(Study type: Fecal analysis; unpreserved stool specimen collected in dry, clean, covered container. The laboratory should be contacted if there are questions regarding adequacy of specimen volume; related body system: Digestive and immune systems.)

General Evaluation

Feces consist mainly of cellulose and other undigested foodstuffs, bacteria, and water. Other substances normally found in feces include epithelial cells shed from the GI tract, small amounts of fats, bile pigments in the form of urobilinogen, GI and pancreatic secretions, electrolytes, and trypsin. Trypsin is a proteolytic enzyme produced in the pancreas. The average adult excretes 100 to 300 g of fecal material per day, the residue of approximately 10 L of liquid material that enters the GI tract each day. The laboratory analysis of feces includes macroscopic examination (volume, odor, shape, color, consistency, presence of mucus), microscopic examination (leukocytes, epithelial cells, ova and parasites, meat fibers), and chemical tests for specific substances (occult blood, trypsin, estimation of carbohydrate).

Occult Blood

Detection of occult blood is the most common test performed on stool. The prevalence of colorectal adenoma is greater than 30% in people aged 60 yr and older. Progression from adenoma to cancer occurs over a period of 5 to 12 yr and from cancer to metastatic disease in 2 to 3 yr.

Bacterial Pathogens and Intestinal Parasites

Routine fecal analysis also evaluates stool for the presence of bacterial pathogens and intestinal parasites and their eggs. Some parasites are nonpathogenic; others, such as protozoa and worms, can cause serious illness. The American Society for Clinical Pathology and the American Academy of Family Physicians support recommendations against routine stool testing for community-acquired GI pathogens in patients who are hospitalized and develop diarrhea after the third day of hospitalization. The rationale is that the test methods in use have been developed to identify pathogens commonly associated with community-acquired GI infections, which for the most part are self-limited upon appropriate treatment; treatment is focused on preventing and reversing dehydration.

Exceptions may include:

• Testing for Clostridioides difficile in patients over 2 yr of age if they develop diarrhea after the third day of hospitalization
• Testing for older adults and immunocompromised patients who may still harbor community-acquired pathogens and develop diarrhea after the third day of hospitalization

Calprotectin

Calprotectin is a nonspecific indicator of the presence of granulocytes (mostly neutrophils) in stool. Granulocytes are WBCs whose cytoplasm contains granules that secrete proteins, including calprotectin, and other chemicals into the intestinal mucosa when activated by an inflammatory process. Calprotectin crosses the epithelial barrier and enters the gut, where it is absorbed by the feces and excreted. The amount of calprotectin in stool is somewhat proportional to the number of neutrophils in the intestinal mucosa and is an indicator of the degree of intestinal inflammation. Calprotectin is largely used as part of the diagnostic investigation of various inflammatory bowel diseases (IBDs), notably Crohn disease and ulcerative colitis. It can also be elevated in colon cancer and GI infections. Calprotectin levels are normal in patients with irritable bowel syndrome.

Screening tests for colon cancer

Hemoccult test for occult (hidden) blood in the stool is often performed at home; pretesting dietary and medication restrictions are necessary as described in the test instructions. Small samples of stool, from separate samples over the course of 3 days, are placed on special cards that contain a reagent called guaiac. The kits can be obtained with or without a prescription. Once the samples have been collected, they can be sent by mail either to the requesting health-care provider (HCP) or to laboratory for testing. The test procedure is simple: A solution of hydrogen peroxide added to each test card. If blood is present, the peroxide reacts with the blood and guaiac and causes the stool sample to change to a blue color. The hemoccult test is also called gFOBT, guaiac smear test, and stool guaiac test.

Fecal immunochemical test (FIT) is another more sensitive immunochemical test for occult blood in stool than the hemoccult test. It can be obtained with or without a prescription, requires a single sample, and does not require dietary restrictions, as it detects only human blood. Once the samples have been collected, they can be sent by mail either to the requesting HCP or to laboratory for testing.

Multitargeted stool DNA (mt-sDNA or stool DNA (Cologuard) is a combination of stool DNA detection and FIT occult blood detection. The test kit can be obtained by prescription from a HCP or from Cologuard online through a telemedicine provider. Sample collection is done at home; once the samples have been collected, they are returned to the Cologuard company for testing.

Laboratories are also developing colon cancer–specific liquid biopsy studies. Liquid biopsy is a term used to describe a test performed on blood or body fluid and is used to identify DNA from tumor cells, such as those associated with colon cancer. Blood-based tests have the potential to increase compliance in regular screening for colon cancer, especially for patients who have an aversion to handling stool. Currently there are two U.S. Food and Drug Administration–approved blood tests available for colorectal screening in people who are at average risk for developing colon cancer. For additional information regarding blood-based tests for colorectal cancer, refer to the study titled “Colonoscopy.”

