fecal analysis

7/29/2019 Fecal Analysis

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FECAL ANALYSIS

ROUTINE FECAL EXAMINATION

macroscopic, microscopic and chemical analysis of feces for the early detection of:o gastrointestinal (GI) bleedingo liver and biliary duct disorderso maldigestion/malabsorption syndromeso inflammation

o causes of diarrhea and steatorrheao detection of pathogenic bacteria and

parasites

PHYSIOLOGY

Normal fecal specimen contains:

o bacteria (many of which make up thenormal flora of the intestines

o celluloseo other undigested foodstuffso GI secretions

o bile pigmentso cells from the intestinal wallso electrolyteso water

BACTERIAL METABOLISM

produces the strong odor associated with feces and intestinal gas (flatus)CARBOHYDRATES

especially oligosaccharides

resistant to digestion pass through the upper intestine unchanged but are metabolized by bacteria in the lower intestine, producing large

amounts of flatus

excessive gas production: LACTOSE-INTOLERANT INDIVIDUALS when the intestinal bacteria metabolize the lactose fromconsumed milk or lactose-containing substances

ALIMENTARY TRACT

where digestion of ingested proteins, carbohydrates and fats take placeSMALL INTESTINE

primary site for the final breakdown and reabsorption of these compoundsDIGESTIVE ENZYMES SECRETED INTO THE SMALL INTESTINE BY THE PANCREAS

trypsin chymotrypsin amino peptidase lipase

BILE SALTS

provided by the liver aid in the digestion of fats

* A deficiency in any of these substances causes the inability to digest, and, therefore, to reabsorb certain foods


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EXCESS UNDIGESTED OR REABSORBED MATERIAL

appear in feces patient exhibits symptoms of maldigestion and malabsorption

INGESTED FLUID, SALIVA, GASTRIC, LIVER, PANCREATIC AND INTESTINAL SECRETIONS

DIGESTIVE TRACT

LARGE INTESTINE

FECES

WATER AND ELECTROLYTES

readily absorbed in both intestines fecal electrolyte content similar to plasma

LARGE INTESTINE

can absorb approximately 3000 mL of waterDIARRHEA

occurs when amount of water reaching the large intestine exceeds 3000 mL water is excreted with the solid fecal material

CONSTIPATION

provides time for additional water to be reabsorbed from the fecal material small, hard stools

DIARRHEA

DIARRHEA

increase in daily stool weight above 200 g increased liquidity frequency: more than 3X/day can be classified based on:a. Duration of the illness

o ACUTE: less than 4 weekso CHRONIC: more than 4 weeks

b. MechanismOsmotic gap = 290[2 (fecal Na+ + fecal K+)

Osmotic diarrhea = >50 mOsm/kg, negligible electrolytes

Secretory diarrhea =


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MECHANISM ACTION CAUSATIVE AGENTS OTHER CAUSES

Secretory

Increase in

secretion of

water and

electrolytes

which override

the

reabsorptive

ability of the

large intestines

E. coli Clostridium V. cholerae Salmonella Shigella Staphylococcus Campylobacter Protozoa Cryptosporidium

Drugs Stimulant laxatives Hormones Inflammatory bowel disease

o Crohn diseaseo Ulcerative colitiso Lymphocytic colitiso Diventiculitis

Endocrine disorderso Hyperthyroidismo Zollinger-Ellison syndromeo Vipoma

Neoplasms Collagen vascular disease

Osmotic

Incomplete

breakdown or

reabsorption of

food presents

increased

fecal material

to the large

intestine,

resulting in theretention of

water and

electrolytes in

the large

intestine

Entamoeba histolytica

Disaccharidase deficiency (lactoseintolerance)

Malabsorption (Celiac sprue) Poorly absorbed sugars (lactose,

sorbitol, mannitol)

Laxatives Magnesium-containing antacids Antibiotic administration

Altered

Motility

Conditions of

enhanced

motility

(hypermotility)

or slow motility

(constipation)

