NEPHROLITHIASIS

Question 1

Which of the following is the most common type of kidney stone?
A. Calcium phosphate
B. Uric acid
C. Struvite
D. Calcium oxalate

Answer 1

D. Calcium oxalate

Rationale: Calcium oxalate stones account for approximately 75% of all kidney stones, making them the most common type.

Question 2

Which type of kidney stone is most commonly associated with infection by urease-producing bacteria?
A. Uric acid
B. Struvite
C. Calcium phosphate
D. Cystine

Answer 2

B. Struvite

Rationale: Struvite stones are often associated with infections caused by urease-producing bacteria, such as Proteus species. These bacteria create an alkaline environment that facilitates struvite stone formation.

Question 3

Which kidney stone type is least common?
A. Uric acid
B. Struvite
C. Cystine
D. Calcium phosphate

Answer 3

C. Cystine

Rationale: Cystine stones are rare, accounting for less than 1% of all kidney stones. They are associated with a genetic disorder called cystinuria.

Question 4

Which of the following is the most clinically significant urinary inhibitor of calcium-containing kidney stone formation?
A. Uric acid
B. Citrate
C. Magnesium
D. Oxalate

Answer 4

B. Citrate

Rationale: Citrate is the most clinically important inhibitor of calcium-containing stones. It binds calcium in the urine, reducing the availability of free calcium for crystal formation.

Question 5

What is the primary determinant of crystal formation in urine?
A. Urinary volume
B. Urinary pH
C. Supersaturation
D. Presence of bacteria

Answer 5

C. Supersaturation

Rationale: Supersaturation occurs when the concentration product of a solute exceeds its solubility product, promoting crystal formation. However, inhibitors like citrate often prevent stones from forming despite supersaturation.

Question 6

Which of the following dietary factors is associated with an increased risk of kidney stone formation?
A. Potassium
B. Animal protein
C. Calcium
D. Phytate

Answer 6

B. Animal protein

Rationale: Animal protein increases the risk of kidney stone formation by contributing to increased urinary excretion of calcium, uric acid, and oxalate while reducing urinary citrate.

Question 7

Higher dietary calcium intake is associated with a lower risk of stone formation primarily due to which mechanism?
A. Increased urinary citrate levels
B. Reduced absorption of dietary oxalate in the intestine
C. Direct inhibition of urinary calcium excretion
D. Increased urinary magnesium levels

Answer 7

B. Reduced absorption of dietary oxalate in the intestine

Rationale: Dietary calcium binds oxalate in the intestine, reducing its absorption and subsequent urinary excretion, thereby lowering the risk of calcium oxalate stone formation.

Question 8

What is the likely reason calcium supplements may increase the risk of kidney stone formation compared to dietary calcium?
A. Supplemental calcium has a higher bioavailability than dietary calcium.
B. Calcium supplements lead to higher urinary citrate levels.
C. The timing of calcium supplementation may lead to increased urinary calcium excretion.
D. Calcium supplements reduce intestinal absorption of magnesium.

Answer 8

C. The timing of calcium supplementation may lead to increased urinary calcium excretion.

Rationale: Calcium supplements may not coincide with oxalate-containing meals, leading to increased calcium absorption and excretion in the urine, which raises the risk of stone formation.

Question 9

Which statement about dietary oxalate and kidney stone formation is true?
A. Most dietary oxalate is highly bioavailable.
B. Urinary oxalate is a weak risk factor for calcium oxalate stone formation.
C. Stone formers may absorb more dietary oxalate than non-stone formers.
D. Avoiding dietary oxalate does not affect stone formation risk.

Answer 9

C. Stone formers may absorb more dietary oxalate than non-stone formers.

Rationale: Increased oxalate absorption in stone formers leads to higher urinary oxalate, which is a strong risk factor for calcium oxalate stone formation.

Question 10

Why are vitamin C supplements associated with an increased risk of calcium oxalate stone formation in men?
A. They reduce urinary citrate levels.
B. They lead to hypercalciuria.
C. They increase oxalate levels in the urine.
D. They reduce intestinal calcium absorption.

Answer 10

C. They increase oxalate levels in the urine.

Rationale: Vitamin C is metabolized to oxalate, leading to increased urinary oxalate levels and raising the risk of calcium oxalate stone formation in male stone formers.

Question 11

What is the role of vitamin B6 in patients with type 1 primary hyperoxaluria?
A. It reduces urinary oxalate levels.
B. It decreases urinary citrate levels.
C. It increases calcium absorption in the gut.
D. It lowers urinary pH.

Answer 11

A. It reduces urinary oxalate levels.

Rationale: High doses of vitamin B6 may reduce oxalate production in patients with type 1 primary hyperoxaluria, thereby lowering urinary oxalate levels.

Question 12

Which of the following is the most readily modifiable risk factor for kidney stone formation?
A. Higher urine oxalate excretion
B. Higher urine uric acid levels
C. Lower urine citrate excretion
D. Lower urine volume

Answer 12

D. Lower urine volume

Rationale: Lower urine volume concentrates lithogenic factors and increases the risk of stone formation. Higher fluid intake to increase urine volume has been proven effective in reducing stone recurrence.

