A fluoride-preserved sample used for glucose testing is requested to be used for BUN testing on an automated analyzer using the urease method. How should you respond?

A fluoride-preserved sample used for glucose testing is requested to be used for BUN testing on an automated analyzer using the urease method. How should you respond?

• A. Will gladly do the test if sufficient specimen remains
• B. Could do the test using a micromethod
• C. Can do the BUN determination on the automated analyzer
• D. Cannot perform the procedure

Answer: (D)

Fluoride-preserved specimens are used to inhibit glycolysis for glucose testing, but that same preservative can interfere with urease-based BUN assays. The urease method relies on the enzyme’s activity to break down urea and produce a measurable signal, and the fluoride in the tube can inhibit or alter that reaction, making results unreliable. Because this sample is preserved with fluoride, it cannot be used for BUN testing on the automated analyzer. A new specimen collected in a fluoride-free tube (or as your lab protocol specifies) is required for an accurate BUN result.

Fluoride-preserved specimens are used to inhibit glycolysis for glucose testing, but that same preservative can interfere with urease-based BUN assays. The urease method relies on the enzyme’s activity to break down urea and produce a measurable signal, and the fluoride in the tube can inhibit or alter that reaction, making results unreliable. Because this sample is preserved with fluoride, it cannot be used for BUN testing on the automated analyzer. A new specimen collected in a fluoride-free tube (or as your lab protocol specifies) is required for an accurate BUN result.