Stool Studies

OVERVIEW OF STOOL STUDIES

The elimination of digestive waste products from the body is essential to health. Excreted waste products are known as stool or feces. Stool examination is often done for evaluation of gastrointestinal (GI) disorders such as GI bleeding, GI obstruction, obstructive jaundice, parasitic disease, dysentery, ulcerative colitis, and increased fat excretion.

Stool is composed of the following materials:

Waste residue of indigestible material (e.g., cellulose) from food eaten during the previous 4 days
Bile (pigments and salts)
Intestinal secretions
Water and electrolytes
Epithelial cells that have been shed
Bacteria
Inorganic material, mainly calcium and phosphates
Undigested or unabsorbed food (normally present in very small quantities)

The output of feces depends on a complex series of absorptive, secretory, and fermentative processes. Normal function of the colon involves three physiologic processes: (1) absorption of fluid and electrolytes, (2) contractions that churn and expose the contents to the GI tract mucosa and transport the contents to the rectum, and (3) defecation.

The small intestine is approximately 23 feet (7 m) long, and the large intestine is 4 to 5 feet (1.2 to 1.5 m) long. The small intestine degrades ingested fats, proteins, and carbohydrates to absorbable units and then absorbs them. Pancreatic, gastric, and biliary secretions exert their effects on the GI contents to prepare this material for active mucosal transport. Other active substances absorbed in the small intestine include fat-soluble vitamins, iron, and calcium. Vitamin B₁₂, after combining with intrinsic factors, is absorbed in the ileum. The small intestine also absorbs as much as 9.5 L of water and electrolytes for return to the bloodstream. Small intestine contents (i.e., chyme, which contains fragments of proteins, droplets of fat, salt, and water) begin to enter the rectum as soon as 2 to 3 hours after a meal, but the process is not complete until 6 to 9 hours after eating.

The large intestine performs less complex functions than the small intestine. The proximal, or right, colon absorbs most of the water remaining after the GI contents have passed through the small intestine. Colonic absorption of water, sodium, and chloride is a passive process. Fecal water excretion is only about 100 mL/day. The colon mainly moves the luminal contents by seemingly random contractions of circular smooth muscle. Increased propulsive activity (i.e., peristalsis) occurs after eating. Peristaltic waves are caused by the gastrocolic and duodenocolic reflexes, which are initiated after meals and stimulated by the emptying of the stomach into the duodenum. The muscles of the colon are innervated by the autonomic nervous system. In addition, the parasympathetic nervous system stimulates movement, and the sympathetic system inhibits movement. Massive peristalsis (progressive waves of muscular contractions pushing the contents ahead) usually occurs several times a day. Resultant distention of the rectum initiates the urge to defecate. In persons with normal motility and a mixed dietary intake, normal colon transit time is 24 to 48 hours.

STOOL ANALYSIS

Stool analysis determines the various properties of the stool for diagnostic purposes. Some of the more frequently ordered tests on feces include tests for leukocytes, blood, fat, ova, parasites, and pathogens (Table 4.1). (See Chapter 7 for stool culture.) Stool is also examined by chromatographic analysis for the presence of gallstones. The recovery of a gallstone (precipitated by cholesterol or bile pigments) from feces provides the only proof that a common bile duct stone has been dislodged and excreted. Stool analysis also screens for colon cancer and asymptomatic ulcerations or other masses of the GI tract and evaluates GI diseases in the presence of diarrhea or constipation. Stool analysis is done in immunocompromised persons for parasitic diseases. Fat analysis is used as the gold standard to diagnose malabsorption syndrome. The Centers for Disease Control and Prevention recommend that stool samples submitted for enteric pathogen testing should also be tested for Shiga toxin (produced by Escherichia coli O157:H7 and other strains of E. coli).

