STOOL IS COLLECTED to determine the presence of blood, ova and parasites, bile, fat, pathogens, or substances such as ingested drugs. Additional studies include fecal urobilinogen, nitrogen, Clostridium difficile, fecal leukocytes, calculation of stool osmolar gap, food residues, and other substances requiring lab evaluation. Gross examination of stool characteristics, such as color, consistency, and odor, can reveal such conditions as gastrointestinal bleeding and steatorrhea (excess fat in feces).
Stool specimens are collected randomly or for specific periods, such as 24 to 72 hours. Some stool collections require the patient to follow a specific diet or refrain from taking certain medications before the collection. Thorough and accurate patient education regarding a specific stool study prior to collection greatly increases the accuracy of the study results. Because stool specimens can't be obtained on demand, proper collection requires careful instruction to the patient to ensure an uncontaminated specimen. Fecal occult blood testing (FOBT) is one of the most commonly performed stool tests. It can be useful in initial screening for several disorders, although it's used more frequently in early cancer detection programs. FOBT can be performed at the bedside, in the lab, or at home. Because there's a risk for false-positive or false-negative results, patient preparation and specimen collection must be followed explicitly (see Factors that can interfere with FOBT).
What you'll need
To get started, collect the following equipment:
* specimen container with lid
* gloves
* two tongue blades
* paper towel or paper bag
* bedpan or portable commode
* two patient-care reminders (for timed specimens)
* lab request form and lab biohazard transport bag.
How it's done
First, explain the procedure to the patient and his family, if possible, to ensure their cooperation and prevent inadvertent disposal of timed stool specimens.
To collect a random specimen:
* Tell the patient to notify you when he has the urge to defecate. Have him defecate into a clean, dry bedpan or commode. Instruct him not to contaminate the specimen with urine or toilet tissue.
* Put on gloves.
* Using a tongue blade, transfer the most representative stool specimen from the bedpan to the container, and cap the container. If the patient passes blood, mucus, or pus with the stool, include this with the specimen.
* Wrap the tongue blade in a paper towel and discard it. Remove and discard your gloves, and wash your hands thoroughly to prevent cross-contamination.
To collect a timed specimen:
* Place a patient-care reminder stating SAVE ALL STOOL SAMPLES over the patient's bed and in his bathroom.
* After putting on gloves, collect the first specimen, and include this in the total specimen.
* Obtain the timed specimen as you would a random specimen, but remember to transfer all stool to the specimen container.
* As ordered, send each specimen to the lab immediately with a lab request form or, if permitted, refrigerate the specimens collected during the test period and send them when collection is complete. All specimens must be stored and transported in an approved lab biohazard container.
* Remove and discard gloves.
* Make sure the patient is comfortable after the procedure and he has the opportunity to thoroughly clean his hands and perianal area. It may be necessary for you to assist the patient with perineal care.
* Document the date and time of the specimen collection in the patient's medical record along with instructions that the patient can resume his normal diet and medication regime unless otherwise specified.
Special considerations
If stool must be obtained with an enema, use only tap water or normal saline solution. Never place a stool specimen in a refrigerator that contains food or medication to prevent contamination. Notify the healthcare provider if the stool specimen looks unusual.
Factors that can interfere with FOBT
False-positive results
Drugs and substances that may cause a false-positive FOBT result include:
* aspirin
* steroids
* indomethacin
* nonsteroidal anti-inflammatory drugs
* boric acid
* bromides
* colchine
* iodine or povidone-iodine.
Foods that may cause a false-positive result include:
* red meats, including processed meats and liver
* vegetables and fruits with peroxidase activity, such as turnips, horseradish, mushrooms, broccoli, radishes, apples, bananas, and cantaloupe.
False-negative results
Substances that may cause a false-negative result include:
* ascorbic acid (vitamin C) in excess of 250 mg/day
* iron supplements that contain over 250 mg vitamin C.
Other factors affecting test results
* bleeding hemorrhoids
* specimen collecting during menstrual period
* hematuria (blood in urine)
* toilet bowl cleansers.
Selected references