Diagnostic Evaluation

Core Concepts

Stool specimen tests

• Occult (hidden) blood tests — such as fecal occult blood testing (FOBT) and fecal immunochemical testing (FIT) — detect tiny amounts of blood not visible to the eye. They are used for screening and for evaluating symptoms. Certain foods or medications can interfere with some versions of these tests, so follow the specific test's instructions (which items to avoid and for how long).
• Stool culture: A specimen is sent to the lab to grow bacteria and identify organisms causing diarrhea or infection.
• Ova and parasite (O&P) examination: Looks for parasites and their eggs, usually when a person has prolonged diarrhea, especially with a travel history.
• Other stool tests may be ordered for specific questions — for example, testing for a particular bacterial toxin in antibiotic-associated diarrhea, or measuring fat in the stool when malabsorption is suspected.
• Collection technique matters: Collect stool in a clean, dry container — never from toilet water — and avoid mixing it with urine. Label it, transport it promptly (some tests need to be kept cool or delivered quickly), and document it. If the patient is confused or incontinent, you may need to use a collection device that keeps stool separate from urine.

Imaging studies

• Abdominal X-ray: A quick picture that can show gas patterns, obstruction, or large amounts of stool in the colon.
• Barium studies: The patient swallows barium (upper GI series) or receives it through the rectum (barium enema) so the outline of the bowel shows up on X-ray. Barium is not absorbed, and the patient must pass it afterward — the nurse encourages fluids and monitors for the passage of the barium, because a blockage could occur if it hardens.
• CT, MRI, and ultrasound: Provide detailed images of the abdominal organs and bowel wall; some require fasting or drinking a contrast agent, and the preparation varies by facility protocol and provider order.
• Capsule endoscopy: The patient swallows a small camera that takes pictures as it travels through the tract, then passes it naturally — useful for viewing the small intestine, which is hard to reach with other tools.

Endoscopic procedures

• Colonoscopy: A flexible scope examines the entire large intestine. It requires the bowel to be empty, so the patient follows a clear-liquid diet and a bowel prep (laxative solution) that empties the colon — one of the most important nursing-teaching moments in this topic. The prep regimen, timing, and fasting rules follow the provider's order and the facility's protocol; they vary, so never quote a universal schedule.
• Sigmoidoscopy: Views the lower portion of the colon (the sigmoid colon and rectum); prep is less extensive than for colonoscopy.
• Anoscopy: A short scope examines the anal canal and lowest rectum.
• During and after: Endoscopy is often done with sedation, so the patient needs monitoring afterward — vital signs, level of consciousness, and watching for pain, bleeding, or fever. The nurse reports anything unusual to the provider immediately and explains that the patient should not drive or make important decisions for the rest of the day if sedation was used.

Preparation and aftercare: the nurse's checklist

Before any test, the nurse confirms the patient understands it, checks allergies and current medications with the care team, verifies the ordered prep, and documents that it was completed (for example, "clear liquid diet tolerated, bowel prep completed"). After the test, the nurse monitors for complications, explains the results when the provider has communicated them, and teaches the patient what to expect (such as gas and cramping after endoscopy, or the need to pass barium after a barium study). Any unexplained abdominal pain, heavy bleeding, or fever after a procedure is reported immediately.

Scope of practice and institutional variation

Exactly which preparation steps nurses perform — administering prep solutions, giving enemas, or inserting tubes for barium studies — varies by state nurse practice act, facility policy, and the nurse's education and competency validation. Delegation of tasks such as specimen transport is common, but patient teaching, assessment, and the decision to report findings are nursing responsibilities that are not delegated. When in doubt, follow the facility's procedure manual and ask the charge nurse or educator.

Common Confusions