<s>[INST] hi, i am 34 years old. i had a occult blood test for colorectal cancer screening because of family history. 3 samples were taken in 3 different days. the first and third samples were weakly positive . but the second sample was positive (+2). one day before the second sample i eat tomato and carrots.... also i take omeprazol before second sample. could i trust to the result of this test?? or is it necessary to repeat the test?? the CEA (antigen) test could help to the diagnostic process? [/INST] for screening purposes colonoscopy is best. now a days Circulating tumour cells tests have come up.but you should go with colonoscopy first. CEA is not good for screening as it can be raised in many other conditions also </s>