Final answer:
Black and tarry stools, or melena, suggest upper gastrointestinal bleeding, possibly from peptic ulcers, gastritis, or esophageal varices, and can also be a sign of colorectal cancer or infections. A physician will likely order a stool sample to help diagnose the cause.
Step-by-step explanation:
A patient reporting black and tarry stools, which is medically referred to as melena, should be evaluated for several conditions. Such stools can indicate bleeding in the upper gastrointestinal tract, which may be due to peptic ulcers, gastritis, or esophageal varices. Additionally, other potential conditions include colorectal cancer and infections that can cause bloody stools such as those from C. jejuni, Salmonella, and E. histolytica. In some instances, taking certain medications or supplements, like iron, can also lead to black stools. To diagnose the underlying cause, a physician may order a stool sample to check for the presence of blood and possible causative agents.
Colorectal cancer may present with black tarry stools due to rectal bleeding, which can be either obvious or occult. Vital to cancer prevention, a colonoscopy can identify and remove precancerous polyps in the colon. In addition, upper gastrointestinal bleeding should be considered, which can arise from conditions like peptic ulcers or gastritis, both of which can lead to the characteristic black, tarry stools due to the presence of digested blood.