Which crystal is commonly described as having a coffin-lid appearance?

Which crystal is commonly described as having a coffin-lid appearance?

• A. Bilirubin crystal
• B. Calcium oxalate crystal
• C. Cystine crystal
• D. Triple phosphate crystal (struvite)

Answer: (D)

The shape described as coffin-lid is a hallmark of ammonium magnesium phosphate crystals, known as triple phosphate or struvite crystals. In urine sediment, these crystals are typically colorless and form in alkaline urine, often associated with infections by urease-producing bacteria. Their distinctive flat, prism-like form resembles a small coffin lid, which makes this morphologic description a reliable clue. The other crystals have different shapes: bilirubin crystals are slender yellow-green needles or plates, calcium oxalate crystals frequently look like envelopes or dumbbells, and cystine crystals are colorless hexagonal crystals. Because the coffin-lid appearance aligns specifically with struvite crystals, it’s the best description for this question.

The shape described as coffin-lid is a hallmark of ammonium magnesium phosphate crystals, known as triple phosphate or struvite crystals. In urine sediment, these crystals are typically colorless and form in alkaline urine, often associated with infections by urease-producing bacteria. Their distinctive flat, prism-like form resembles a small coffin lid, which makes this morphologic description a reliable clue. The other crystals have different shapes: bilirubin crystals are slender yellow-green needles or plates, calcium oxalate crystals frequently look like envelopes or dumbbells, and cystine crystals are colorless hexagonal crystals. Because the coffin-lid appearance aligns specifically with struvite crystals, it’s the best description for this question.