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Protocols to Dissolve Amorphous Urate Crystals in Urine
Journal article   Peer reviewed

Protocols to Dissolve Amorphous Urate Crystals in Urine

Kristina Jackson Behan and Michael A. Johnston
Laboratory medicine, Vol.53(3), pp.e63-e68
05/05/2022
DOI: https://doi.org/10.1093/labmed/lmab088
PMID: 34643240
Web of Science ID: WOS:000763963400001

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Abstract

Objective Amorphous urate crystals can obscure significant findings during a routine urinalysis. There is no standardized protocol to minimize their effect. Materials and Methods We tested 210 urine specimens. Three specimens had high red blood cell (RBC) or white blood cell (WBC) counts. Fifty-six specimens formed amorphous urates. Sediment from these specimens was treated with 50 mM sodium hydroxide (NaOH) at a 1:2 and/or 1:4 dilution. We warmed 22 specimens with crystals at various temperatures. Results Amorphous urate crystals formed in concentrated urine with an acidic pH. Adding 50 mM NaOH dissolved amorphous urates, revealing the presence of underlying bacteria and yeast, but WBC and RBC counts were grossly decreased. Prewarming unspun specimens to 60 degrees C for 90 seconds dissolved most amorphous urates. Conclusion The protocol to eliminate amorphous urate crystals is to prewarm the specimen before testing. Adding 50 mM NaOH to sediment dissolves amorphous urates to enhance the visibility of bacteria and yeast but has a deleterious effect on WBC and RBC.

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