Type of test Stool
Normal findings
Normal intestinal flora
Test explanation and related physiology
Normally, stool contains many bacteria and fungi. The more common organisms include Enterococcus, Escherichia coli, Proteus, Pseudomonas, Staphylococcus aureus, Candida albicans, Bacteroides, and Clostridium. Bacteria are indigenous to the bowel. Sometimes normal stool flora can become pathogenic if overgrowth of the bacteria occurs as a result of antibiotics (e.g., Clostridium difficile), immunosuppression, or overaggressive catharsis. Salmonella, Shigella, Campylobacter, Yersinia, pathogenic E. coli, Clostridium, and Staphylococcus are acquired bacteria that can infect the bowel. Parasites also may affect the stool. Common parasites are Ascaris (hookworm), Strongyloides (tape worm), and Giardia (protozoans). Identification of any of these pathogens in the stool incriminates that parasite as the etiology of the infectious enteritis.
Infections of the bowel from bacteria, virus, or parasites usually present as diarrhea, excessive flatus, and abdominal discom fort. Patients who have been drinking well water, have been on prolonged antibiotics, or have traveled outside of the United States are especially susceptible.
Interfering factors
• Urine may inhibit the growth of bacteria. Therefore urine should not be mixed with the feces during collection of a stool sample.
• Recent barium studies may obscure the detection of parasites.
* Drugs that may affect test results include antibiotics, bismuth, and mineral oil.
Procedure and patient care
Before
* Explain the method of stool collection to the patient. Be matter of fact to avoid any embarrassment to the patient.
* Instruct the patient not to mix urine or toilet paper with the stool specimen.
* Instruct the patient to use an appropriate collection container.
During
* Instruct the patient to defecate into a clean bedpan.
• Place a small amount of stool in a sterile collection container.
• Send mucus and blood streaks with the specimen.
• If a rectal swab is to be used, wear gloves and insert the cotton-tipped swab at least 1 inch into the anal canal. Then rotate the swab for 30 seconds and place it into the clean container.
Tape test
• Use this test when pinworms (Enterobius) are suspected.
• Place clear tape in the patient’s perianal region. (This is especially helpful in children.)
• Because the female worm lays her eggs at night around the perianal area, apply the tape before bedtime and remove it in the morning before the patient gets out of bed.
• Press the sticky surface of the tape directly to a glass slide and examine microscopically for pinworm ova.
After
• Handle the stool specimen carefully as though it were capable of causing infection.
• Indicate on the laboratory slip any antibiotics that the patient may be taking.
• Promptly send the stool specimen to the laboratory. Delays in transfer of the specimen may affect viability of the organism.
• Note that some enteric pathogens occasionally take as long as 6 weeks to isolate.
• When pathogens are detected, maintain isolation of the patient’s stool until therapy is completed.
Abnormal findings
- Bacterial enterocolitis
- Protozoan enterocolitis
- Parasitic enterocolitis