Question 13

How does higher dietary calcium intake reduce the risk of calcium oxalate stone formation?
A. By increasing urine calcium excretion
B. By reducing gastrointestinal oxalate absorption
C. By promoting urinary citrate excretion
D. By decreasing serum parathyroid hormone (PTH) levels

Answer 13

B. By reducing gastrointestinal oxalate absorption

Rationale: Dietary calcium binds to oxalate in the gut, reducing oxalate absorption and subsequent urine oxalate excretion, which decreases the risk of calcium oxalate stone formation.

Question 14

Which factor reduces urinary citrate excretion, thereby increasing the risk of calcium-containing stone formation?
A. Low dietary oxalate intake
B. High dietary potassium intake
C. Metabolic acidosis
D. Increased fluid intake

Answer 14

C. Metabolic acidosis

Rationale: Metabolic acidosis, often due to high animal protein intake, increases citrate reabsorption in the proximal tubules, leading to lower urinary citrate levels and higher stone risk.

Question 15

Which type of kidney stone formation is influenced by urine pH levels consistently ≤5.5?
A. Calcium oxalate stones
B. Calcium phosphate stones
C. Uric acid stones
D. Cystine stones

Answer 15

C. Uric acid stones

Rationale: Uric acid stones form in acidic urine with a pH ≤5.5, as uric acid becomes less soluble in acidic environments.

Question 16

Which stone type is more likely to form in urine with a pH ≥6.5?
A. Uric acid stones
B. Calcium oxalate stones
C. Calcium phosphate stones
D. Struvite stones

Answer 16

C. Calcium phosphate stones

Rationale: Calcium phosphate stones form in alkaline urine (pH ≥6.5) because phosphate is less soluble at higher pH levels.

Question 17

Which statement about urine pH and kidney stone formation is correct?
A. Calcium oxalate stones form only in acidic urine.
B. Cystine is more soluble in acidic urine.
C. Uric acid stones require consistently low urine pH for formation.
D. Calcium phosphate stones are pH-independent.

Answer 17

C. Uric acid stones require consistently low urine pH for formation.

Rationale: Uric acid stones depend on a consistently acidic environment (pH ≤5.5) for crystallization, while other stones, like calcium oxalate, are not directly influenced by urine pH.

Question 18

Which type of kidney stone is not directly influenced by urine pH?
A. Uric acid stones
B. Calcium phosphate stones
C. Calcium oxalate stones
D. Cystine stones

Answer 18

C. Calcium oxalate stones

Rationale: Calcium oxalate stone formation is independent of urine pH, whereas other stone types like uric acid, calcium phosphate, and cystine are pH-sensitive.

Question 19

Which condition warrants immediate urologic intervention in a patient with kidney stones?
A. A stone measuring <6 mm with no signs of infection
B. Presence of intractable pain despite medical management
C. A stone with a high likelihood of spontaneous passage
D. An asymptomatic stone without urinary tract infection (UTI)

Correct Answer:

Answer 19

B. Presence of intractable pain despite medical management

Rationale: Intractable pain is a key indication for urologic intervention to provide relief and prevent further complications.

Urologic intervention should be postponed unless there is evidence of UTI, a low probability of spontaneous stone passage (e.g., a stone measuring ≥6 mm or an anatomic abnormality), or intractable pain.

Question 20

What is the threshold stone size above which spontaneous passage is considered unlikely, often necessitating urologic intervention?
A. ≥4 mm
B. ≥5 mm
C. ≥6 mm
D. ≥8 mm

Answer 20

C. ≥6 mm

Rationale: Stones measuring ≥6 mm are less likely to pass spontaneously, and intervention may be necessary depending on clinical circumstances.

Question 21

Which type of bacteria is most commonly associated with the formation of struvite stones?
A. Escherichia coli
B. Proteus mirabilis
C. Staphylococcus aureus
D. Pseudomonas aeruginosa

Correct Answer:

Answer 21

B. Proteus mirabilis

Rationale: Struvite stones form only in the presence of urease-producing bacteria like Proteus mirabilis, which hydrolyzes urea and raises urine pH.

Struvite stones, also known as infection stones or triplephosphate stones, form only when the upper urinary tract is infected with urease-producing bacteria such as Proteus mirabilis, Klebsiella pneumoniae, or Providencia species

Question 22

What is the characteristic pH level of urine in patients with struvite stones?
A. <5.5
B. 5.5–6.5
C. 6.5–7.5
D. >8.0

Answer 22

D. >8.0

Rationale: Urease activity elevates the urine pH to a supraphysiologic level (>8.0), facilitating struvite stone formation.

Question 23

What is the most effective management strategy for struvite stones?
A. Long-term antibiotic therapy
B. Acidification of urine with dietary modifications
C. Complete surgical removal of the stones
D. Increased fluid intake and conservative management

Answer 23

C. Complete surgical removal of the stones

Rationale: Struvite stones require complete removal by a urologist, as they can grow quickly and form staghorn calculi.