Final answer:
The color stopper tube used to collect a blood specimen for a complete blood count (CBC) is usually purple. EDTA is commonly used as an anticoagulant in this type of blood collection.
Step-by-step explanation:
The color stopper tube used to collect a blood specimen for a complete blood count (CBC) is usually purple. The purple stopper tube contains the anticoagulant ethylenediaminetetraacetic acid (EDTA), which prevents the blood from clotting and keeps it in a liquid state, making it suitable for analysis.
EDTA is commonly used to collect blood for CBC tests because it is an effective anticoagulant that doesn't interfere with the measurement of various blood components. It helps preserve the integrity of the blood sample by preventing clotting and maintaining the cellular elements in suspension.
Other color stopper tubes, such as red or gray tubes, may be used for different blood tests that require different additives or processing methods.