A 57-year-old man has received intravenous gentamicin for 9 days for endocarditis. His creatinine has risen from 0.9 to 2.6 mg/dL [80 to 230 µmol/L]. He has no rash, his fever has settled, and blood eosinophils are normal. Urine: SG 1.010, pH 6.0, protein 1+, glucose 1+ with a plasma glucose of 92 mg/dL [5.1 mmol/L], leukocyte esterase and nitrite negative. Sediment: many casts packed with round cells larger than neutrophils, each with one central round nucleus and no lobes; many free cells of the same type; no red cell casts. Which cast type and cause fit best?

Renal tubular cell casts; drug-induced tubular injury

White cell casts; acute pyelonephritis

Granular casts; prerenal azotemia

White cell casts; allergic interstitial nephritis

Where in the kidney are urinary casts formed?

In the distal tubules and collecting ducts

In the glomerulus and Bowman space

Which feature best separates a hyaline cast from a mucus thread?

Parallel sides with a rounded end

A location near the coverslip edge

A trainee reports no casts in a urine with protein 2+. Reviewing the same slide, the supervisor finds 6-8 hyaline casts/LPF. What most likely caused the trainee to miss them?

Scanning with the light too bright

Using phase-contrast microscopy

Scanning under the low-power objective

Looking mainly along the coverslip edges

Microscopic: casts

11 ASCP MLS practice questions on Microscopic: casts, part of Urinalysis and Body Fluids. The first 11 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 57-year-old man has received intravenous gentamicin for 9 days for endocarditis. His creatinine has risen from 0.9 to 2.6 mg/dL [80 to 230 µmol/L]. He has no rash, his fever has settled, and blood eosinophils are normal. Urine: SG 1.010, pH 6.0, protein 1+, glucose 1+ with a plasma glucose of 92 mg/dL [5.1 mmol/L], leukocyte esterase and nitrite negative. Sediment: many casts packed with round cells larger than neutrophils, each with one central round nucleus and no lobes; many free cells of the same type; no red cell casts. Which cast type and cause fit best?
1. AWhite cell casts; acute pyelonephritis
2. BGranular casts; prerenal azotemia
3. CRenal tubular cell casts; drug-induced tubular injury
4. DWhite cell casts; allergic interstitial nephritis
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Answer: C · Renal tubular cell casts; drug-induced tubular injury
Cells larger than neutrophils, with a single central round nucleus, are renal tubular epithelial cells, and casts packed with them form when injured tubular cells slough into the lumen. Gentamicin accumulates in proximal tubular cells and causes direct toxic tubular injury (acute tubular necrosis), typically after about a week of therapy. Glycosuria with a normal plasma glucose, an isosthenuric specific gravity of 1.010 and a negative esterase all fit tubular damage rather than infection. White cell casts would contain lobed, granular neutrophils and give a positive esterase. Recognizing tubular cell casts early allows the drug to be stopped or its dose adjusted.
- A: Pyelonephritis gives white cell casts with a positive esterase and bacteria; here the esterase and nitrite are negative and the cells are not lobed.
- B: Prerenal azotemia gives a concentrated urine with few hyaline or granular casts and no cellular casts.
- D: Interstitial nephritis gives white cell casts with a positive esterase, often with rash or eosinophils; these cells are tubular cells, not white cells.
Question 2 · Easy
Where in the kidney are urinary casts formed?
1. AIn the urethra during voiding
2. BIn the bladder during storage
3. CIn the glomerulus and Bowman space
4. DIn the distal tubules and collecting ducts
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Answer: D · In the distal tubules and collecting ducts
Casts form when uromodulin (Tamm-Horsfall protein) gels in the lumen of the distal tubules and collecting ducts, taking their shape. Anything in the tubule at the time, such as cells, is trapped in the cast. Casts therefore show what is happening inside the kidney. Slow urine flow and acidic, concentrated urine favour their formation.
- A: The urethra is outside the kidney.
- B: Casts cannot form in the bladder, which is outside the nephron.
- C: The glomerulus filters blood; casts form further along the nephron.
Question 3 · Medium
Which feature best separates a hyaline cast from a mucus thread?
1. AA low refractive index
2. BLong, wavy, tapering edges
3. CParallel sides with a rounded end
4. DA location near the coverslip edge
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Answer: C · Parallel sides with a rounded end
Hyaline casts take the shape of the tubule, so they have parallel sides and at least one rounded end. Mucus threads are long, irregular ribbons with no defined ends, and they are more common in urine from women. Both have a low refractive index and are best seen with reduced light. Mucus has no clinical significance, while increased casts may.
- A: Both hyaline casts and mucus have a low refractive index.
- B: Long, wavy, tapering edges describe mucus threads.
- D: Both can lie near the coverslip edge, so location does not separate them.
Question 4 · Easy
