Which tube must be used when drawing a CBC?

The correct choice for drawing a Complete Blood Count (CBC) test is the lavender tube. This tube contains EDTA, an anticoagulant that prevents the blood from clotting. This is crucial for a CBC as the test requires the analysis of whole blood components, including white blood cells, red blood cells, and platelets. If the blood were to clot, it would compromise the accuracy of the test results by affecting the counts and proportions of these cells.

In contrast, other tube types do not contain the appropriate anticoagulant for this specific test. The red tube, for example, is typically used for serum tests and does not contain any additives, thus allowing blood to clot. The green tube contains heparin, which is suitable for certain tests but not for a CBC, as it may interfere with cell morphology and counts. The blue tube contains sodium citrate, primarily used for coagulation studies, rather than for a CBC. Therefore, using the lavender tube is essential for obtaining reliable and precise results for a Complete Blood Count.