Body Fluids- Fecal Analysis

Fecal analysis

Laboratory examination of stool for digestive, absorptive, inflammatory, and bleeding disorders

Primary indications for fecal examination

GI bleeding, diarrhea, malabsorption, infection, liver and biliary disease

Routine fecal examination components

Macroscopic, microscopic, and chemical analysis

Fecal formation

Results from digestion and absorption in the GI tract

Daily fluid input to GI tract

Approximately 9,000 milliliters

Fluid reaching large intestine

Approximately 500 to 1,500 milliliters

Normal fecal water excretion

Approximately 150 milliliters per day

Diarrhea

Passage of abnormally frequent or liquid stools

Secretory diarrhea

Caused by impaired water reabsorption due to infection, drugs, or hormones

Osmotic diarrhea

Caused by nonabsorbed solutes retaining water in intestine

Osmotic diarrhea mechanism

Incomplete digestion or absorption of nutrients

Inflammatory diarrhea

Associated with mucosal damage and WBCs in stool

Random stool specimen

Used for qualitative testing

Timed stool specimen

Used for quantitative testing such as fecal fat

Three day stool collection

Required for quantitative fecal fat testing

Stool specimen contamination

Urine, toilet water, tissue paper, barium, or laxatives

Specimen handling precaution

Avoid refrigeration unless specified

Normal stool color

Brown due to oxidation of urobilinogen to urobilin

Pale or clay colored stool

Indicates bile duct obstruction

Black stool

Indicates upper GI bleeding or iron ingestion

Bright red stool

Indicates lower GI bleeding or hemorrhoids

Green stool

Seen with antibiotics or rapid transit

Yellow stool

Seen in malabsorption and steatorrhea

Normal stool appearance

Soft, formed, and homogeneous

Watery stool

Associated with diarrhea

Ribbon like stool

Suggests intestinal obstruction

Hard stool

Seen in constipation

Bulky frothy stool

Seen in pancreatic or biliary disorders

Steatorrhea

Excess fat in stool causing greasy appearance

Mucus in stool

Indicates inflammation or colitis

Fecal leukocytes

White blood cells present in stool

Significance of fecal leukocytes

Indicates inflammatory diarrhea

Threshold for fecal leukocytes

Greater than 3 WBCs per high power field

Diseases with fecal leukocytes

Ulcerative colitis and bacterial dysentery

Bacterial causes of fecal leukocytes

Shigella, Salmonella, Campylobacter, Yersinia, E coli

Absence of fecal leukocytes

Seen in toxin mediated diarrhea

Toxin producing organisms

Staphylococcus aureus and Vibrio species

Muscle fibers in stool

Indicator of protein digestion

Significant muscle fibers

Greater than 10 fibers per slide

Cause of muscle fibers in stool

cause- Pancreatic insufficiency

Associated conditions muscle fibers

Cystic fibrosis and chronic pancreatitis

Occult blood

Hidden blood in stool not visible macroscopically

Principle of occult blood testing

Peroxidase activity of hemoglobin oxidizes indicator

Guaiac occult blood test

Most commonly used fecal occult blood test

Positive occult blood test

Blue color change

False positive occult blood

Red meat, horseradish, turnips, iron

False negative occult blood

Vitamin C ingestion

Upper GI bleeding occult blood

May be false negative due to hemoglobin degradation

Melena

Black tarry stool from digested blood

Apt test

Differentiates fetal from maternal blood in neonates

Indication for Apt test

Bloody stool or vomitus in newborns

Principle of Apt test

Fetal hemoglobin is resistant to alkali

Positive Apt test

Pink color indicating fetal hemoglobin

Negative Apt test

Yellow color indicating maternal hemoglobin

Fecal fat

Measurement of fat excretion in stool

Steatorrhea diagnosis

Increased fecal fat

Qualitative fecal fat test

Sudan III, Sudan IV, or Oil Red O stain

Sudan stain positive result

Red orange fat globules

Limitations of qualitative fecal fat

Does not detect phospholipids or cholesterol esters

Quantitative fecal fat test

Confirmatory test for steatorrhea

Van de Kamer method

Titration of fecal fatty acids

Normal quantitative fecal fat

1 to 6 grams per day

Abnormal fecal fat excretion

Greater than 7 grams per day

Coefficient of fat retention

Percentage of dietary fat absorbed

Normal coefficient of fat retention

Greater than 95 percent

Maldigestion

Impaired breakdown of nutrients due to enzyme deficiency

Malabsorption

Impaired intestinal absorption of nutrients

Maldigestion cause

maldig- Pancreatic insufficiency

Malabsorption cause

Intestinal mucosal damage

Fecal enzymes

Used to evaluate pancreatic function

Decreased fecal elastase

Indicates pancreatic insufficiency

Proteolytic enzymes in feces

Trypsin, chymotrypsin, elastase

Carbohydrate malabsorption

Incomplete absorption of carbohydrates

Effect of carbohydrate malabsorption

Osmotic diarrhea

Stool pH in carbohydrate malabsorption

Decreased

Copper reduction test

CRT- Detects reducing sugars in stool

Clinitest

Common copper reduction test

Positive copper reduction test

Indicates presence of reducing sugars

Confirmatory test after positive Clinitest

D xylose test

Lactose intolerance

Inability to digest lactose due to lactase deficiency

Primary lactose intolerance

Genetic loss of lactase activity

Secondary lactose intolerance

Acquired due to intestinal injury or infection

Differentiation of malabsorption vs maldigestion

Based on enzyme activity and absorption testing

Cells in diarrhea inflammatory

WBCs present

Cells in diarrhea non inflammatory

No WBCs present

Correlation of fecal findings and disease

Used to diagnose GI bleeding, infection, and malabsorption

Steatorrhea with pancreatic enzymes low

Suggests pancreatic insufficiency

Occult blood positive with anemia

Suggests GI malignancy

Fecal leukocytes with bloody diarrhea

Suggests invasive bacterial infection