The GPs need to understand this misconception! Every time I go with a problem they do bloods says every thing is fine and send me away. If I argue it they look at me like I’m crazy.”
Another person posted: “What’s the logic behind a ‘routine’ blood test? Why not always test for other matters which might not be suspected at that stage, for completeness and avoidance-of-doubt?”
Someone else remarked: “Well then maybe tumour markers should be part of routine blood tests, it’s not rocket science.”
A further user commented: “l always think a blood test is just a way of getting rid of a patient. It comes back with ‘nothing’ on it and the feedback, ‘nothing wrong with you’ and you are left wondering what is wrong?”
Others shared their own experiences. One said: “I had kidney cancer and all my blood test came back normal. Only diagnosed by an ultrasound and I was sent for that because the doctor thought it was a problem with my gallbladder. Thank god they checked while doing the gallbladder.”
Another wrote: “My partner had stage 4 bowel cancer and up to the weeks leading up to his passing all his bloods apart from iron and his white blood count during active chemo were fine. Never even elevated CEA (Carcinoembryonic Antigen) levels. Drs always said based on his bloods they wouldn’t have suspected he was as poorly as he was.”
The NHS explains that blood tests are typically performed to assess your overall wellbeing, determine whether symptoms you’re experiencing stem from particular conditions, establish if you’re at higher risk of developing a condition, or evaluate how effectively a condition is being treated or managed. Various types of blood tests exist depending on the specific condition being investigated.
