OSMT (Ontario Society of Medical Technologists) Practice Exam

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What is drawn when a CBC is ordered?

Several citrate tubes
Several SST tubes
One heparin tube
One EDTA tube

The correct answer is: One EDTA tube

When a Complete Blood Count (CBC) is ordered, the correct specimen that is drawn is an EDTA tube. EDTA, or ethylenediaminetetraacetic acid, is an anticoagulant that is commonly used in laboratory settings to prevent blood from clotting. This is essential for a CBC because the test analyzes the components of the blood, including red blood cells, white blood cells, and platelets. Using EDTA ensures that the blood cells remain in their natural state for accurate counting and analysis. The other options involve different blood collection methods or additives that are not suitable for CBC tests. Citrate tubes are typically used for coagulation studies, SST tubes (serum separator tubes) are used for serum tests and may not preserve cellular components adequately, and a heparin tube is not ideal for a CBC as it may interfere with the cellular morphology observed during analysis. Therefore, drawing blood into an EDTA tube is the best practice for obtaining a sample for a CBC.