Final answer:
Red topped tubes do not contain anticoagulants and are used for serum collection in which collected blood is allowed to clot.
Step-by-step explanation:
No anticoagulants are found in red topped tubes. Blood collection tubes are color-coded to denote the type of additives they contain. For example, lavender topped tubes usually contain EDTA, which is an anticoagulant. Green topped tubes typically contain heparin, another type of anticoagulant. Yellow topped tubes may contain anticoagulants or other additives depending on the specific tests they are designed for. However, red topped tubes are typically used for serum collection and do not contain any anticoagulants. When blood is collected in these tubes, the blood clots, and the serum is separated by centrifugation.