What are the needle sizes used in phlebotomy?

In phlebotomy, the most commonly used needle sizes are 21-gauge and 22-gauge needles. A 21-gauge needle is typically used for adult blood draws, as it provides a good balance between blood flow and patient comfort. The 22-gauge needle is often used for pediatric patients or those with smaller veins. Larger needles, like 18-gauge, are sometimes used for blood donation or specific medical procedures.