Which color-top tube is typically used for plasma chemistry tests requiring rapid plasma separation, and what additive does it contain?

• A. Lavender-top tubes contain EDTA and are used for CBC.
• B. Gray-top tubes contain fluoride/potassium oxalate.
• C. Red-top tubes contain no additive.
• D. Green-top (heparin) or PST; contains heparin (and gel in PST)

Answer: (D)

When a test needs plasma rather than serum and you want it ready quickly, you use a green-top tube or a plasma separator tube. The essential feature is the anticoagulant: heparin, typically sodium or lithium heparin, which prevents blood from clotting so you obtain plasma. If you’re using a plasma separator tube (PST), it also contains a gel that creates a barrier between plasma and cells after centrifugation, speeding the separation process. This combination—heparin as the anticoagulant, and gel in the PST—is ideal for rapid plasma chemistry testing.

Lavender-top tubes with EDTA are for complete blood counts; gray-top tubes with fluoride/oxalate are used for glucose testing (to inhibit glycolysis); red-top tubes have no additive and yield serum after clotting, not plasma.