How It Is Done continued...
A sample of blood from an artery is usually taken from the inside of the wrist (radial artery), but it can also be taken from an artery in the groin (femoral artery) or on the inside of the arm above the elbow crease (brachial artery). You will be seated with your arm extended and your wrist resting on a small pillow. The health professional drawing the blood may rotate your hand back and forth and feel for a pulse in your wrist.
To prevent the chance of damaging the artery of the wrist when the blood sample is taken, a procedure called the Allen test may be done to make sure that blood flow to your hand is normal. An ammonia test will not be done on an arm used for dialysis or if there is an infection or inflammation in the area of the puncture site.
The health professional taking a sample of your blood will:
- Clean the needle site with alcohol. You may be given an injection of local anesthetic to numb that area.
- Put the needle into the artery. More than one needle stick may be needed.
- Allow the blood to fill the syringe. Be sure to breathe normally while your blood is being collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put a bandage over the puncture site and apply firm pressure for 5 to 10 minutes (possibly longer if you take blood-thinning medicine or have bleeding problems).
How It Feels
If the sample is taken from a vein
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
If the sample is taken from an artery
Collecting blood from an artery is more painful than collecting it from a vein because the arteries are deeper and are protected by nerves.
- Most people feel a brief, sharp pain as the needle to collect the blood sample enters the artery. If you are given a local anesthetic, you may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin.
- You may feel more pain if the person drawing your blood has a hard time finding your artery, your artery is narrowed, or if you are very sensitive to pain.