Vagotomy Diabetic neuropathy Complication of menstruation Hyperthyroidism

RRITABLE BOWEL SYNDROME (IBS) both hypermotility and constipation are seen a functional disorder in which the nerves and muscles of the bowel are extra-sensitive, causing:

o crampingo bloatingo flatus

o diarrheao constipation

triggered by:o foodo chemicalso emotional stresso exercise

RAPID (ACCELERATED) GASTRIC EMPTYING (RGE) DUMPING SYNDROME hypermotility of the stomach shortened gastric emptying half-time, causing the small intestines to fill too quickly with undigested food from the stoma hallmark of Early Dumping Syndrome (EDS) healthy individuals: gastric emptying half-time range of 35-100 minutes (varies with age and gender) RGE: less than 35 minutes caused by disturbances in the gastric reservoir or in the transporting function normal gastric emptying is controlled by the FUNDIC TONE, DUODENAL FEEDBACK and GI HORMONES


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START SYMPTOMS COMPLICATION CAUSES

Early Dumping

10-30 minutes

following meal

ingestion

Nausea Vomiting Bloating Cramping Diarrhea Diziness Fatigue

Hypoglycemia

Gastrectomy Gastric bypass

surgery

Postvagotomystatus

Zollinger-Ellisonsyndrome

Duodenal ulcedisease

Diabetes mellitLate Dumping2-3 hours after a

meal

Weakness Sweating Dizziness

STEATORRHEA

increase in stool fat that exceeds 6 g/day due to absence of bile salts that assist pancreatic lipase in the breakdown asubsequent reabsorption of triglycerides

detection is useful for the diagnosis of pancreatic insufficiency and small boweled disorders that cause malabsorption disease association:

o Cystic fibrosiso Chronic pancreatitiso Carcinoma

Steatorrhea

Maldigestion and Malabsorption

D-Xylose Test

Malabsorption

D-XYLOSE a sugar that does not need to be digested but does need to be absorbed to be present in urine if low: Malabsorption if normal: Pancreatitis

MALABSORPTION CAUSES

o Bacterial overgrowtho Intestinal resectiono Celiac diseaseo Tropical sprueo Lymphoma

o Whipple diseaseo Giardia lamblia infestationo Crohn diseaseo Intestinal ischemia

c. Severityd. Stool characteristics

may be present

9000 mL/day

urine D-Xylose is low


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SPECIMEN COLLECTION

1. Collect specimen in a clean container, such as a bedpan or disposable container.2. Transfer specimen to laboratory container.

Precaution: SPECIMEN MUST NOT BE CONTAMINATED WITH URINE OR TOILET WATER, which may contain disinfectants.

KITS FOR OCCULT BLOOD

contain paper that can be floated in toilet bowl to collect the specimenRANDOM SPECIMENS

for qualitative testing for blood microscopic examination for leukocytes, muscle fibers and fecal fats container: PLASTIC OR GLASS CONTAINERS WITH SCREW-CAPPED TOPS

TIMED SPECIMENS

for quantitative testing for fecal fats most representative sample: 3-DAY COLLECTION

o due to variability of bowel habits and transit time required for food to pass through the digestive tract container: PAINT CANS to accommodate specimen quantity and facilitate emulsification prior to testing

MACROSCOPIC SCREENING

first indication of GI disturbances:o changes in brown coloro formed consistency

COLOR

BROWNPALE YELLOW, WHITE,

GRAYBLACK, TARRY RED GREEN

Normal:

Stercobilinogen

to Urobilin

Blockage ofthe bile duct

Diagnosticprocedures

that use

barium sulfate

Esopaghus bleeding Stomach bleeding Duodenal bleeding

o all of thesetake 3 days to

appear in

stool

Iron ingestion Charcoal ingestion Bismuth ingestion

(antacids)