Which cast type can be seen in small numbers in healthy people, for example after strenuous exercise?
1. AFatty casts
2. BWaxy casts
3. CHyaline casts
4. DRed cell casts
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Answer: C · Hyaline casts
Hyaline casts are made almost entirely of uromodulin (Tamm-Horsfall protein) and are the most common cast. The ASCP reference range is 0-2 hyaline casts/LPF. Numbers rise for a short time after strenuous exercise, dehydration, heat exposure or emotional stress. Persistently raised numbers are seen in disease such as glomerulonephritis and congestive heart failure.
- A: Fatty casts indicate lipiduria, as in nephrotic syndrome.
- B: Waxy casts indicate prolonged stasis in chronic kidney disease.
- D: Red cell casts indicate glomerular bleeding.
Question 5 · Hard
A trainee reports no casts in a urine with protein 2+. Reviewing the same slide, the supervisor finds 6-8 hyaline casts/LPF. What most likely caused the trainee to miss them?
1. AUsing phase-contrast microscopy
2. BScanning with the light too bright
3. CScanning under the low-power objective
4. DLooking mainly along the coverslip edges
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Answer: B · Scanning with the light too bright
Hyaline casts have a refractive index close to that of urine, so they disappear when bright-field light is too strong. Casts should be scanned under low power with reduced light (condenser lowered or iris closed), or with phase contrast. Casts tend to collect near the coverslip edges, so the edges should be checked. They are then reported as the average number per LPF over at least 10 fields.
- A: Phase contrast makes low-refractility casts easier to see.
- C: Low power is the correct objective for scanning and counting casts.
- D: Casts tend to collect at the coverslip edges, so scanning there is correct.
Question 6 · Medium
Casts with a high refractive index, cracked edges and blunt ends are most associated with:
1. ARecent strenuous exercise
2. BAcute glomerulonephritis
3. CAcute pyelonephritis
4. DChronic kidney failure
Answer and explanation in LearnFree account
Question 7 · Medium
A patient has fever, flank pain, and bacteria and white cells in the urine. Which sediment finding best shows that the infection involves the kidney and not just the bladder?
1. AUrothelial (transitional) cells
2. BWhite cell casts
3. CClumps of white cells
4. DMany bacteria
Answer and explanation in LearnFree account
Question 8 · Hard
A woman with fever, flank pain and a positive nitrite has casts that appear finely granular. Which step would best show whether the granules are bacteria?
1. AExamination under polarized light
2. BStaining with Prussian blue
3. CAddition of 2% acetic acid
4. DGram stain of the sediment
Answer and explanation in LearnFree account
Question 9 · Hard
A patient with nephrotic syndrome has casts containing refractile droplets. Under polarized light some droplets show Maltese crosses and others do not. Which procedure would confirm that the non-polarizing droplets are fat?
1. AStaining with Prussian blue
2. BStaining with Sternheimer-Malbin
3. CAdding 2% acetic acid
4. DStaining with Sudan III or Oil Red O
Answer and explanation in LearnFree account
Question 10 · Medium
While urine is static in the tubule, the usual order of cast degeneration is:
1. AWaxy, fine granular, coarse granular, cellular
2. BCellular, coarse granular, fine granular, waxy
3. CFine granular, cellular, waxy, coarse granular
4. DHyaline, waxy, coarse granular, cellular
Answer and explanation in LearnFree account
Question 11 · Hard
After a hypotensive episode during cardiac surgery, a 70-year-old man's creatinine rises from 1.0 to 3.1 mg/dL (88 to 274 µmol/L) over 2 days. Urine: specific gravity 1.010, protein 1+, blood negative; many renal tubular cells, tubular cell casts and coarse muddy brown granular casts. These findings most indicate:
1. AAcute tubular necrosis
2. BAcute pyelonephritis
3. CAcute glomerulonephritis
4. DPrerenal azotemia
Answer and explanation in LearnFree account

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Microscopic: casts

Where in the kidney are urinary casts formed?

Which feature best separates a hyaline cast from a mucus thread?

Which cast type can be seen in small numbers in healthy people, for example after strenuous exercise?

A trainee reports no casts in a urine with protein 2+. Reviewing the same slide, the supervisor finds 6-8 hyaline casts/LPF. What most likely caused the trainee to miss them?

Casts with a high refractive index, cracked edges and blunt ends are most associated with:

A patient has fever, flank pain, and bacteria and white cells in the urine. Which sediment finding best shows that the infection involves the kidney and not just the bladder?

A woman with fever, flank pain and a positive nitrite has casts that appear finely granular. Which step would best show whether the granules are bacteria?

A patient with nephrotic syndrome has casts containing refractile droplets. Under polarized light some droplets show Maltese crosses and others do not. Which procedure would confirm that the non-polarizing droplets are fat?

While urine is static in the tubule, the usual order of cast degeneration is: