Dear Dr. Roach: Why didn’t you recommend one of the at-home kits for the person with Lynch syndrome who had a bad reaction during her colonoscopy? I don’t ever intend to have another colonoscopy.

It is invasive, the prep is too much (yes, I understand why), and it takes up 24 hours of your time. — A.T.

Answer: Lynch syndrome, also called hereditary nonpolyposis colorectal cancer syndrome, is a condition that is caused by a genetic mutation in a DNA mismatch repair gene. Without this mismatch repair system, some cancers are much more likely, especially colon cancer. People with Lynch syndrome are at a much higher risk for colon cancer.

Cologuard and other at-home tests are not intended for and have not been tested in people with Lynch syndrome. Furthermore, people with Lynch syndrome quickly progress from having normal tissue to having cancer and may bypass the DNA sequences that the stool-based tests are designed to detect. Lynch-syndrome cancers are also preferentially on the right side of the colon, which is harder for Cologuard to detect.

People with Lynch syndrome should get a full colonoscopy every one to two years, beginning several years before the youngest family member was diagnosed or between ages 20-25 — whichever is earliest.

Cologuard is a good test for people who will not or cannot do a colonoscopy. I continue to get a colonoscopy as it’s a more sensitive test. Yes, the prep is unpleasant, but 24 hours of my time every 5-10 years is worth the improved detection from a colonoscopy to me. I take care of several gastroenterologists who also get colonoscopies for their own cancer screening.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu.