A fluoride tube sample collected for glucose is also requested to be used for BUN determination via the urease method on an automated analyzer. What should you tell the physician?

A fluoride tube sample collected for glucose is also requested to be used for BUN determination via the urease method on an automated analyzer. What should you tell the physician?

• 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)

When a specimen’s collection tube additives can interfere with an assay, you must consider compatibility before running the test. Sodium fluoride in a fluoride-oxalate tube is great for inhibiting glycolysis to preserve glucose, but it also can inhibit enzymatic reactions used in other tests. The urease-based BUN method on an automated analyzer relies on enzymatic activity to convert urea to ammonia and drive a color change; fluoride ions can inhibit urease or the subsequent reactions, making the result unreliable. Because of this interference, you cannot perform the BUN test on this specimen from the fluoride tube, even if some sample remains. Request a new specimen collected in a tube appropriate for the BUN assay (not containing fluoride/oxalate) so the analyzer can give accurate results.

When a specimen’s collection tube additives can interfere with an assay, you must consider compatibility before running the test. Sodium fluoride in a fluoride-oxalate tube is great for inhibiting glycolysis to preserve glucose, but it also can inhibit enzymatic reactions used in other tests. The urease-based BUN method on an automated analyzer relies on enzymatic activity to convert urea to ammonia and drive a color change; fluoride ions can inhibit urease or the subsequent reactions, making the result unreliable. Because of this interference, you cannot perform the BUN test on this specimen from the fluoride tube, even if some sample remains. Request a new specimen collected in a tube appropriate for the BUN assay (not containing fluoride/oxalate) so the analyzer can give accurate results.