TABLE 4.1 Stool Testing for Infections

Source of Stool Infection			Clinical Signs or Symptoms	Laboratory Test (Sequence or Follow-up)
Community Acquired from intermediate hosts, such as:			Diarrhea, bloody, purulent Steatorrhea Cramping, bloating, belching Small bowel obstruction, weight loss Generalized skin rash Huge swelling of legs, arms, or scrotum Huge lymphatic swelling Fever, chills, night sweats	Screen stool for ova and parasites Microscopic exam of stool for ova and parasites Stool culture for Clostridium difficile (some patients may require more than one assay) Eosinophilia in blood sample Exam for worms in stool or around anus Fecal smear for leukocytes and yeast
	Home—domestic pets, contaminated water Occupational
		Fishers—from snails and worms Meat cutters—from contaminated animals Healthcare workers— from patients Farm workers—from animals (cows, pigs), garden, flies, mosquitoes, fleas, other insects
	Recreational—backpacking, poor sanitation
		Travel—Third World— contaminated water supply Contact with fair animals
	Hookworm infection—not fecal or oral; passed via direct penetration of skin by larva in contaminated soil or in animal droppings
Nosocomial Acquired from institutions such as hospitals or nursing homes			Diarrhea Medication history of antibiotic use	Eosinophilia in blood sample Exam for worms in stool or around anus Microscopic exam of stool for ova and parasites Stool culture for C. difficile Fecal smear for leukocytes and yeast
Personal Contact with an infected host when patient is compromised (weakened immune system; i.e., HIV) or debilitated (such as a frail child or elderly patient)			Testing may occur following contact with infected host but before symptoms appear.	Screen stool for ova and parasites Microscopic exam of stool for ova and parasites Stool culture for C. difficile Toxin stool assay Acid-fast bacilli (AFB) in stool for tuberculosis Microsporidium

Patients and healthcare personnel may dislike collecting and examining stool samples; however, this natural aversion must be overcome in light of the value of a stool examination for diagnosing disturbances and diseases of the GI tract, the liver, and the pancreas.

STOOL SPECIMEN COLLECTION AND TRANSPORT PROCEDURES

• Collection and Transport Procedures for All Types of Stool Collection

Procedure

Observe standard precautions (see Appendix A) when procuring and handling specimens to avoid infectious pathogens (e.g., hepatitis A, Salmonella, and Shigella).
Collect stool sample in a dry, clean, urine-free container that has a properly fitting cover. If unsure of how to collect the specimen, contact the laboratory before collection is begun.
The fresh specimen should not be contaminated with urine or other bodily secretions such as menstrual blood. Stool can be collected from the diaper of an infant or incontinent adult. Samples can be collected from temporary ostomy bags.
Accurately label all stool specimens with the patient’s name, date, and tests ordered on the specimen. Keep the outside of the container free from contamination and immediately send the sealed container to the laboratory.
Place the specimen in a biohazard bag.
Post signs in bathrooms that say “DO NOT DISCARD STOOL” or “SAVE STOOL” to serve as reminders that stool sample collection is in progress.

Interfering Factors

Stool specimens from patients receiving tetracyclines, antidiarrheal medications, barium, bismuth, oil, iron, or magnesium may not yield accurate results.
Bismuth found in paper towels and toilet tissue interferes with accurate results.
Do not collect or retrieve stool from the toilet bowl or use a specimen that has been contaminated with urine, water, or toilet bowl cleaner. A clean, dry bedpan may be the best receptacle for defecation.
Inaccurate test results may result if the sample is not representative of the entire stool evacuation.
Lifestyle, personal habits, travel, home and work environments, and bathroom accessibility are some of the factors that may interfere with proper sample procurement.
Prompt transport of the specimen is necessary for accurate results. Trophozoites (protozoa in the early growth stage) in liquid stool disintegrate rapidly after defecation; therefore, the specimen needs to be examined 30 minutes from start of collection of specimen, not 30 minutes from end of collection. Semi-formed stool should be examined within 60 minutes after defecation. No trophozoites are seen in formed stool.

