Blood Tests

Your Care Explained > Tests and Procedures : Blood Tests

Because the by-products of bodily processes like respiration and metabolism are taken up by the blood as it circulates through the body, blood tests help doctors assess how well organ systems are functioning, identify risk factors and determine whether medical treatments are working.

What to Expect:

  • Some blood tests require overnight fasting.
  • Focus on something else if you don’t like the sight of blood.
  • If a bruise forms, ice will reduce the swelling.
Enlarge this Image image

Preparing for a Blood Test

Few blood tests require advance preparation, with the exception of glucose and cholesterol tests, which may require overnight fasting. If you are having a blood test, you may want to wear a top with short sleeves or with long sleeves that can be easily rolled or pushed above your elbow.

Having a Blood Test

If you feel faint at the thought of having blood taken, you can ask to lie down during the test. You may also want to turn your head away while blood is being withdrawn.

The phlebotomist will wrap a tourniquet on your arm a few inches above the elbow, and ask you to make a fist. He or she may tighten the tourniquet until the veins of your inner arm become raised, and swab the skin over a prominent vein with alcohol.

Using a hollow needle attached to thin tubing, the phlebotomist will pierce your skin and the vein. You will feel light pressure and perhaps a stinging sensation as the needle is inserted. Your blood will flow through the tubing into a small vial. The phlebotomist may clamp the tubing and change vials, if several different blood analyses are prescribed.

After the necessary blood is withdrawn, the phlebotomist will remove the needle and tape a gauze patch over the needle-prick. You may be asked to put gentle pressure on the gauze to aid clotting. Occasionally, blood may leak into the surrounding tissues before a clot has formed, producing a bruise. If so, you may want to hold an ice pack over the area to reduce swelling.

Learning Your Results

Each vial of blood will be analyzed separately in a pathology laboratory and the results forwarded to your doctor. Your doctor should notify you of the results and discuss what they mean for you within a week or two.

Date Last Modified: January 21, 2011

Send Feedback To: BWH Women’s Health at

75 Francis Street, Boston, MA 02115 617.732.5500
harvard medical school partners healthcare © BWH 2011