Which collection tube is used for biochemistry tests and endocrinology testing and does not contain anticoagulant?

• A. Lavender-top tube
• B. Red-top tube
• C. Serum gel tube
• D. Green-top tube

Answer: (C)

For biochemistry and endocrinology tests you want a serum sample, not plasma, because many chemical and hormone measurements are made on serum. To get serum, the collection tube must allow blood to clot and not contain anticoagulants.

A serum gel tube contains a clot activator to speed clotting and a gel that, after centrifugation, forms a barrier between the serum and the clot. Since there’s no anticoagulant, the liquid you obtain is serum rather than plasma, and the gel helps keep the serum clean and stable for accurate analysis. This combination—no anticoagulant plus the gel separator—is why it’s the preferred tube for many biochemistry and endocrinology assays.

Lavender-top tubes contain EDTA, which prevents clotting and is used for hematology. Green-top tubes contain heparin, another anticoagulant, useful for plasma tests. Red-top tubes have no additive, but they don’t include the gel separator, so they don’t offer the same serum-separation advantages.