Which tube is drawn first in the typical order of draw?

• A. Blood cultures
• B. Discard
• C. Light blue
• D. Red

Answer: (A)

The main idea here is that the order of draw is chosen to keep samples as pure and accurate as possible. Blood culture tubes are drawn first because they require a sterile collection to detect any microbes in the blood. If you draw other tubes first, additives or substances from those tubes (like anticoagulants or clot activators) or skin flora from the venipuncture site could contaminate the culture or alter its growth, leading to misleading results. By starting with the blood cultures, you minimize the risk of contamination and ensure the culture result reflects the patient's true condition. The other tubes come later because they contain additives needed for other tests (light blue for coagulation studies, red for serum chemistry, etc.), and drawing them afterward reduces the chance of interfering with culture results. The discard tube is used only to waste a small amount when necessary, not as the primary sample for cultures.