Q. Can blood cause dark-brown flecks in stool?

Answered by
Dr. Divakara P
and medically reviewed by Dr. Divya Banu M
Published on Dec 14, 2019

Hello doctor,

I have noticed dark (do not know if they are dark-brown, more greenish, or black) flecks in what looks like otherwise very normal stool. Can this be blood, or does blood typically only present as fully-black, tarry stool? Also, I have PKU, and my supplemental food contains 4g Ferrous Sulfate per serving. Could this cause discoloration in my stool from time-to-time?I am 43 years old with a history of anxiety, 6'2", 190, decent health. Non-smoker. Light drinker. In no pain.

Dr. Divakara P

Diabetology Endocrinology General Medicine Internal Medicine Pain Medicine Pulmonology (Asthma Doctors)


Welcome to icliniq.com.

Once in a while these kind of dark flecks is normal but if it is persistent then it is abnormal. Also, Ferrous Sulphate can cause blackish discoloration of stools. Blood in stools need not always be fully black, tarry stools but I strongly feel that it is due to Ferrous Sulfate. Still, I advise you get a test called Stool for Occult Blood. This test will detect any blood in your stool. If it comes positive revert back to me as you may require further tests.

Thank you doctor,

I did want to follow up with this: I do not so much tend to notice any of the flecks in the toilet. I notice these things more on the toilet paper. They sometimes very much appear to be undigested food (I tend to have nervous bowels and there is a huge history of IBS on my mother'ss

side of the family), but even when they don't so much appear to be undigested food, I'm only noticing them on the toilet paper. I have, in the past, passed dark stool, but rarely, and without accompanying pain, and almost every time it's happened, I've been able to think of dietary reasons. (along with my PKU diet, I'm allowed fruits, veggies, and junk food, and I I tend to eat a fair amount of chocolate-y things). Anyway, my whole point was that, with the flecks, I only notice them when I wipe. I guess, I'm wondering, also, isn't it very natural that stool can exit our body in a variety of dark and light shades of brown as well? Thanks again, so much, Chris

Dr. Divakara P

Diabetology Endocrinology General Medicine Internal Medicine Pain Medicine Pulmonology (Asthma Doctors)


Welcome back to icliniq.com.

Definitely I agree with you that the stool color can vary from slight yellow to dark brown, and there may not be any abnormality in your stools. But still it is better that we rule out blood in your stool as it is important and can be tested very easily. So, I advise you get stool for occult blood test done and revert back with report. There is no relation between nervous bowel or IBS and dark color of your stools. I also advice you stop taking tablet Ferrous Sulfate for one week and observe your stool color. Stool color persist to be dark even after stopping Ferrous Sulfate for about a week, then revert back.

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