Interventions

Pretest Patient Care

Explain purpose of test, procedure for stool collection, and interfering factors using a culturally competent and culturally sensitive approach. Because the specimen cannot be obtained on demand, it is important to provide detailed instructions before the test so that the specimen is collected when the opportunity presents itself. Provide written instructions if necessary.
Provide proper containers and other collection supplies. Instruct the patient to defecate in a largemouthed plastic container, bag, or clean bedpan. Provide for and respect the patient’s privacy.
Instruct the patient not to urinate into the collecting container or bedpan.
Do not place toilet paper in the container or bedpan because it interferes with testing.
If the patient has diarrhea, a large plastic bag attached by adhesive tape to the toilet seat may be helpful in the collection process. After defecation, the bag can be placed into a container.
Specimens for most tests can be produced by a warm saline enema or Fleet Phospho-Soda enema.
Tests for both ova and parasites and cultures for enteric pathogens may be ordered together. In this case, the specimen should be divided into two samples, with one portion refrigerated for culture testing and one portion kept at room temperature for ova and parasite testing. Commercial collection kits are available that require the stool to be divided and placed into separate vials for better recovery of ova and parasites and enteric pathogens. (See Chapter 7, Microbiologic Studies.)
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

Provide patient privacy and the opportunity to cleanse perineal area and hands. Assist as necessary.
Review test results; report and record findings. Modify the nursing care plan as needed.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Collection and Transport of Random Specimens

Observe the Collection and Transport Procedures for All Types of Stool Collection on pages 276 through 277 of this chapter.
Collect the entire stool sample and transfer it to a clean container using a clean tongue blade or similar object. A sample 2.5-cm (1-inch) long or 64.7 mg (1 oz) of liquid stool may be sufficient for some tests.
For best results, cover specimens and deliver to the laboratory immediately after collection. Depending on the examination to be performed, the specimen should be either refrigerated or kept warm. Contact the laboratory for detailed instructions concerning the temperature of stool specimen before collection is begun to avoid delay once the specimen is obtained.

• Collection and Transport of Specimens for Ova and Parasites

Observe the Collection and Transport Procedures for All Types of Stool Collection on pages 276 through 277 of this chapter.
Warm stools are best for detection of ova and parasites. Do not refrigerate specimens for ova and parasites.
Special vials that contain 10% formalin and polyvinyl alcohol (PVA) fixative may be used for collecting stool samples to test for ova and parasites.
Because of the life cycle of parasites, three separate random stool specimens for analysis are recommended.

• Collection and Transport of Specimens for Enteric Pathogens

Observe the Collection and Transport Procedures for All Types of Stool Collection on pages 276 through 277 of this chapter.
Some coliform bacilli produce antibiotic substances that destroy enteric pathogens. Refrigerate the specimen immediately to prevent this from happening in the sample.
Samples that are diarrheal rather than formed stool are usually still adequate to give accurate results.
A freshly passed stool is the specimen of choice.
Collect stool specimens before antibiotic therapy is initiated and as early in the course of the disease as possible.
If mucus or blood is present, it should be included with the specimen because pathogens are more likely to be found in these substances. If only a small amount of stool is available, a walnut-sized specimen is usually adequate.
Keep the outside of the collection container free from contamination and immediately send the sealed container to the laboratory.
For best preservation and transport of specimens suspected of containing pathogens, a Cary-Blair solution (which contains sodium thioglycolate, disodium phosphate, sodium chloride, agar, and distilled water) vial with indicator should be used.

• Collection and Transport of 24-, 48-, 72-, and 96-Hour Stool Specimens

This method is used to test for fat, porphyrins, urobilinogen, nitrogen, and electrolytes.

Procedure for Submitting Individual Specimens

Observe the Collection and Transport Procedures for All Types of Stool Collection on pages 276 through 277 of this chapter.
Collect all stool specimens for 1 to 3 days. The entire stool should be collected. Some procedures may require 4 days.
Label specimens with day of test (e.g., Day 1, Day 2, Day 3, Day 4), time of day collected, patient’s name, and test(s) ordered. It is important to disclose the number of days collected because this information is needed for calculations.
Submit individual specimens to the laboratory as soon as they are collected.

