A qFIT test is a "quantitative" analysis performed in a laboratory to quantify the amount of blood present in a stool sample. This is what the NHS and every other country uses for bowel cancer screening / testing. If this test demonstrates blood in the stool you would go for a colonoscopy.
In contrast, at-home "FIT" tests are a type of lateral flow test. They are not "quantitative" - i.e. they don't give a numeric result of the amount of blood in the stool. They are a similar technology to a COVID lateral flow test - you need to look for the presence or absence of a line on the cassette to read if the result is "positive" or "negative".
These devices are not suitable and should not be used:
- They tend to be less sensitive for the detection of blood than lab-based qFIT test.
- Reading the result is very prone to error - as you'll probably have experienced if you've ever squinted at a COVID lateral flow test trying to figure out if there is a line there or not. A lab based qFIT test gives you a number - there's no ambiguity.
- Most importantly, these tests have not been assessed for bowel cancer screening - i.e. we have no data from trials validating that they work. In contrast we have a lot of trial data validating the use of lab-based qFIT tests for bowel cancer screening.
- There's significant variation in quality from manufacturers with very little regulatory oversight. All lab-based testing in the UK is regulated by UKAS and standards have to be met. So you can have confidence that a qFIT test in a lab is the same whichever lab you use.
So all-in-all, lateral flow at-home "FIT" tests are dangerous and you should not trust something as important as ruling out cancer to them.
Additional link to a recent article from the BBC about lateral flow PSA tests: https://www.bbc.co.uk/news/articles/cgl00gn15y8o.
The same concerns apply to lateral flow at-home "FIT" tests.