Which blood tube can be used for urea?

• A. Fluoride oxalate (yellow)
• B. EDTA (purple)
• C. Sodium citrate (blue)
• D. Heparin (green)

Answer: (A)

Choosing the right blood collection tube hinges on the additive inside and how it affects the assay. For measuring urea, you want a tube that prevents clotting and doesn’t interfere with the enzymatic methods used to quantify urea. The fluoride-oxalate tube provides anticoagulation (oxalate) and includes fluoride, which inhibits glycolysis. While glycolysis mainly impacts glucose testing, this combination helps preserve the sample’s integrity and compatibility with many chemistry assays, including urea, especially if there’s any delay before analysis.

In contrast, EDTA can bind metal ions and alter enzyme activity, citrate can change pH and interfere with calcium-dependent steps, and heparin can cause matrix effects in some assays. These factors can skew the measurement of urea in routine testing, making fluoride-oxalate the most suitable option among the ones listed.