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Fecal Analysis
MEDT 208 Urinalysis: fecal analysis study objectives
| Question | Answer |
|---|---|
| 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. |
| 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). |
| 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. |
| What is maldigestion? | Inability to convert food into readily absorbable substances. Pancreatic digestive enzymes or bile salts for fat emulsion & lipase activation missing/deficient. |
| What is malabsorption? | Normal digestive ability w/inadequate intestinal absorption of pre-processed foods. |
| What is the osmolar gap? | The difference between measured & calculated fecal osmolality. |
| What is the osmolar gap value for osmotic diarrhea? | > 20 mOsm/kg |
| What is the osmolar gap value for secretory diarrhea? | 10-20 mOsm/kg |
| What are the macroscopic features of normal feces? | Brown, formed, unremarkable odor, cylindrical or tubular shape. |
| What causes clay, gray, pale or white stool? | Post-hepatic obstruction OR barium |
| What causes red stool? | Blood (lower GI), beets, food dye, drugs |
| What causes black stool? | Blood from upper GI, Iron, charcoal, bismuth |
| What causes green stool? | Green veggies, biliverdin (antibiotic therapy) |
| What causes hard stools? | Constipation/dehydration |
| What causes soft stools? | Increased fecal water content |
| What causes watery stools? | Diarrhea, steatorrhea |
| What causes narrow, ribbon-like stools? | Bowel obstruction |
| What causes small, round stools? | Constipation |
| What causes bulky stools? | Steatorrhea |
| What is the primary purpose of the microscopic examination for fecal leukocytes? | differential diagnosis of diarrhea; or detect invasive, inflammatory conditions. |
| 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. |
| What color do neutral fecal fats stain? | red-orange |
| What is the clinical utility of quantitative fecal fat tests? | Screening for steatorrhea. |
| Which fecal fats are present in maldigestion? | Increased neutral fats |
| Which fecal fats are present in malabsorption? | Normal fats + Increased total fats |
| 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 |
| 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. |
| What is the principle of the Guiac-based test for fecal occult blood? | Pseudoperoxidase activity of hemoglobin. |
| What is the principal of the Immmunochemical test for fecal blood? | Polyclonal antibodies |
| 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. |
| What is the key sample requirement for the Apt test? | MUST contain fresh blood. |
| A pink supernatant in the Apt test indicates? | alkali-resistant fetal Hgb b/c not degraded by NaOH. |
| A yellow-brown supernatant in the Apt test indicates? | Maternal Hgb present, degraded by NaOH |
| 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). |
| 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) |
| What is the purpose of the xylose absorption test? | Differentiate carb metabolism VS. carb maldigestion. |
| 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. |
| How can the presence of steatorrhea be screened for by testing a random stool sample? | Sudan III staining |
| What confirmatory test should be performed for steatorrhea? | quantitative fecal fat |
| Describe the appearance of the stool specimens if steatorrhea is present. | Bulky, frothy |
| 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 |
| What diagnostic tests or procedures are used to diagnose cystic fibrosis? | CF mutation panel; Sweat chloride; Nasal (transepithelial) Potential Difference (NPD) |
| 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 |
| 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 |
| 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) |
| What is a possible cause of black stool in infants? | Infant ingested maternal blood |
| Which of the following tests is not performed to detect osmotic diarrhea? (Flintiest, fecal fats, fecal neutrophils, muscle fibers) | Muscle fibers |
| 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 |
| Large orange-red droplets seen on direct microscopic examination of stools mixed with Sudan Ill represent: | Neutral fats |
| The term "occult" blood describes blood that: | Is not visibly apparent in the stool specimen |
| 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 |
| Which test is the most sensitive to upper Gl bleeding? | Hemoquant |
| Annual testing for fecal occult blood has a high predictive value for the detection of: | Colorectal cancer |
| Tests for the detection of "occult" blood rely on the: | Pseudoperoxidase activity of hemoglobin |
| What is the significance of an APT test that remains pink after addition of sodium hydroxide? | Fetal hemoglobin is present. |
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