A sediment with two crystal populations

A clean-catch urine specimen reaches the bench 25 minutes after collection. Fresh sediment microscopy shows a few colorless bipyramidal forms and a few fine yellow-brown granules against a background of 0 to 2 red cells and 0 to 2 white cells per high-power field. The urine is pH 5.5 and specific gravity 1.028, both inside this laboratory's reference intervals. Nothing on the dipstick is positive, and the specimen looks unremarkable except for those two crystal populations.

A second aliquot from the same specimen sits in the refrigerator for 4 hours while other work is processed, then returns to room temperature for 20 minutes before repeat microscopy. The bipyramidal forms look the same. The fine yellow-brown granules do not; there are now many of them, enough that an automated flag reads possible storage-related crystallization. Nothing about the patient changed between those two examinations. Something about the specimen did.

pH, solubility, polarization, and specimen history let a technologist narrow a crystal identification without memorizing every published shape. Crystal identification by morphology is probabilistic, not a name-by-picture exercise, and a single photograph is never enough evidence on its own. The reasoning separates a defensible morphology-based call from a storage artifact and from a pattern that needs a second look.

When a crystal population changes between a fresh and a held aliquot, that change is data about the specimen's handling, not automatically a new patient finding.