No.......they can't.
Occult blood in the stool ( Test for colon cancer) if positve is a sign of polyps or cancer, HOWEVER...a negative test does not exclude the diagnosis.
Why? because the test only tests for disease in the rectum and descending colon, the ascending and transverse colon harbouring a tumour will not be detected.
Have you test, but if your result is negative on faecal testing and you still have abdominal bloating or pain, then you may still have colonic growths...polyps or cancer.
So JJ in answer to your question...NO...they cannot test PROPERLY with a little poo on the card.