NHA Phlebotomy Certification Practice Exam

Which color tube is typically used for collecting blood for a complete blood count (CBC)?

1. Green

2. Blue

3. Red

4. Purple

The correct answer is: Purple

The purple tube is used for collecting blood for a complete blood count (CBC) because it contains an anticoagulant, typically ethylenediaminetetraacetic acid (EDTA). This additive prevents the blood from clotting, allowing for accurate analysis of the cellular components of blood, such as red blood cells, white blood cells, and platelets. The preservation of blood cells in their original state is critical for determining various parameters that characterize the blood’s health and functionality. In contrast, the other colors mentioned do not contain the appropriate additive for this specific test: the green tube typically contains heparin, which is used for different types of tests; the blue tube is usually filled with citrate for coagulation studies; and the red tube, which does not contain any additives, is often used for serum tests, not for tests requiring whole blood components. Thus, for a CBC, the use of the purple tube is essential to maintain the integrity of the blood sample.