The commonest way a screening programme loses a cancer is not a missed test — it is a positive result answered with another test. A positive faecal immunochemical test has done its job; repeating it, adding a stool culture, or treating presumed haemorrhoids and rechecking in three months all achieve the same thing, which is delay.
The corollary is equally firm. A negative faecal test in a patient with iron deficiency anaemia, a change in bowel habit lasting weeks, rectal bleeding or unintended weight loss does not exclude colorectal cancer, and was never designed to. The test is for asymptomatic screening; symptoms take a patient out of the screening pathway and into a diagnostic one.
Two other things to settle at that appointment. Check the ferritin and full blood count — iron deficiency changes the urgency and may point to a second lesion. And record what the patient was told, because the reason positive tests go unfollowed is most often that the patient did not understand that a positive result was a positive result.
- A positive faecal immunochemical test goes to colonoscopy, never to a repeat faecal test
- A negative test does not exclude cancer in a symptomatic patient
- Check ferritin and full blood count at the same visit
- Confirm the patient understands that the result was abnormal, and record that you did
- Attributing rectal bleeding to haemorrhoids without examining the rest of the colon is the classic missed diagnosis
Why it matters
Screening programmes lose most of their cancers between the positive result and the colonoscopy, not at the test itself.
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