Black stool after a blood transfusion: what to know

A transfusion does not normally travel through the digestive tract and turn stool black. Dark, sticky, unusually foul-smelling stool can mean blood has been digested higher in the stomach or bowel. A gastritis or peptic ulcer can bleed, and Helicobacter Pylori Infection is one possible contributor to stomach irritation or ulcer disease. Iron tablets, bismuth medicines and some foods can also darken stool without bleeding. The appearance, timing, medicines, symptoms and the reason for the transfusion all matter.

Tell the clinical team that you have noticed black stool, especially if the transfusion was recent or you are still in hospital. Do not stop prescribed medicines without advice, but mention iron, aspirin, anti-inflammatory painkillers and blood-thinning treatment. Note when the colour began, how many bowel movements you have had and whether the stool was sticky or tar-like. A clinician may check your pulse and blood pressure, examine you, and arrange blood tests or other tests based on your symptoms.

Seek emergency help now for fainting, severe weakness, confusion, breathlessness, chest discomfort, a fast heartbeat, vomiting blood or repeated black stools. These symptoms can accompany significant blood loss. Even without them, contact the transfusion service or a healthcare professional promptly if the stool is tar-like, continues, or you cannot explain the colour.

Could my medicines or iron explain the colour? Do I need blood tests or assessment for bleeding? Should I change any painkiller or blood thinner? What symptoms should make me return immediately?