Venipuncture is the method by which blood is drawn in most cases, and it may also be called phlebotomy or a blood draw. It refers to using a needle to pierce the skin and to access a vein so that a small amount of blood can be removed for various studies. Most people will experience venipuncture at some time in their lives, to either test for disease or to evaluate the various elements in blood that might indicate poor health.
The majority of adults will have blood drawn from the inside of the elbow, where the phlebotomist or other medical technician or specialist can access the median cubital vein. The standard method is to insert a needle through the skin and into this vein, which may first be slightly enlarged by using a tourniquet for a minute. Blood is then usually extracted by using a special vacuum tube that will hold the blood until it has various tests performed on it. Since people may require several tests from a single venipuncture, more than one vacuum tube may be used to collect the blood, but this doesn’t tend to require more than one puncture. In rare instances, a syringe method is used to collect blood instead, but the vast majority of venipuncture types use the vacuum tube.
Young children may have blood drawn done in different areas, including the hand or foot. Although this is more painful, it is usually easier to access the surface veins on infants and children from these areas. Patients or their parents can sometimes have a preference here, and moms or dads could advocate for a venipuncture performed on the median cubital vein instead, especially if a child is over a couple of months old.
For the person experiencing a blood draw, especially one fearful of needles or alarmed at the sight of blood, it can seem like the multiple tubes used to collect blood collect a lot of blood. Actually samples taken tend to be very small, though they may not look it. A single vial might contain 5 milliliters, which is equivalent to a teaspoon. This should be compared to the amount of blood a person could voluntarily donate. It takes roughly 29 milliliters to make up an ounce, and the standard blood donation is approximately 16 ounces or 473.2 ml. Though it can seem like a lot, even if several vials are used, usually no more than an ounce of blood is lost, one-sixteenth of a voluntary blood donation.
Venipuncture also occurs when people have IV (intravenous) lines started. In most cases, the skin must be pierced and a vein accessed so that fluid or medicines can be administered intravenously. The procedure for this is slightly different, and can be more involved. However, when an IV line is present, blood draws may occur through this open access, instead of having to perform additional procedures, which can be useful in hospital settings where blood tests might be required frequently.