In most hospitals, blood samples are collected and analyzed in standardized blood tubes, also called vacutainers. These are sterile plastic or glass tubes that can be distinguished by color-coded plastic caps (Figure 1).
Most blood collection tubes contain additives, such as anticoagulants, that mix with the collected blood. The addition of additives further determines the type of hematology analysis performed with the respective blood sample The additives are indicated by the color of the plastic cap (Figure 2).

Figure 1: Different blood collection tubes.

Figure 2: Color tube guide showing the different types of tubes and their use in the lab.