Which tubes contain no additives and do not require inversion?

• A. Red top tubes.
• B. Green top tubes.
• C. Lavender top tubes.
• D. Gray top tubes.

Answer: (A)

The concept here is which tubes are used for serum and have no additives, so there’s nothing to mix. The red top tube is the plain, additive-free option. Because there’s no additive to disperse or anticoagulant to distribute, there’s no need to invert it—allowing the blood to clot and then separating serum by centrifugation.

Green top tubes contain heparin (an anticoagulant) and require mixing to distribute it properly. Lavender top tubes contain EDTA and gray top tubes contain glycolysis inhibitors with oxalate; both categories need inversion to ensure the additives are evenly distributed and the specimen remains stable.