Constipated black stools should first be ruled out as a result of diet, such as eating animal liver, chicken blood, pig blood, or taking medications such as bismuth potassium citrate. Next, consider rectal lesions such as internal hemorrhoids and anal fissures, and also consider bleeding in the upper gastrointestinal tract, such as gastric ulcers, duodenal ulcers, and gastric cancer.
Patients with constipation have enough time for the blood in the GI tract to mix with the stool because the stool stays in the intestine for too long.
Secondly, patients with constipation often have lesions of the rectal tract, such as internal hemorrhoids, anal fissures, and other diseases. On the one hand, the varicose veins around the anus rupture and bleed, mixing with feces and leading to black stools. On the other hand, the perianal disease causes the patient’s constipation symptoms to worsen, and the two are mutually beneficial.
For young adults, bleeding gastric and duodenal ulcers need to be considered, often accompanied by stomach pain and acid reflux and heartburn symptoms. In older patients with a previous history of constipation, disease caused by tumors of the digestive system needs to be highly suspected.