Thank you for the query.
CEA level is used to control possible colon cancer
regrow or metastases appearance. If the person who has colon cancer history gets increased CEA level, possible metastases should be localized or ruled out.
So this should be the reason of concern. Moreover, B2 stage gives high rate of survivals so it is necessary and worth to keep looking.
The best way to do that is PET scan which will localize possible metastases. If this test is not available for your father, chest and abdominal CT with contrast should be performed.
Hope this will help.