Sometimes you can't. Intestinal shed is generally, pinkish orangy. IF blood is present it's usually a much brighter red. Very occasional intestinal shed may be nothing to worry about. If you see blood, then that's concerning. If there is a lot of intestinal shed, or it's happening a lot, then I would look for a cause. Other internal parasites (roundworm, etc) can cause increased intestinal shed. If there is a lot, it's mucousy, runny, or bloody, then I would treat for coccidiosis, especially if the bird is lethargic, sleepy, not eating or drinking, sitting fluffed up. Coccidiosis is more common in chicks and young birds. Older birds can still have issues if moved to new ground or new birds are brought in and they are exposed to new strains they've never been exposed to, or if immune systems are compromised by another health issue. Most older birds that don't fall in those categories have some resistance to the strains they've been exposed to and won't get sick. If the bird seems normal then I'd suggest getting a fecal done to check for internal parasites, see if it's one of those. The fecal will also look for coccidia.