Feces examination

6 DOH Abu Dhabi (HAAD) lab licensing practice questions on Feces examination, part of Urinalysis and Body Fluids. The first 6 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 55-year-old man has weight loss and pale, bulky, foul-smelling stools. Sudan III without acid shows over 60 large orange droplets per high-power field. Fecal elastase-1 is 45 µg/g (reference above 200 µg/g). The most likely cause is:

   1. APancreatic insufficiency
   2. BLactase deficiency
   3. CCeliac disease
   4. DCrohn's disease of the ileum

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   Answer: A · Pancreatic insufficiency

   Many neutral fat droplets on the slide without acid mean that fat is reaching the stool undigested, because pancreatic lipase is lacking. A fecal elastase-1 below 200 µg/g, and especially below 100 µg/g, confirms exocrine pancreatic insufficiency, often from chronic pancreatitis. In celiac or ileal disease, fat is digested but not absorbed, so the extra fat is mainly fatty acids and fecal elastase is usually normal. A watery stool can give a falsely low elastase through dilution, so a formed sample is preferred.

   • B: Lactase deficiency causes watery, acidic stools, not steatorrhea.
   • C: Celiac disease gives mainly split fat, with a normal elastase.
   • D: Ileal Crohn's disease impairs absorption, not pancreatic digestion, so elastase stays normal.

2. Question 2 · Medium

   A 6-year-old has fever, cramps and frequent small stools with mucus. A methylene blue stool preparation shows many neutrophils. The most likely cause is:

   1. ANorovirus
   2. BShigella species
   3. CVibrio cholerae
   4. DGiardia duodenalis

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   Answer: B · Shigella species

   Neutrophils enter the stool when bacteria invade and inflame the colonic mucosa, as with Shigella, Campylobacter and nontyphoidal Salmonella. In cholera, viral gastroenteritis and giardiasis the organisms do not invade the mucosa, so leukocytes are few or absent. Amoebic dysentery also shows few neutrophils, because Entamoeba histolytica destroys them. The finding guides culture but has modest sensitivity, and lactoferrin or calprotectin tests are often used instead.

   • A: Norovirus infects the small bowel without bringing neutrophils into the stool.
   • C: Cholera toxin causes watery diarrhea without mucosal invasion or neutrophils.
   • D: Giardia attaches to the small bowel lining without causing a neutrophil influx.

3. Question 3 · Easy

   Fecal leukocytes are looked for in a wet preparation of stool stained with:

   1. AMethylene blue
   2. BLugol's iodine
   3. CKinyoun carbol fuchsin
   4. DSudan III

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   Answer: A · Methylene blue

   A drop of fresh stool or mucus is mixed with Loeffler methylene blue, which stains white cell nuclei so that neutrophils are easy to see and count. Gram and Wright stains on a dried smear are alternatives. Many neutrophils suggest invasive bacterial infection or inflammatory bowel disease. Because the cells break down quickly, the stool must be fresh; fecal lactoferrin or calprotectin tests are more stable alternatives.

   • B: Iodine shows protozoan cysts and undigested starch.
   • C: Kinyoun stain shows acid-fast parasites such as Cryptosporidium.
   • D: Sudan III stains neutral fat for the fecal fat screen.

4. Question 4 · Medium

   A stool is screened for fat with Sudan III. Slide 1 (no acid) shows a few small orange droplets, within normal limits. Slide 2 (acetic acid and heat) shows over 100 large orange droplets per high-power field. The pattern suggests:

   1. AMaldigestion, as in pancreatic insufficiency
   2. BNormal fat digestion and absorption
   3. CMineral oil laxative contamination
   4. DMalabsorption, as in celiac disease

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   Answer: D · Malabsorption, as in celiac disease

   Slide 1 stains neutral fat (triglyceride). Slide 2 is acidified and heated, which turns soaps into fatty acids so that the total fat, including the fatty acids, is stained. Normal neutral fat with a raised total fat means fat was digested to fatty acids but not absorbed, the pattern of intestinal malabsorption such as celiac disease. Pancreatic insufficiency leaves fat undigested, so neutral fat is raised on slide 1; a 72-hour quantitative fecal fat confirms steatorrhea.

   • A: Maldigestion raises neutral fat on slide 1, which is normal here.
   • B: Over 100 droplets per field on slide 2 is increased fat.
   • C: Mineral oil appears as neutral fat droplets on slide 1.

5. Question 5 · Easy

   Fecal immunochemical tests (FIT) for occult blood detect the:

   1. APeroxidase activity of heme
   2. BIron released from hemoglobin
   3. CPorphyrins derived from heme
   4. DGlobin of human hemoglobin

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   Answer: D · Globin of human hemoglobin

   FIT uses antibodies against the globin of human hemoglobin. Globin from bleeding high in the gut is digested on the way down, so FIT mainly detects lower-gut (colorectal) bleeding. Animal hemoglobin in meat and plant peroxidases are not detected, so no diet restriction is needed. FIT has replaced guaiac tests in many colorectal cancer screening programs.

   • A: Guaiac tests detect the peroxidase-like activity of heme.
   • B: Neither type of occult blood test measures iron.
   • C: Porphyrin-based methods measure heme-derived porphyrins, not globin.

6. Question 6 · Medium

   Which of these can make a guaiac fecal occult blood test falsely negative?

   1. ARaw horseradish
   2. BDaily aspirin
   3. CRare red meat
   4. DHigh-dose vitamin C

   Answer and explanation in LearnFree account