Procedure for Submitting Total Specimens

Observe the Collection and Transport Procedures for All Types of Stool Collection on pages 276 through 277 of this chapter.
Obtain a 1-gallon container from the laboratory (a 1-gallon paint tin or covered plastic pail is preferred).
Save all stool and place in the container. Keep refrigerated or in a container with canned ice and replace ice as needed.
Label the specimen with the patient’s name, dates and times of collections, duration of collection time, and test(s) ordered.
Transfer the properly labeled container to the laboratory at the end of the collection period.

STOOL STUDIES

• Stool Consistency, Shape, Form, Amount, and Odor

Inspection of the feces is an important diagnostic tool. The quantity, form, consistency, and color of the stool should be noted. Normally, stool reflects the shape and caliber of the colonic lumen as well as the colonic motility. The normal consistency is somewhat plastic and neither fluid, mushy, nor hard. Consistency can also be described as formed, soft, mushy, frothy, or watery. When diarrhea is present, the stool is watery. Large amounts of mushy, frothy, foul-smelling stool are characteristic of steatorrhea (excess fat in the feces). Constipation is associated with hard, spherical masses of stool.

Feces have a characteristic odor that varies with diet and the pH of the stool. The odor of normal stool is caused by indole (produced in intestine by breakdown of tryptophan) and skatole (formed from decomposition of protein) formed by bacterial fermentation and putrefaction.

Normal Findings

100 to 200 g/24 hours or 100 to 200 g/day
Characteristic odor present; plastic, soft, formed; soft and bulky on a high-fiber diet; small and dry on a high-protein diet; seeds and small amounts of vegetable fiber present (as opposed to muscle fiber) (Table 4.2)

Clinical Implications

Stool consistency alterations
- Diarrhea due to the following:
  - Infection—Salmonella, Shigella, Yersinia, HIV enteropathy, Campylobacter
  - Inflammatory disorder—Crohn’s disease, ulcerative colitis
  - Steatorrhea—celiac disease
  - Carbohydrate malabsorption—lactose or sucrose deficiency
  - Endocrine abnormalities—diabetes mellitus, hyperthyroidism or hypothyroidism, adrenal insufficiency
  - Hormone-producing tumors—Zollinger-Ellison syndrome (pancreatic gastrin-secreting tumor leading to increased acid activity in the stomach), gastrinoma, medullary thyroid carcinoma, villous adenoma
  - Colon carcinoma
  - Infiltration of lesions due to lymphoma, scleroderma of bowel
  - Drugs, antibiotics, cardiac medications, chemotherapy
  - Osmotically active dietary items—sorbitol, psyllium fiber, caffeine, ethanol
  - GI surgery—gastrectomy, stomach stapling, intestinal resection
  - Factitious—self-induced laxative abuse associated with psychiatric disorders
- “Pasty” stool associated with high-fat content can be caused by the following:
  - Common bile duct obstruction
  - Celiac disease
  - Cystic fibrosis—greasy “butter” stool appearance due to pancreatic involvement
- Bulky or frothy stool is usually due to steatorrhea and celiac disease.
Stool size or shape alterations indicate altered motility or colon wall abnormalities.
- A narrow, ribbon-like stool suggests the possibility of spastic bowel, rectal narrowing or stricture, decreased elasticity, or a partial obstruction.
- Excessively hard stools are usually due to increased fluid absorption because of prolonged contact of luminal contents with colon mucosa during delayed transmit time through the colon.
- A large-circumference stool indicates dilation of the viscus.
- Small, round, hard stools (i.e., scybala) accompany habitual, moderate constipation.
- Severe fecal retention can produce huge, firm, impacted stool masses with a small amount of liquid stool as overflow. These must be removed manually, occasionally under light anesthesia.
Fecal odor should be assessed whenever a stool specimen is collected.
- A foul odor is caused by dehydration of undigested protein and is produced by excessive carbohydrate ingestion.
- A sickly sweet odor is produced by volatile fatty acids and undigested lactose.
Mucus in stool occurs in constipation, malignancy, and colitis.

