Which test requires a whole blood specimen?

The correct answer is the complete blood count (CBC), which requires a whole blood specimen because this test analyzes several components of the blood, including red blood cells, white blood cells, hemoglobin, hematocrit, and platelets. For accurate results, the CBC is performed using the entirety of the blood sample, as it needs to assess both the cellular components and the overall status of the blood.

Whole blood contains all the cellular elements and plasma in their natural proportions, which is essential for the reliable evaluation of these blood components. In contrast, tests like a comprehensive metabolic panel or lipid profile typically require serum or plasma, which is obtained by allowing the blood to clot and then separating the liquid portion. While bacterial cultures can be conducted on whole blood, they can also be performed using other types of specimens, making CBC the most distinct in its requirement for whole blood.