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°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.
Keywords: amorphous urates; crystal solubility; microscopy; urinalysis; urine crystals; urine sediment.
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