TABLE 4.2 Normal Values in Stool Analysis

Macroscopic Examination	Normal Value
Amount	100-200 g/24 hr (100-200 g/d)
Color	Brown
Odor	Varies with pH of stool and depends on bacterial fermentation and putrefaction
Consistency	Plastic; not unusual to see fiber, vegetable skins, and seeds; soft and bulky in high-vegetable diet; small and dry in high-meat diet
Size and shape	Formed
Gross blood	None
Mucus	None
Pus	None
Parasites	None
Microscopic Examination	Normal Value
Fat	Colorless, neutral fat (18%) and fatty acid crystals and soaps
Undigested food, meat fibers, starch, trypsin	None to small amount
Eggs and segments of parasites	None
Bacteria and viruses	None
Yeasts	None
Leukocytes	None
Chemical Examination	Normal Values
Water	Up to 75% (0.75)
pH	Neutral to weakly alkaline (pH 7.0-7.5)
Occult blood	Negative
Urobilinogen	50-300 mg/24 hr (50-300 mg/d)
Porphyrins	Coproporphyrins: 400-1200 μg/24 hr (611-1832 nmol/d) Uroporphyrins: 10-40 μg/24 hr (12-48 nmol/d)
Nitrogen	<2.5 g/24 hr (<178 mmol/d)
Apt test for swallowed blood	Negative in adults; positive in newborns
Trypsin	20-95 U/g
Osmolality, used with stool	200-250 mOsm
Sodium	5.8-9.8 mEq/24 hr (5.8-9.8 mmol/d)
Chloride	2.5-3.9 mEq/24 hr (2.5-3.9 mmol/d)
Potassium	15.7-20.7 mEq/24 hr (15.7-20.7 mmol/d)
Lipids (fatty acids)	0-6 g/24 hr (0-21 mmol/d)
Carbohydrates (as reducing substances)	<0.25 g/dL (<2.5 g/L)
Note: Normal values for electrolytes vary greatly; check with your reference laboratory.

Interventions

Pretest Patient Care

Explain purpose of test and procedure for stool collection. Instruct the patient to refrigerate the specimen. Provide clean, dry, leakproof collection container.
Advise the patient to avoid barium procedures and laxatives for 1 week before stool specimen collection.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Assessment of Diarrhea and Constipation

When performing a workup for the differential diagnosis of diarrhea or constipation, a patient history is most important. The following factors should be charted:
- An estimate of volume and frequency of fecal output
- Stool consistency and presence of blood, pus, mucus, oiliness, or bad odor in specimen; evaluate through direct observation when possible
- Decrease or increase in frequency of defecation
- Sensations of rectal fullness with incomplete stool evacuation
- Painful defecation
Assess dietary habits and food allergies.
Assess emotional state of patient—psychological stress may be major cause of altered bowel habits.
Assess for signs of laxative abuse.

Posttest Patient Care

Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings. If patient has watery diarrhea, note history of contact with affected family members, travel to a developing country, vacation or resort travel to areas at high risk for travelers’ diarrhea, community and municipal water supply, or contact with farm animals. Explain that additional testing (e.g., colonoscopy) may be necessary.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

• Stool Color

The brown color of normal stool is probably due to stercobilin (end product of heme catabolism), a bile pigment derivative, which results from the action of reducing bacteria in bilirubin and other undetermined factors.

The first indication of GI disturbances is often a change in the normal brown color of the feces. A change in color can provide information about pathologic conditions, organic dysfunction, or intake of drugs. Color abnormalities may aid the healthcare provider in selection of appropriate diagnostic chemical and microbiologic stool tests.

Normal Findings

Brown

Clinical Implications

The color of feces changes in some disease states as follows:

Yellow, yellow-green, or green: severe diarrhea
Black, with a tarry consistency: usually the result of bleeding in the upper GI tract (> 100 mL blood)
Maroon, red, or pink: possibly the result of bleeding of the lower GI tract from tumors, hemorrhoids, fissures, or an inflammatory process

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Tags: Fischbach's A Manual of Laboratory and Diagnostic Tests

Sep 25, 2018 | Posted by drzezo in PATHOLOGY & LABORATORY MEDICINE | Comments Off

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