What type of sample is typically used for a complete blood count?

A complete blood count (CBC) is a diagnostic test that evaluates various components of the blood, including red blood cells, white blood cells, hemoglobin levels, and platelets. The sample used for a CBC is whole blood because it contains both the cellular components and the plasma, allowing for an accurate assessment of all blood parameters. This comprehensive view of blood components is essential for diagnosing a range of conditions, including anemia, infections, and other hematological disorders.

While serum and plasma are components derived from whole blood, they lack the cellular elements needed for a complete blood count. Serum is obtained after coagulation and does not contain clotting factors or cells, making it unsuitable for this particular test. Plasma, on the other hand, is the liquid portion of blood that includes clotting factors and is often used for other types of testing, but for a CBC, whole blood is preferred because it maintains the integrity of all blood components in their natural state. Urine is entirely unrelated to a CBC, as it is a waste product of the kidney and does not provide information about blood cells. Therefore, whole blood is the correct choice for performing a complete blood count.