Microscopic: microorganisms, contaminants and artifacts

6 ASCP MLS practice questions on Microscopic: microorganisms, contaminants and artifacts, 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 · Medium

   Which contaminant shows a Maltese cross under polarized light and can be mistaken for a fat droplet?

   1. AAir bubbles
   2. BOil droplets
   3. CClothing fibers
   4. DStarch granules

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   Answer: D · Starch granules

   Starch granules, for example from body powders, are refractile and often have a central dimple. Under polarized light they show a Maltese cross, like cholesterol droplets in oval fat bodies and fatty casts. Starch lies free in the sediment rather than inside cells or casts, and the protein pad is not raised as in nephrotic syndrome. Correlating the sediment with the chemical results avoids a false report of lipiduria.

   • A: Air bubbles are refractile but do not polarize.
   • B: Oil droplets look like fat but do not show a Maltese cross.
   • C: Fibers polarize light but do not show a Maltese cross.

2. Question 2 · Hard

   A 3-hour-old urine from a 27-year-old woman with vaginal discharge contains several round, nonmotile cells about the size of white cells. Trichomoniasis is suspected. What is the best next step?

   1. AReport white cells and take no further action
   2. BRefrigerate the sample and re-examine it later
   3. CSuggest a nucleic acid amplification test
   4. DReport Trichomonas vaginalis as present

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   Answer: C · Suggest a nucleic acid amplification test

   Trichomonads lose motility as the specimen ages and cools, and nonmotile forms round up and look like white cells. Without the typical jerky movement they should not be reported. Nucleic acid amplification tests (NAAT) are far more sensitive than wet-mount microscopy and are the recommended test, on vaginal swabs or urine. A positive result means treating the patient and her sexual partners.

   • A: Ignoring the clinical suspicion misses a common, treatable infection.
   • B: Cooling stops motility further, so re-examining later makes identification harder.
   • D: Nonmotile forms cannot be reliably told apart from white cells.

3. Question 3 · Medium

   Bacteria in a urine sediment are most likely to mean a urinary tract infection when they are found:

   1. AWith many squamous cells in a midstream sample
   2. BIn a sample held 5 hours at room temperature
   3. CWith many white cells in a fresh, clean-catch sample
   4. DIn urine taken from a catheter drainage bag

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   Answer: C · With many white cells in a fresh, clean-catch sample

   Bacteria multiply quickly in urine left at room temperature and enter easily from skin and vaginal flora, so their presence alone is not diagnostic. They are significant in a fresh, properly collected sample, especially with white cells and a positive leukocyte esterase or nitrite. Culture with a colony count confirms infection. Bacteria are reported as few, moderate or many per HPF.

   • A: Many squamous cells suggest contamination, which also brings bacteria.
   • B: Bacteria multiply after collection when urine is not refrigerated.
   • D: Urine in a drainage bag has stood for hours, and bacteria grow there.

4. Question 4 · Easy

   Trichomonas vaginalis should be reported in a urine sediment only when the organism:

   1. AIs seen with clue cells
   2. BIs seen with many white cells
   3. CStains with Sternheimer-Malbin
   4. DShows its typical jerky motility

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   Answer: D · Shows its typical jerky motility

   T. vaginalis is a pear-shaped flagellate with an undulating membrane, and its rapid, jerky movement is what identifies it. When it stops moving it rounds up and looks like a white cell or a renal tubular cell. Nonmotile forms should therefore not be reported. Fresh, warm specimens show motility best.

   • A: Clue cells indicate bacterial vaginosis, not trichomoniasis.
   • B: White cells come with many infections and do not identify the parasite.
   • C: Staining does not identify trichomonads; motility does.

5. Question 5 · Easy

   Clothing or diaper fibers in a urine sediment are most often mistaken for:

   1. AMucus threads
   2. BCasts
   3. CCrystals
   4. DFungal hyphae

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   Answer: B · Casts

   Fibers from clothing, diapers or tissue are long, flat and more refractile than most casts, so they can be mistaken for casts, especially waxy ones. Unlike casts, they usually polarize light. They often lie near the edges of the coverslip. Reporting a fiber as a cast could wrongly suggest kidney disease.

   • A: Mucus threads are wavy ribbons of low refractility, unlike flat, bright fibers.
   • C: Crystals have regular geometric shapes, unlike long fibers.
   • D: Fungal hyphae are branched and segmented, unlike flat fibers.

6. Question 6 · Medium

   A woman with poorly controlled diabetes has glucose 4+ on the reagent strip. Her sediment shows small, refractile ovals with buds and some branching filaments. They are most likely:

   1. ACandida albicans
   2. BRed blood cells
   3. CTrichomonas vaginalis
   4. DCalcium oxalate monohydrate

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