The most painful vein to draw blood from is often the arterial vein as the arteries are deeper and have thicker and more muscular walls, and they are also surrounded by more nerves.
The sensation of an arterial blood draw or even an accidental arterial puncture is often described as intense, throbbing or shooting pain, which is a result of the high pressure the arterial artery.
Arteries are also associated closely with nerves, which means that a needle can easily irritate or strike a nerve and cause intense pain.
And unlike veins, arterial walls are also thick and muscular, which requires more pressure to puncture.
The high pressure, pulsing blood flow can also cause pain as well as swelling, or a pulsating mass also known as pseudoaneurysm if blood leaks into the surrounding tissue.
If an artery is hit, you should apply firm, direct pressure to the site for 5 to 10 minutes to prevent a hematoma.
And if the pain is severe, your arm becomes cold/pale or you experience numbness/tingling (paresthesia), seek immediate medical attention.
During blood draws, the level of pain and discomfort can vary depending on the location and your anatomy.
Some areas where blood are drawn are naturally more sensitive than others as a result of the density of nerves or the stability of the veins.
Areas such as the back of the hand or the wrist have a high concentration of nerve endings, which can also make a needle stick for a blood draw feel more pin prickly or intense, when compared to the fleshy part of your arm.
And certain nerves, like your basilic vein that is located on the inner side of your arm also run closer to major nerves and if a needle is positioned near these structures, it might cause a sharper sensation.
The median cubital vein, which is found in the center of your inner elbow, is also often preferred for blood draw, because it's often large, stable and has fewer nearby nerves that often results in less discomfort.
And even factors like skin thickness, the depth of the vein and whether the vein tends to roll or move during the blood draw can also affect your experience.
If a sharp, radiating or electric sensation is felt during a blood draw, you should notify the doctor immediately as it indicates that the needle may be near a nerve.