Microscopic examination: crystals and other elements

15 DOH Abu Dhabi (HAAD) lab licensing practice questions on Microscopic examination: crystals and other elements, part of Urinalysis and Body Fluids. The first 15 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 49-year-old woman with type 2 diabetes started empagliflozin, a sodium-glucose cotransporter-2 (SGLT2) inhibitor, 2 months ago and now has vulval itching. Her fresh urine: SG 1.025, pH 5.5, glucose 4+, blood negative, ascorbic acid negative, nitrite and leukocyte esterase negative; strip QC is acceptable. A trainee has reported '10-20 RBC/HPF'. On review, the colorless oval bodies vary in size, some carry small buds, a few form short branching chains, they are not birefringent under polarized light, and they stay intact after 2% acetic acid is added. The sediment should be reported as:

   1. ABudding yeast, not red cells
   2. BCalcium oxalate monohydrate ovals
   3. CRed cells missed by the blood pad
   4. DOil droplets from a lubricant

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   Answer: A · Budding yeast, not red cells

   Yeast cells are oval, vary in size and show budding and sometimes pseudohyphae, which separates them from red cells. Red cells lyse in 2% acetic acid while yeast stays intact, and the negative blood pad, with a negative ascorbic acid pad and acceptable QC, agrees that no red cells are present. Calcium oxalate monohydrate ovals are birefringent, and oil droplets are highly refractile spheres that never bud. SGLT2 inhibitors cause heavy glycosuria, which favors Candida growth in the genital and urinary tract. Report the yeast and correct the red cell count.

   • B: Calcium oxalate monohydrate is birefringent and does not bud.
   • C: The blood pad is negative with acceptable QC and no ascorbic acid, and red cells would lyse in acetic acid.
   • D: Oil droplets are refractile spheres that do not bud or form chains.

2. Question 2 · Hard

   A 58-year-old woman with a long-standing staghorn stone in her right kidney has recurrent urinary infections with Proteus mirabilis. A midstream urine examined 15 minutes after collection gives: SG 1.012, pH 8.5, nitrite positive, leukocyte esterase 2+, protein trace. The sediment shows many white cells and bacteria and many colorless three- to six-sided prisms, some shaped like coffin lids, which dissolve when dilute acetic acid is added. Her serum calcium, phosphate and urate are normal, and she takes no medicines. Which crystal is present, and what is its significance?

   1. AStruvite, formed by urea-splitting bacteria
   2. BCalcium oxalate, from hypercalciuria
   3. CCystine, from a tubular transport defect
   4. DStruvite, formed in vitro after standing

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   Answer: A · Struvite, formed by urea-splitting bacteria

   Colorless coffin-lid prisms in alkaline urine that dissolve in dilute acetic acid are triple phosphate (struvite, magnesium ammonium phosphate). Proteus mirabilis makes urease, which splits urea into ammonia; this raises the urine pH and supplies the ammonium that forms struvite, the mineral of staghorn stones. Triple phosphate also forms in old alkaline specimens, but this urine was examined within 15 minutes, so the crystals reflect the infection. Calcium oxalate forms envelopes, ovals or dumbbells that do not dissolve in acetic acid, and cystine forms hexagonal plates in acidic urine. Struvite stones keep growing while the urease-producing infection persists.

   • B: Calcium oxalate forms envelopes or dumbbells and does not dissolve in acetic acid.
   • C: Cystine forms hexagonal plates in acidic urine, not prisms in alkaline urine.
   • D: The urine was examined within 15 minutes, too soon for crystals to form on standing.

3. Question 3 · Medium

   In a patient with acute liver failure, the urine contains yellow-brown spheres with concentric rings and fine radial striations. What are they most likely to be?

   1. ATyrosine crystals
   2. BCalcium carbonate crystals
   3. CLeucine crystals
   4. DAmmonium biurate crystals

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   Answer: C · Leucine crystals

   Leucine crystals are yellow-brown, oily-looking spheres marked with concentric circles and radial lines. They are abnormal and are found with tyrosine crystals in severe liver disease, or in some inherited disorders of amino acid metabolism. They are seen less often than tyrosine, which is much less soluble. They should be reported together with the liver history and the bilirubin results.

   • A: Tyrosine forms fine needles in sheaves or rosettes, not ringed spheres.
   • B: Calcium carbonate forms small colorless spheres and dumbbells in alkaline urine.
   • D: Ammonium biurate forms spiky 'thorny apple' spheres in old alkaline urine.

4. Question 4 · Hard

   A 45-year-old with Crohn disease, after removal of 1 m of ileum, has fatty stools, recurrent kidney stones and many calcium oxalate crystals in fresh urine. What is the main cause of his high urine oxalate?

   1. AEthylene glycol taken in error is metabolized to oxalate
   2. BFatty acids bind gut calcium, leaving oxalate free to be absorbed
   3. CHis liver lacks an enzyme and overproduces oxalate
   4. DExcess vitamin C from supplements is converted to oxalate

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   Answer: B · Fatty acids bind gut calcium, leaving oxalate free to be absorbed

   In fat malabsorption, unabsorbed fatty acids bind calcium in the gut lumen, so less calcium is left to bind dietary oxalate. The free oxalate is absorbed in the colon, whose permeability is also raised by unabsorbed bile salts, and is excreted in the urine, where it forms calcium oxalate. This enteric hyperoxaluria is a well-known cause of stones after ileal disease or resection. Treatment includes a low-fat, low-oxalate diet, a high fluid intake and calcium taken with meals.

