Written by Dr Clive Price (MRCGP UK) Founder of True Proactive practicing GP at Tara Road Medical practice, advocate for proactive medicine. Healthpoint
FIT vs FOBT, what is the difference and why True Proactive's FIT is preferred
Bowel cancer screening tests look for small microscopic traces of blood in the stool that would usually be invisible to the human eye, with the rationale that bowel cancers and some polyps tend to bleed. The aim of screening is to detect bowel cancers before they develop symptoms. Generally the earlier a bowel cancer is detected the easier it is to treat. There are two main types used worldwide
- FOB test which is the older guaiac based test
- FIT which is the newer faecal immunochemical test – the same test that True Proactive fit test uses.
Most modern screening programmes now use FIT because it is more accurate, easier for patients, and better supported by evidence. I have seen pharmacies in NZ selling cheap inaccurate FOB tests, I explain later in this article why I think this is dangerous.
How the tests work
FOB test
The older guaiac based test detects blood using a chemical reaction. It is not specific to human blood and results can be affected by diet and some medications. It often requires multiple stool samples. Humans tend to be meat eaters, hence the increased false positive rates with the FOB tests – a user could have a positive result simply because it picked up animal haemoglobin in the users diet.
FIT test
FIT uses antibodies that detect human haemoglobin only. This makes it more specific to bleeding from the bowel. FIT usually requires just one sample and has no dietary restrictions. The FIT test can also give quantitative numbers, ie not just a positive or negative, making it more accurate.
Accuracy and Performance of both tests
FIT has been shown in large evidence reviews to detect bowel cancer more reliably than older FOBT methods. At commonly used screening thresholds
- One study published in the BMJ suggested FIT tests can detect up to 97% of colorectal cancers, at a threshold of 2 µg Hb/g
- FOBT detects closer to 50-60%
FIT also performs better at detecting higher risk polyps although no stool test finds all polyps, polyps are small lesions in the bowel that over time can grow into cancers.
Why screening programmes now use FIT
One simple sample rather than multiple needed • No diet changes needed • Better cancer detection • Higher completion rates • Adjustable thresholds to balance accuracy and follow up testing • Less false positives
What a positive FIT result means
A positive FIT means blood was detected above a set threshold. It does not diagnose cancer. Further investigation such as colonoscopy is needed.
A negative FIT does not rule out bowel cancer, but it does mean there has been no microscopic blood found in your stool at the time of testing, this is a very reassuring finding, however as with any test it is not 100%. Thats why we recommend keeping an open mind about your global health situation and working with your GP.
Are pharmacy FOB tests safe and reliable
In New Zealand some pharmacies and online retailers sell low cost FOB tests that use the older technology as discussed. While these tests may appear convenient, they are not equivalent to modern FIT screening and can give misleading reassurance or unnecessary alarm.
I am particularly concerned as these pharmacies and products themselves tend to give little or no counselling or education regarding the limitations of these tests.
A false negative result is particularly concerning. This occurs when bleeding is present but not detected by the test, patients may be reassured that they have had a negative test, unaware they may still have cancer. Potentially delaying further investigation and diagnosis. In bowel cancer screening, delay matters.
That is why I started True Proactive and have really tried to educate people about the difference between FOB and FIT tests and also that all tests have limitations.
From a clinical perspective, offering outdated FOB tests directly to the public without clear explanation of their limitations or risks, undermines early detection. Screening should reduce risk, not create false reassurance.
If you are choosing to screen privately, it is important to understand exactly which test you are using and whether it reflects current best practice, I would always recommend a FIT test rather than a FOB test to my patients.
Summary
FIT is the modern evolution of stool based bowel screening. Compared with older FOBT tests it is more specific, sensitive, easier to complete, and better supported by current evidence. This is why it has replaced FOBT in many national screening programmes, including the NZ national bowel screening programme. The True Proactive FIT test uses this modern lab processed technology rather than the outdated FOB tests sold in some pharmacies.
It is for that reason that i always recommend a FIT test to my patients who want to safely and reliably screen for bowel cancer. You can get started today with the True Proactive FIT Test.
Thanks for reading Dr Clive Price 26/03/2026
