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The stool guaiac test involves fasting from iron supplements, red meat (the blood it contains can turn the test positive), certain vegetables (which contain a chemical with peroxidase properties that can turn the test positive), and vitamin C and citrus fruits (which can turn the test falsely negative) for a period of time before the test.
Fecal occult blood testing (FOBT), as its name implies, aims to detect subtle blood loss in the gastrointestinal tract, anywhere from the mouth to the colon.Positive tests ("positive stool") may result from either upper gastrointestinal bleeding or lower gastrointestinal bleeding and warrant further investigation for peptic ulcers or a malignancy (such as colorectal cancer or gastric cancer).
A multi-target stool DNA test was approved in August 2014 by the FDA as a screening test for non-symptomatic, average-risk adults 50 years or older. [8] A 2017 study found this testing to be less cost effective compared to colonoscopy or fecal occult blood testing. [9]
A lower gastrointestinal bleed is defined as bleeding originating distal to the ileocecal valve, which includes the colon, rectum, and anus. [2] LGIB was previously defined as any bleed that occurs distal to the ligament of Treitz, which included the aforementioned parts of the intestine and also included the last 1/4 of the duodenum and the entire area of the jejunum and ileum. [1]
Blood in stool looks different depending on how early it enters the digestive tract—and thus how much digestive action it has been exposed to—and how much there is. The term can refer either to melena, with a black appearance, typically originating from upper gastrointestinal bleeding; or to hematochezia, with a red color, typically originating from lower gastrointestinal bleeding. [6]
The stool guaiac test (or guaiac fecal occult blood test) is conducted to detect the presence of blood in stool that is not apparent to the unaided eye. The main pathogens that are commonly looked for in feces include: Bacteroides species; Salmonella and Shigella; Yersinia tends to be incubated at 30 °C (86 °F), which is cooler than usual
Diagnosis is often based on direct observation of blood in the stool or vomit. Although fecal occult blood testing has been used in an emergency setting, this use is not recommended as the test has only been validated for colon cancer screening. [19] Differentiating between upper and lower bleeding in some cases can be difficult.
The examiner will look for any scarring or masses that may indicate cancer or another disease. Typically, a rectovaginal examination is performed to assess pelvic pain, rectal symptoms, or a pelvic mass. It can also provide a sample for fecal occult blood testing, but is controversial for this purpose (see below). [1] [2] [3] [4]