Extremely rare "daisy-like" crystals in urinary sediment can be due to a sampling artifact.

Manual urine sediment analysis of a sample obtained from a 5 year old child by our clinical diagnostics laboratory revealed abundant "daisy-like" crystals, which have been first described in 2004 and found to be extremely rare in a follow-up publication by the same research group. To date only 12 samples have been described in the literature containing such crystals. Upon further investigation on how the sample was obtained, we were able to reproduce the process without any biological specimen involved. We show that these crystals are in fact contaminants from the sample collection recipient itself, which was a glass recipient sterilized by the patient's family the night before sample collection, by boiling water with high calcium and magnesium content (hard water), and letting the recipient cool overnight with the water in it. The obtained abundant "daisy-like" crystals readily dissolve in acidic environment, and are composed most likely of mostly calcium carbonate. Sampling artifacts are therefore a possible explanation for at least some of the previously described "daisy-like" urinary crystals, as the formation of such crystals does not need to involve any biomolecules, only hard water and appropriate crystallization conditions for the limescale in it.

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