Lower GIbleeding

Medications Food, especially

Beets

Oralantibiotic

(bilirubin t

biliverdin) Ingestion

increased

amounts o

green

vegetable

Foodcoloring

APPEARANCE

WATERY

CONSISTENCY SMALL, HARD STOOLS

SLENDER,

RIBBON-

LIKE

STOOLS

BULKY, FROTHY, FOUL

ODOR, GREASY, MAYFLOAT

MUCUS-COATED

STOOLS

BLOOD-STREAK

MUCUS-streak

Diarrhea ConstipationIntestinal

constriction

Biliary obstruction

Steatorrhea

Pancreatic disorders

Intestinal

inflammation or

irritation

Bacterial or ame

dysentery


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MICROSCOPIC EXAMINATION OF FECES

FECAL LEUKOCYTES

primarily neutrophils seen in infections that affect intestinal mucosa such as ULCERATIVE COLITIS and BACTERIAL DYSENTERY PRELIMINARY TEST to determine causative agent

INVASIVE BACTERIAL PATHOGENS

CAUSE THE APPEARANCE OF FECAL LEUKOCYTES

TOXIN-PRODUCING BACTERIA

USUALLY DO NOT CAUSE THE APPEARANCE OF FECAL

LEUKOCYTES

Salmonella Shigella Campylobacter Yersinia Enteroinvasive E. coli

Staphylococcus aureus Vibrio spp.

STAIN ADVANTAGES DISADVANTAGES

Wet preparation Methylene blue Faster More difficult to interp

Dried smear Wrights Grams

Provide permanentslides

Observation of Gram(+) and Gram (-)

bacteria

All slide preparations: FRESH SPECIMEN 3 neutrophils/hpf: INVASIVE CONDITION OIO: finding of neutrophils has approximately 70% sensitivity for the presence of invasive bacteria Lactoferrin Latex Agglutination Test

o detects fecal leukocytes and remains sensitive in refrigerated and frozen specimenso LACTOFERRIN: granulocyte secondary granule

MUSCLE FIBERS

Indicative of pancreatic insufficiency, such as CYSTIC FIBROSIS, BILIARY OBSTRUCTION and GASTROCOLIC FISTULAS emulsify a small amount of stool in 10% alcoholic eosin, which enhances the muscle fiber striations slide is examined for 5 minutes number of RED-STAINED FIBERS WITH WELL-PRESERVED STRIATIONS are counted UNDIGESTED FIBERS: visible striations running both vertically and horizontally; ONLY ONES COUNTED PARTIALLY DIGESTED FIBERS: striations in only one direction presence of MORE THAN 10 UNDIGESTED FIBERS are considered increased representative sample: RED MEAT IN DIET PRIOR TO COLLECTION; examined within 24 hours

QUALITATIVE FECAL FATS

specimens suspected of steatorrhea: MICROSCOPIC EXAMINATION FOR EXCESS FECAL FATo monitoring patients undergoing treatment for malabsorption disorders

stains: Sudan III (routine), Sudan IV, Oil Red O NEUTRAL FATS (TRIGLYCERIDES)

o stained by Sudan III as large orange-red droplets often located near the edge of cover slipo >60 droplets/hpf: steatorrheao SPLIT FAT STAINING

total fat content; breakdown of neutral fats by bacterial lipase and hydrolysis of neutral fats may loweneutral fat count

determine whether maldigestion or malabsorption causes steatorrhea SOAPS and FATTY ACIDS

o do not stain with Sudan IIIo second slide mixed with acetic acid and heated

stained droplets: free fatty acids, fatty acids from soap and neutral fat hydrolysiso Normal: 100 small droplets,


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o Slightly elevated: 100 small droplets, 1-8mo Increased: 100 droplets measuring 6-75 m

CHOLESTEROLo stained by Sudan III after heatingo forms crystals upon cooling

CHEMICAL TESTING OF FECES

OCCULT BLOOD

Fecal Occult Blood Test (FOBT) detection of hidden blood most frequently performed fecal analysis bleeding >2.5 mL/150 g of stool: pathologically significant but may not produce signs of bleeding early detection of colorectal cancer principle: PSEUDOPEROXIDASE ACTIVITY OF HEMOGLOBIN chromogens in order of decreasing sensitivity:

o benzidineo ortho-tolidineo gum guaiac: routine

commercial testing kitso Guaiac-impregnated filter paper: feces + H2O2

Contraindications: 3 days:

o red meato horseradisho melono raw broccolio cauliflowero radisho turnipo Vitamin Co Iron supplements

