Stool Sample Analysis Quiz

Fecal Body Fluid Examination

• Fecal specimens are examined to diagnose gastrointestinal disorders, infections, and malabsorption syndromes.
• Learning objectives include identifying fecal components, performing gross and microscopic examinations, and understanding chemical testing procedures.

Introduction

• Routine fecal examinations involve macroscopic, microscopic, and chemical analyses.
• These analyses are used to detect gastrointestinal (GI) bleeding, liver and biliary duct disorders, maldigestion/malabsorption syndromes, pancreatic diseases, inflammation, causes of diarrhea and steatorrhea.
• Detection of pathogenic bacteria, viruses, and parasites is also important.
• Normal stool contains bacteria, cellulose, undigested foodstuffs, GI secretions, bile pigments, cells from the intestinal walls, electrolytes, and water.
• Approximately 100 to 200 grams of feces are excreted per 24-hour period.
• The large intestine absorbs approximately 3,000 mL of water.
• Diarrhea occurs when the amount of water reaching the large intestine exceeds its absorption capacity.
• Constipation allows the large intestine more time to absorb water from the fecal material, resulting in small, hard stools.

Specimen Collection

• Collecting a fecal specimen (stool) can be challenging for patients.
• Detailed instructions and appropriate containers, tailored to the specific tests and required stool volume, should be provided.
• Dietary restrictions may be needed before collecting specimens for certain tests.
• Clean containers, such as bedpans or disposable containers, should be used for collection, and the specimen transferred to a laboratory container.
• Specimens must not be contaminated with urine, disinfectants, or deodorizers as these can interfere with chemical testing.
• Containers for ova and parasite testing must not be used for other analyses.
• Random specimens for blood, leukocytes, muscle fibers, and fat analysis are usually collected in plastic or glass screw-top containers are similar to those for urine collection.

Gross Examination

• Appearance: Normal stool is brown, soft, and well-formed. Abnormal appearances include black/tarry (GI bleeding), pale/clay-colored (biliary obstruction), bloody (lower GI bleeding) or greenish (bile salt presence).
• Consistency: Hard stools suggest constipation, while watery stools suggest diarrhea or malabsorption.
• Odor: Foul-smelling stool suggests infection or malabsorption.

Macroscopic Screening

• Changes in stool color and consistency can be the first signs of GI disturbances.
• Ingestion of highly pigmented foods or medications can also cause variations in stool color, requiring differentiation between normal and pathological causes.

Color

• Stool color results from intestinal oxidation of stercobilinogen to urobilin
• Conjugated bilirubin, resulting from hemoglobin breakdown, is converted to urobilinogen by intestinal bacteria and then to stercobilinogen.
• Pale stool (acholic stool) may indicate bile duct blockage.
• Blood in stool can range in color from bright red to dark red or black, depending on the bleeding site. Black, tarry stools typically from upper GI bleeding.
• Lower GI bleeding results in red or bloody stool.
• Green stool may be caused by oral antibiotics or increased intake of green vegetables or food coloring.

Appearance

• Variations in stool consistency, including watery diarrhea, small hard stools (constipation), and ribbon-like stools (obstruction), may be observed.
• Pale, bulky, frothy, and foul-smelling stool may indicate biliary obstruction or steatorrhea.
• Greasy stool that floats usually indicates steatorrhea.
• Mucus-coated stool suggests inflammation or irritation, possibly due to colitis, Crohn's disease, colon tumors, or excessive straining during elimination. Blood-streaked mucus may signify damage to the intestinal walls, potentially due to bacterial or amebic dysentery or malignancy.

Morphological Examination

• Parasite Identification: Protozoa (e.g., Entamoeba histolytica, Giardia lamblia) and helminths (e.g., Ascaris lumbricoides, hookworms) are identified.
• Cellular Elements: Epithelial cells may indicate tissue damage; yeast cells suggest fungal infections. Undigested materials like food debris or gum are also identified.

Cell Counts

• Microscopic Examination: Red blood cells (RBCs) may indicate GI tract bleeding; white blood cells (WBCs) may suggest infection or inflammation; parasites and eggs suggest parasitic infections; and fat globules suggest malabsorption or pancreatic insufficiency.

Microscopic Examination of Feces

• Microscopic screening identifies leukocytes (often neutrophils) indicative of microbial diarrhea, undigested muscle fibers, and fats in cases of steatorrhea
• It's used as a preliminary test for invasive bacteria like Salmonella, Shigella, Campylobacter, Yersinia, and enteroinvasive E. coli.

Microscopic Examination of Feces: Bacteria, Viruses, Parasites

• Bacteria, viruses, and parasites that cause diarrhea often do not cause visible fecal leukocytes.
• The presence or absence of fecal neutrophils helps diagnose before cultures.
• Specimens can be examined as wet preparations stained with methylene blue or as dried smears stained with Wright's or Gram stains (methylene blue is faster, but Gram staining is often easier to interpret). Permanence slides are also provided.
• Gram staining aids in identifying gram-positive and gram-negative bacteria, aiding initial treatment.
• Three neutrophils per high-power field suggests invasive condition. Neutrophils in oil immersion have approximately 70% sensitivity for invasive bacteria.