   • A: Ethylene glycol poisoning causes acute acidosis, not recurrent stones.
   • C: Primary hyperoxaluria is an inherited liver enzyme defect, usually found in childhood.
   • D: Large vitamin C doses can raise oxalate, but nothing here suggests them.

5. Question 5 · Hard

   A 40-year-old receiving high-dose intravenous acyclovir for herpes encephalitis has a creatinine rise from 75 to 240 µmol/L (0.85 to 2.7 mg/dL) in 2 days. Fresh urine, pH 5.5, shows many fine, colorless, strongly birefringent needles. He takes no other medicines, and liver tests are normal. The needles are most likely:

   1. ATyrosine crystals
   2. BAmpicillin crystals
   3. CSulfonamide crystals
   4. DAcyclovir crystals

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   Answer: D · Acyclovir crystals

   Acyclovir is poorly soluble in urine, and rapid intravenous doses in a poorly hydrated patient can make it precipitate in the tubules. The crystals are fine, colorless, birefringent needles, and the tubular blockage causes acute kidney injury within a day or two of starting the drug. The medicine history identifies them, because several drug crystals look alike. Slower infusions, good hydration and dosing adjusted to renal function prevent it.

   • A: Tyrosine needles occur in severe liver disease, and his liver tests are normal.
   • B: Ampicillin can form similar needles, but he is not receiving it.
   • C: Sulfonamide crystals are yellow-brown and need a sulfonamide history.

6. Question 6 · Easy

   Which of these urine crystals is regarded as abnormal whenever it is seen?

   1. AUric acid
   2. BCalcium oxalate dihydrate
   3. CTyrosine
   4. DAmorphous urates

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7. Question 7 · Hard

   A jaundiced man with hepatitis takes no medicines. Urine: pH 6.0, bilirubin pad 3+, tablet bilirubin test positive. The sediment has small clumps of bright yellow-brown needles and granules, some lying on white cells. These are most likely:

   1. AAmmonium biurate crystals
   2. BSulfonamide crystals
   3. CLeucine crystals
   4. DBilirubin crystals

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8. Question 8 · Medium

   A patient receiving high-dose intravenous ampicillin has an acidic urine that, after refrigeration, contains long, thin, colorless needles in bundles. Liver tests are normal. The needles are most likely:

   1. AAmpicillin crystals
   2. BSulfonamide crystals
   3. CCalcium phosphate crystals
   4. DTyrosine crystals

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9. Question 9 · Hard

   A urine refrigerated overnight shows many calcium oxalate dihydrate crystals. A fresh sample from the same patient, examined within an hour at room temperature, shows none. The best interpretation is:

   1. AEthylene glycol poisoning that has since cleared
   2. BThe crystals formed in vitro on cooling and are not significant
   3. CFresh urine dissolves crystals, so future samples should be chilled
   4. DIntermittent hyperoxaluria that needs a 24-hour oxalate

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10. Question 10 · Medium

    Thin, colorless hexagonal plates are found in a urine of pH 5.5. Which finding favors a hexagonal form of uric acid over cystine?

    1. ATheir presence in an acidic urine
    2. BSolubility in dilute hydrochloric acid
    3. CA positive cyanide-nitroprusside test
    4. DStrong birefringence in many colors

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11. Question 11 · Medium

    Small, colorless dumbbells and spheres in an alkaline urine release gas bubbles when dilute acetic acid is added. What are they?

    1. ACalcium oxalate monohydrate crystals
    2. BAmmonium biurate crystals
    3. CCalcium carbonate crystals
    4. DAmorphous phosphates

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12. Question 12 · Easy

    A urine with protein 4+ contains oval fat bodies and large, flat, colorless plates with a notch cut from one corner. There has been no recent imaging. What are the plates most likely to be?

    1. AUric acid crystals
    2. BCystine crystals
    3. CCholesterol crystals
    4. DRadiographic contrast media

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13. Question 13 · Medium

    A urine sediment contains plant cells with thick walls, striated meat fibers and many mixed bacteria. The most likely explanation is:

    1. AFecal contamination of the specimen
    2. BAcute bacterial pyelonephritis
    3. CVaginal contamination of the specimen
    4. DStarch powder from examination gloves

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14. Question 14 · Hard

    During a high-dose methotrexate infusion, a child's urine pH by reagent strip falls to 6.0. The protocol requires a pH of at least 7.0. Why does this result need prompt action?

    1. AAcidic urine speeds methotrexate breakdown to toxic forms
    2. BThe drug forms calcium oxalate crystals in acidic urine
    3. CMethotrexate can precipitate in the tubules in acidic urine
    4. DAcidic urine blocks the effect of leucovorin rescue

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15. Question 15 · Hard

    A trainee reports 'many uric acid crystals' in a fresh urine that has a reagent strip pH of 8.0. The crystals are yellow-brown. What should the supervisor do?

    1. AChange the pH to acidic, since the crystals prove it
    2. BReport them, as uric acid crystals can form at any pH
    3. CReport them as amorphous urates, which favor alkaline urine
    4. DRe-examine the crystals, as uric acid should not form at pH 8.0

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