Stool specimen collection: nursing steps that change with the test ordered

Purpose: one specimen, several very different tests

Stool is tested for hidden blood, for bacteria by culture, for parasites by microscopy, and for Clostridioides difficile toxin or genes. Each test fails in its own way. A guaiac card can turn positive from red meat. A culture can miss pathogens if the sample sits too long. A C. diff test on formed stool from a client taking laxatives can label colonization as infection.

So the first nursing step is reading the order and the lab requirements: which container, whether a preservative vial is used, how many samples, and over how many days. Hand hygiene and gloves apply throughout, and the specimen is treated as potentially infectious.

Critical steps where errors happen

Contamination is the most common error. MedlinePlus guidance for cultures and parasite tests is consistent: do not let urine, toilet water or toilet tissue mix with the sample. Have the client void first, then catch stool in a clean container, a hat placed under the toilet seat, or plastic wrap over the bowl. For an infant, plastic wrap lining the diaper keeps urine separate.

Labeling and timing come next. Label the container at the bedside with the client's identifiers and the collection date and time, as MedlinePlus advises for parasite samples. For a fecal culture, MedlinePlus says to return the sample to the lab as soon as possible. Follow the lab's rule on refrigeration or preservatives rather than guessing, because the right handling differs by test.

Occult blood: guaiac cards versus FIT

For the guaiac test, MedlinePlus describes samples from three separate bowel movements, usually two smears from each, placed on the card and returned to the lab. Before or during collection, some kits ask the client to avoid red meat and certain raw produce such as cantaloupe, broccoli, turnip, radish and horseradish, and to avoid vitamin C above 250 mg a day and NSAIDs. Clients taking aspirin for heart protection should ask the prescriber rather than stop it.

FIT uses an antibody to human blood. MedlinePlus notes it needs one to three samples depending on the brand and no diet or medication changes. A positive result from either test means bleeding somewhere in the digestive tract, not cancer, and usually leads to colonoscopy.

Culture, parasites and C. diff samples

Parasites are not shed every day, so MedlinePlus says several samples over a few days may be needed for an accurate ova and parasite result. Space them as ordered rather than collecting three from one bowel movement. Cultures follow the same clean-catch steps with prompt delivery.

For C. diff, CDC advises testing when a client has three or more stools in 24 hours and laxatives or stool softeners have not been used, and it does not recommend repeat testing to prove cure once symptoms resolve, since many people stay colonized. A nurse who sends formed stool, or a sample from a client on scheduled laxatives, may produce a misleading result. Contact precautions start on suspicion and do not wait for the report.

Complications, documentation and a hypothetical item

Collection itself rarely harms the client, but a sample showing frank blood, black tarry stool or mucus is reported rather than only bagged. Document the test, time collected, stool color, consistency and amount, any diet or medication preparation, and when it went to the lab.

Hypothetical scenario, not a real exam item: a client collecting guaiac cards at home says, "I ate steak last night and took ibuprofen for a headache." The nurse should tell the client to check the kit instructions and contact the provider, because both can affect accuracy. Mailing the cards anyway, or adding vitamin C for health, both risk a wrong result.

Sources and further reading

MedlinePlus: Fecal Occult Blood Test (FOBT). gFOBT vs FIT, sample numbers, diet and drug restrictions including vitamin C over 250 mg and NSAIDs, aspirin for heart conditions, positive result and colonoscopy follow-up.

MedlinePlus: Stool guaiac test. Samples from three bowel movements, keeping urine out, foods and drugs that interfere with guaiac testing, FIT needing no diet changes.

MedlinePlus: Fecal culture and Ova and Parasite Test. Collection methods, no urine, water or tissue in the sample, plastic wrap in diapers, return to the lab as soon as possible; parasite testing page (medlineplus.gov/lab-tests/ova-and-parasite-test) supports labeling and several samples over days.

CDC: Clinical Overview of C. diff Infection. Test with three or more stools in 24 hours when laxatives or stool softeners were not used; repeat testing after resolution not recommended.