Microscopic Examination of Feces: Muscle Fibers

• Microscopic examination of the stool for undigested striated muscle fibers can aid in the diagnosis and monitoring of pancreatic insufficiency, such as in cystic fibrosis cases.
• Preparation includes emulsifying a small amount of stool in 10% alcoholic eosin, which highlights muscle fiber striations. The slide is examined for exactly 5 minutes, and red-stained fibers with well-preserved striations are counted.

Microscopic Examination of Feces: Fecal Fats

• Specimens from suspected steatorrhea cases can be microscopically screened for excess fat (steatorrhea).
• Fat staining with Sudan III, Sudan IV, or oil red O is used to identify fat globules, with Sudan III used most commonly.

Microorganisms in Stool

-Bacteria: Escherichia coli (E. coli) causes diarrhea, especially in children, and some strains lead to hemolytic uremic syndrome. Salmonella causes diarrhea, fever, and abdominal cramps. Shigella causes dysentery with bloody diarrhea, fever, and abdominal cramps. Campylobacter often causes bacterial gastroenteritis with diarrhea, fever, and abdominal pain. Clostridium difficile can cause antibiotic-associated diarrhea and colitis.

• Yeast: Candida spp., can be part of normal flora, but in immunocompromised individuals, they lead to infection (candidiasis) and diarrhea.
• Protozoa: Entamoeba histolytica causes amoebiasis that leads to abdominal pain, dysentery, and potential liver abscess. Morphology: Cysts are round with 4 nuclei; trophozoites are motile and may engulf red blood cells. Giardia lamblia: Causes giardiasis; symptoms include diarrhea, bloating, and malabsorption. Morphology: Pear shaped protozoans with 2 nuclei and 4 flagella. Balantidium coli: Large, ciliated protozoan with a kidney-shaped macronucleus. Causes balantidiasis, leading to dysentery.
• Blastocystis hominis: A common intestinal parasite frequently found in stool samples.
• Helminths: Ascaris lumbricoides (roundworm) causes ascariasis, potentially causing intestinal obstruction, malnutrition, and respiratory issues during migration. Trichuris trichiura (whipworm) causes trichuriasis, often resulting in abdominal pain, diarrhea, and rectal prolapse. Enterobius vermicularis (pinworm) causes enterobiasis; signs include itching around the anus, particularly at night. Strongyloides stercoralis (a helminth) can cause persistent diarrhea, abdominal pain, and, in severe cases, disseminated infection in immunocompromised individuals; Rhabditiform larvae are identified.
• Tapeworms: Taenia spp. causes taeniasis, leading to abdominal pain, weight loss, and digestive issues. Eggs are round and contain a hexacanth embryo.

Schistosoma spp. (Blood Flukes)

• Oval eggs with characteristic lateral spine.
• Causes schistosomiasis, with symptoms ranging from mild to severe abdominal pain, blood in stools, and liver enlargement.

Chemical Testing of Feces

• Occult Blood: Detects hidden blood. Upper GI bleeding often results in black, tarry stool—lower GI bleeding results in visibly bloody stool. Fecal occult blood testing (FOBT) is important because bleeding (excess of 2.5 mL/150 g stool) may be present without visible signs, but it is significant from a pathological standpoint.
• Guaiac-Based Fecal Occult Blood Tests (gFOBT): Used to detect occult blood, based on hemoglobin's peroxidase activity.
  • The procedure involves applying material from different stool sections to filter paper areas on a slide, with positive and negative controls, to avoid external contamination. Collect on 3 consecutive days.
  • Hydrogen peroxide is added to the back of the slide containing the sample. Bluing with the guaiac reagent indicates a positive reaction.
• Other Chemical Tests: Additional chemical tests include pH measurements (normal range = 6.0-7.5; acidic in diarrhea), reducing substances (detect carbohydrate malabsorption), fat staining (using Sudan III or Oil Red O to detect fat globules), and enzyme testing (measuring trypsin and chymotrypsin for pancreatic function).

Quality Control and Sample Handling

• Sample Collection and Transport: Use sterile containers; avoid urine or toilet water contamination; transport specimens promptly.
• Quality Assurance: Standardized reporting formats and follow lab safety and handling protocols are essential.

Summary

• Gross Examination: Initial visual assessment of stool characteristics (color, consistency, and odor).
• Microscopic Examination: Identification of cells, parasites, pathogens.
• Chemical Testing: Confirmation of blood, fats, and enzymes in stool samples.

Questions and Discussion

• Real-life case scenarios and diagnostic challenges.
• Open discussion on interpretation techniques and troubleshooting.

Test your knowledge on stool sample analysis with this quiz. It covers various aspects such as pH levels, examination methods, and indicators of different conditions. Perfect for students in health science or those studying laboratory techniques.