Melena indicates the bleed is proximal to the ileocecal valve. Maroon stools can be either from a rapid small bowel transit or a colonic bleed. Hemorrhoids do not imply etiology. Use guaiac cards. Black stools can result from Pepto-Bismol, iron, charcoal, and spinach.
Red stools can result from beets.
These are preferable if the situation warrants. Saline, lactated Ringers, or Hespan can be substituted until blood products are available. In extreme situations non-crossmatched O negative blood may be used. Transfusion therapy should at least keep pace with an actively bleeding patient. If the patient's mental status is depressed consider endotracheal intubation.