7 dayso Aspirino NSAIDs other than Acetaminophen

Hemoquanto fluorometric test for hemoglobin and porphyrin

Immunochemical Fecal Occult Blood Test (iFOBT)o specific for the globin portion of human hemoglobin and uses anti-human hemoglobin Abs

QUANTITATIVE FECAL FAT TESTING

confirmatory test for steatorrhea Van de Kamer titration (gold standard) 3-day specimen with a regulated intake of fat (100 g/d) fecal lipids are converted to fatty acids and titrated to a neutral endpoint with NaOH

Coefficient of fat retention = (dietary fatfecal fat)

dietary fat

ACID STEATOCRITo rapid test to estimate amount of fat excretiono monitor therapy and screen for steatorrhea in pediatric populations

NEAR-INFRARED REFLECTANCE SPECTROSCOPY (NIRA)o 48-72hr stool that does not require reagents after homogenizationo reflectance of fecal surface + IR light between 1400 nM and 2600 nMo quantitates water, fat and nitrogen in g/24h

X 100


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APT TEST (FETAL HEMOGLOBIN)

grossly bloody stools and vomitus: SWALLOWING MATERNAL BLOOD DURING DELIVERY material is emulsified in water to release Hb, centrifuged, + 1% NaOH to pink Hb-containing supernatant in the presence of alkali-resistant fetal Hb, the solution remains pink (Hb F), whereas denaturation of the maternal Hb

(Hb A) produces a yellow-brown supernatant after standing for 2 minutes

the test can also distinguish fetal Hb from Hb A, Hb AS, CS and SS stool specimens should be tested when fresh

FECAL ENZYMES

supplied by the pancreas for digestion of dietary proteins, carbohydrates and fats decrease (pancreatic insufficiency) is associated with chronic pancreatitis and cystic fibrosis steatorrhea occurs, presence of undigested food in feces analysis focuses on TRYPSIN, CHYMOTRYPSIN and ELASTASE I Trypsin: (historically) absence has been screened for by exposing x -ray paper to stool emulsified in water

o If present: it digests gelatin on the papero Detects only severe cases of pancreatic insufficiencyo False-negative results: intestinal degradation of trypsin and possibly trypsin inhibitors in feces, bacterial enzymes

Chymotrypsin: more resistant to intestinal degradation, more sensitive indicator of less severe cases of pancreaticinsufficiency

o remains stable in feces for 10 days at RTo also capable of gelatin hydrolysis but most frequently measured spectrophotometrically

Elastase I: isoenzyme of elastase; enzyme form produced by pancreaso strongly resistant to degradationo 6% of secreted pancreated enzymeso pancreas-specific with concentrations 5X higher than in pancreatic juiceo not affected by motility disorders and mucosal defectso measured using ELISA that provides a very sensitive indicator of exocrine pancreatic insufficiency

CARBOHYDRATES

an increase indicates OSMOTIC DIARRHEA by the osmotic pressure of unabsorbed sugar in intestine drawing in fluid andelectrolytes

may be present due to:o intestinal inability to absorb carbohydrates: CELIAC DISEASEo lack of digestive enzymes such as lactase: LACTOSE INTOLERANCE

Carbohydrate malabsorption or intolerance (maldigestion): primarily analyzed by serum and urine testso COPPER REDUCTION TEST (Clinitest tablet) in fecal specimen

Detects congenital disaccharidase deficiencies as well as enzyme deficiencies due to nonspecificmucosal injury

Infant diarrhea: fecal carbohydrate testing + pH determinationo normal pH of feces: 7.08.0o carbohydrate disorders: pH 5.5

fecal analysis

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