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In the emergency, for Melena (black tarry stools) they only perform basic tests like a full blood count to see the degree of blood loss and whether there is any need for blood transfusions
(if Hb < 7 g/dL) or supplements to improve the hemoglobin (if between 7-10 g/dL). Other than that the stool is sent for routine examination to see if it is really altered blood from the stomach that is causing the melena (black tarry stool).
Pepto bismol is actually an ant acid, it contains bismuth salicylate and is used to protect the stomach lining and yes, it can cause black stool by giving stool a black color owing to its contents not by harming the stomach or causing an Upper GI bleed.
Going to the emergency is your decision but I do not think it will be of much help then it was last time since, they will follow their protocols and prescribe the same treatment again.
Ulcers in the large gut are rare and they do not cause black tarry stools. Black tarry stools is a sign of upper GI bleeds.
However, you can urge them to get you an early with a Gastroenterologist so that an Upper GI endoscopy (indicated in your case) can be done and tests for H pylori can be ordered. Once the tests show presence of H pylori you can be prescribed the triple regimen to eradicate the H pylori.
If you think you are having too much of black tarry stools and stomach symptoms like pain that is out of proportion, then you can go the ER for a re-evaluation.
Hope this helps.
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