Which of the following sites is the first choice for drawing blood?

The median cubital vein is the first choice for drawing blood because it is typically the largest and most centrally located vein in the antecubital fossa (the area of the arm before the elbow). This vein is relatively superficial, making it easily accessible for venipuncture. It generally has fewer surrounding nerves and arterial structures, which decreases the risk of complications during the procedure. Additionally, the median cubital vein tends to be more stable and less likely to move during the blood draw, which helps to ensure a successful collection.

In comparison, while the radial artery and femoral vein can also be used for certain procedures, they are not standard sites for blood draws. The radial artery is primarily accessed for arterial blood gases or blood pressure readings, while the femoral vein poses a greater risk for complications due to its deeper location and the proximity of major blood vessels and nerves. The cephalic vein, although also used for venipuncture, is generally smaller than the median cubital vein and can be less reliable due to its more variable location and potential for rolling during the puncture. Therefore, the median cubital vein remains the preferred choice in most clinical scenarios for drawing blood samples.