MEDT 208 Urinalysis: fecal analysis study objectives
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| What is the mechanism of secretory diarrhea? | Increased intestinal secretion of solute causes increased fluid volume in large intestine; exceeds absorptive threshold of large intestine.
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| What is the mechanism of osmotic diarrhea? | Ingestion of large quantity of osmotically active solutes causes additional excretion of water & electrolytes into lumen. Fluid volume exceeds threshold of large intestine. (Increased osmotic gap).
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| How are maldigestion & malabsorption related to diarrhea? | Both result in abnormally increased qty of food to large intestine. Food is osmotically active, which cause retention of large qty water and electrolytes in intestinal lumen = diarrhea.
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| What is maldigestion? | Inability to convert food into readily absorbable substances. Pancreatic digestive enzymes or bile salts for fat emulsion & lipase activation missing/deficient.
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| What is malabsorption? | Normal digestive ability w/inadequate intestinal absorption of pre-processed foods.
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| What is the osmolar gap? | The difference between measured & calculated fecal osmolality.
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| What is the osmolar gap value for osmotic diarrhea? | > 20 mOsm/kg
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| What is the osmolar gap value for secretory diarrhea? | 10-20 mOsm/kg
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| What are the macroscopic features of normal feces? | Brown, formed, unremarkable odor, cylindrical or tubular shape.
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| What causes clay, gray, pale or white stool? | Post-hepatic obstruction OR barium
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| What causes red stool? | Blood (lower GI), beets, food dye, drugs
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| What causes black stool? | Blood from upper GI, Iron, charcoal, bismuth
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| What causes green stool? | Green veggies, biliverdin (antibiotic therapy)
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| What causes hard stools? | Constipation/dehydration
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| What causes soft stools? | Increased fecal water content
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| What causes watery stools? | Diarrhea, steatorrhea
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| What causes narrow, ribbon-like stools? | Bowel obstruction
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| What causes small, round stools? | Constipation
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| What causes bulky stools? | Steatorrhea
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| What is the primary purpose of the microscopic examination for fecal leukocytes? | differential diagnosis of diarrhea; or detect invasive, inflammatory conditions.
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| What is the basic procedure for qualitative assessment of fecal fat using a microscopic examination? | Increased fat seen macroscopically, confirmed microscopically with Sudan III or IV, oil red O stains.
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| What color do neutral fecal fats stain? | red-orange
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| What is the clinical utility of quantitative fecal fat tests? | Screening for steatorrhea.
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| Which fecal fats are present in maldigestion? | Increased neutral fats
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| Which fecal fats are present in malabsorption? | Normal fats + Increased total fats
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| List at least five causes of blood in feces. | (1) Colorectal cancer; (2) Aspirin and anti-inflammatory medications; (3) Red meat; (4) Horseradish, raw broccoli, cauliflower, radishes, turnips; (5) Melons; (6) Menstrual and hemorrhoid contamination
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| Why is detection of fecal occult blood important, and what is it recommended for? | Importance of fecal occult blood detection: recommended annual screening for colorectal cancer.
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| What is the principle of the Guiac-based test for fecal occult blood? | Pseudoperoxidase activity of hemoglobin.
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| What is the principal of the Immmunochemical test for fecal blood? | Polyclonal antibodies
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| What is the principle of the Apt test (fetal hemoglobin)? | Alkaline resistance of fetal hemoglobin. In alkaline media, F-hemoglobin reacts differently than adult hemoglobin.
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| What is the key sample requirement for the Apt test? | MUST contain fresh blood.
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| A pink supernatant in the Apt test indicates? | alkali-resistant fetal Hgb b/c not degraded by NaOH.
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| A yellow-brown supernatant in the Apt test indicates? | Maternal Hgb present, degraded by NaOH
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| What effect does disaccharidase deficiency has on fecal characteristics and formation? | Results in bacterial fermentation of disaccharides, which causes production of large amounts of intestinal gas, diarrheal stools w/characteristic decreased pH (5.0/6.0).
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| State two methods for the qualitative detection of abnormal quantities of fecal carbohydrates. | (1) Clinitest (presence of carbs/reducing sugars); (2)Rapid qualitative fecal pH (carbs --> characteristically reduced pH 5.0-6.0)
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| What is the purpose of the xylose absorption test? | Differentiate carb metabolism VS. carb maldigestion.
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| What is the principle of the xylose absorption test? | D-xylose is normally easily absorbed by the intestines. When problems with absorption occur, D-xylose is not absorbed by the intestines, and its level in blood and urine is low.
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| How can the presence of steatorrhea be screened for by testing a random stool sample? | Sudan III staining
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| What confirmatory test should be performed for steatorrhea? | quantitative fecal fat
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| Describe the appearance of the stool specimens if steatorrhea is present. | Bulky, frothy
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| If a pancreatic insufficiency is suspected, what two tests that can be performed on a stool specimen to aid in the diagnosis. | Chymotrypsin and elastase 1
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| What diagnostic tests or procedures are used to diagnose cystic fibrosis? | CF mutation panel; Sweat chloride; Nasal (transepithelial) Potential Difference (NPD)
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| A 70-year-old woman suffering from arthritis takes the occult blood screening test as part of a routine physical. The results of all three specimens are positive for occult blood. What's a possible nonpatholgic cause for the unexpected results? | Patient is taking large amounts of aspirin
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| Bob is a 50-year-old man advised by the doctor to lose 30 lb. He has been doing well on a high-protein, low carbohydrate diet. Two of his three specimens are positive for occult blood. What is a possible nonpathologic cause for the unexpected results? | Bob is eating primarily red meat
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| A watery black stool from a neonate is received in the laboratory with requests for an Apt test, fecal pH, and a Clinitest. Which of these tests can not be performed on this specimen? (Apt, Clinitest, Fecal pH) | Apt (hemoglobin already denatured)
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| What is a possible cause of black stool in infants? | Infant ingested maternal blood
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| Which of the following tests is not performed to detect osmotic diarrhea? (Flintiest, fecal fats, fecal neutrophils, muscle fibers) | Muscle fibers
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| What is the fecal test that requires a 3-day specimen? (Fecal occult blood, APT test, Elastase I, Quantitative fecal fat testing) | Quantitative fecal fat testing
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| Large orange-red droplets seen on direct microscopic examination of stools mixed with Sudan Ill represent: | Neutral fats
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| The term "occult" blood describes blood that: | Is not visibly apparent in the stool specimen
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| What is the recommended number of samples that should be tested to screen for occult blood result? | Two samples taken from different parts of three stools
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| Which test is the most sensitive to upper Gl bleeding? | Hemoquant
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| Annual testing for fecal occult blood has a high predictive value for the detection of: | Colorectal cancer
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| Tests for the detection of "occult" blood rely on the: | Pseudoperoxidase activity of hemoglobin
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| What is the significance of an APT test that remains pink after addition of sodium hydroxide? | Fetal hemoglobin is present.
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