After a sample reaches the laboratory, a chemical (usually guaiac) is applied. If the chemical comes into contact with blood, it will appear as a different color.  Once the sample is analyzed, the physician will contact the patient with the results.

If the test results are negative, no blood was found in the sample. A positive result indicates that blood was found. Patients should remember that several factors – including foods and medicines consumed before the test – may skew the accuracy of test results.

Positive test results will lead to further testing to determine the cause of the bleeding. Tests that may be performed include:

• Colonoscopy. Examination of the entire colon with a long tube and camera that is inserted into a patient’s rectum.
  
  
• CT colonography (virtual colonoscopy). Uses computed tomography to produce detailed pictures of the colon. The test is noninvasive but is not as sensitive as a colonoscopy and does not allow physicians to collect biopsy samples. Nevertheless, it may be the preferred test for some patients with gastrointestinal conditions.
  
  
• Flexible sigmoidoscopy. Similar to a colonoscopy, this procedure uses a shorter tube to investigate the lower parts of the colon (sigmoid colon and descending colon). In some cases, this test will be performed in conjunction with the original FOBT.
  
  
• Double contrast barium enema (DCBE). A chalky substance is used to open and fill the colon. Air is then pumped in to expand the colon, and x-rays are taken.
  

In some cases, other tests may be performed that allow the physician to look inside esophagus, stomach and duodenum, which are potential sources of bleeding. These include:

• Upper endoscopy
• Upper gastrointestinal x-ray
• Small bowel x-ray