Question

What is NOT true with regard to 'triple' stones?

• A. Struvite stones are composed of triple phosphate
• B. They are called staghorn calculi when they are formed in the renal pelvis
• C. Form in acidic urine
• D. Associated with UTI

Hint:

Struvite (triple phosphate) stones need alkaline urine from urease producing bacteria to form.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
"Triple" stones is another name for struvite stones. We need the one statement about them that is false.

Step 2: Key Concept:
Struvite stones are made of magnesium ammonium phosphate, which is why they are called triple phosphate stones (three components: magnesium, ammonium, and phosphate). They form only in the presence of urease producing bacteria, most commonly Proteus, which split urea into ammonia and raise the urine pH. This means struvite stones need alkaline urine to form, not acidic urine.

Step 3: Detailed Explanation:
Statement (A), struvite stones are composed of triple phosphate, is a correct definition of the stone.
Statement (B), they are called staghorn calculi when formed in the renal pelvis, is also correct. Because urease splitting bacteria keep making alkaline, ammonia rich urine, the stone keeps growing to fill the renal pelvis and calyces, forming a branching staghorn shape.
Statement (C), form in acidic urine, is false. Struvite crystals are unstable in acidic urine and only precipitate when the urine pH rises above about 7, which happens because of urease producing organisms.
Statement (D), associated with UTI, is correct, since struvite stones cannot form without a urease producing urinary tract infection driving the alkaline environment.

Step 4: Final Answer:
The false statement is that triple stones form in acidic urine, they actually need alkaline urine to form.