This blood test can be done at any time in a lab, hospital or doctor’s office.
A tourniquet or rubber strap is tied around the upper arm to gently keep blood in the vein. Then, a needle with an attached container is inserted into a vein. Often, a large vein in the bend of the elbow or the top of the hand is used. After the container is filled, the needle is removed and a bandage is placed to stop the bleeding.
In newborn infants and small children, veins may be hard to find. A finger prick may be all that’s needed to collect a blood sample.
The entire test takes less than five minutes and is not too uncomfortable. Some people see a slight bruise at the puncture site for a day or two after this test.