Rotavirus

Rotavirus, a double-stranded RNA virus in the family Reoviridae, has more than 40 known serotypes worldwide, 6 of which are prevalent in the United States. The two structural proteins, protease-cleaved protein (P protein) and glycoprotein (G protein), make up the outermost layer of the virus’s capsid. The gene segments that produce P and G proteins are known to assort independently, and the protein recombinations are used to define the different serotypes and to develop vaccines against the virus. The name rotavirus is a Latin derivation of rota, or “wheel,” which describes the wheel-like appearance of the virus as seen by electron microscopy.

Rotavirus gastroenteritis (RGE) is the major cause of severe GI inflammation in children under 2 yr of age; studies have predicted that all children will be infected by rotavirus by age 5 yr. Older adults, especially those living in long-term residential facilities and patients of any age who are immunocompromised, are also susceptible to infection. The disease is highly contagious. It is transmitted by the fecal-oral route through direct person-to-person contact or handling of fomites (inanimate objects, such as toys, magazines, etc., that can transmit disease). Symptoms begin to appear within 1 to 3 days after exposure. Symptoms include fever, vomiting, and severe diarrhea, which lasts about 7 days; some patients also experience abdominal pain. Infections generally peak in the cooler, dryer months of the year. Vulnerable individuals can be reinfected multiple times during their lives, most likely by different viral serotypes. The development of natural immunity over time makes subsequent infections less severe, which is why healthy adults are rarely affected.

There are two oral rotavirus vaccines currently licensed for use in the United States. The Centers for Disease Control and Prevention recommends that all doses of vaccine be given before age 8 mo. RotaTeq (RV5) is given in three doses at ages 2, 4, and 6 mo; Rotarix (RV1) is given in two doses at ages 2 and 4 mo. Childhood vaccinations can be somewhat controversial. As with other preventive health-care practices, all patients, parents, or caregivers should discuss the benefits and risks of this vaccine with their HCP before making a decision. Health situations that warrant a decision to forgo vaccination include allergic reaction to any given dose of the oral vaccine, known allergy to any component of the vaccine, diseases that affect the immune system (HIV/AIDS, severe combined immunodeficiency), or intussusception. Consideration to withhold the vaccine should be given to infants being treated with steroids or who are undergoing cancer treatment. Infants who are mildly ill may be given the vaccine, but vaccination for significantly affected individuals should be postponed until after recovery. Laboratory methods used to obtain results from stool specimens include EIA and molecular methods (multiplexed reverse transcriptase polymerase chain reaction [RT-PCR], semi-nested RT-PCR, nucleotide sequencing).

Clostridioides

Clostridioides difficile is a gram-positive, spore-forming bacterium that can cause a life-threatening bowel infection in patients who are susceptible or are receiving broad-spectrum antibiotic therapy (e.g., clindamycin, ampicillin, cephalosporins). C. difficile infection (CDI) is a major concern with respect to hospital-acquired infection (HAI) surveillance efforts. Older adults, especially those living in long-term health-care or residential facilities; children aged 1 to 3 yr; and those who are immunocompromised are most susceptible to infection. The bacteria release a toxin that causes necrosis of the colon tissue. The organism can be identified from a stool culture (see the study titled “Culture, Bacterial, Various Sites”). It is important to distinguish C. difficile colonization from cytogenic C. difficile infection in patients with diarrhea of unknown cause. Colonization is often asymptomatic, so in these patients, the cause of diarrhea would warrant further investigation and different treatment from that administered for CDI. The presence of C. difficile in watery stool without evidence of the toxin or genes associated with toxin production does not provide the basis for diagnosis of CDI. Two toxins, A and B, are associated with toxigenic strains of C. difficile and can be identified more rapidly by using methods that do not involve stool culture.

Guidelines have been developed by the American College of Gastroenterology (www.gi.org), American Society of Microbiology (www.asm.org), CDC (www.cdc.gov), Infectious Diseases Society of America (www.idsociety.org), and Society for Healthcare Epidemiology of America (www.shea-online.org); the most current information is available on their respective websites. There is some general overlap in recommendations regarding testing for toxin-producing C. difficile. A two-step algorithm has been recommended that combines the rapid screen for GDH and toxins with confirmation by PCR or NAAT. The combination of test methods provides highly sensitive and specific results produced in a clinically relevant time frame. Screening test results that are all positive are interpreted as CDI infection likely. Screening test results that are all negative are interpreted as CDI infection unlikely. Screening test results that are mixed (GDH pos/Toxin neg or GDH neg/Toxin pos) are confirmed by PCR or NAAT.