Blood work is ordered by your physician for purposes of detecting illnesses and to gauge the amount of cholesterol, sugar and other substances in your body. Some blood tests may require fasting – your doctor will talk to you about any preparations you need to be aware of before your blood tests are conducted. Blood is usually taken from a vein in your arm or by using a finger prick. The professional taking your blood may tie a band (also known as a tourniquet) on the upper part of your arm and ask you to make a fist. This makes it easier to find your vein and insert the needle. This needle is attached to a tube that collects your blood – the amount of blood needed will depend upon the tests your doctor has issued. Once the allotted amount of blood is taken, the needle is removed and a cotton ball and band aid are usually placed to help stop additional bleeding. You may feel a slight prick when the needle is inserted and removed.