Melaena passage of tarry black stool due to the presence of altered blood.
60 ml or more of upper Gl bleed lead to melaena
One episode of upper Gl bleed produce 5 to 7 days of melaena
Blood should remain in the gut for 4 hrs or more to produce Melaena
Upper gastrointestina bleed and LGI bleed proximal to middle of transverse colon result in Melaena.
