Phlebotomy is the process in which a needle is temporarily inserted into a vein through a cut (incision) or puncture so as to obtain a sample of blood. This is done for analysis of the blood sample to diagnose various disorders. It can also be done as part of the patient’s treatment in case of certain diseases.
The most common procedure is by performing a venipuncture (collecting blood from veins).
In certain cases, blood may be collected by finger stick sampling (when a minute quantity of blood is required) or by heel stick sampling (in case of newborn baby or infant).
A person who performs phlebotomy is called a phlebotomist. These are people who are specially trained to draw blood from a patient.
Phlebotomy can be performed by phlebotomists, doctors, nurses, or lab technicians.
Indications of Phlebotomy
- Diagnostic purpose: to obtain blood for analysis and diagnosis of various disorders:
- analyzing and quantifying various biochemical parameters in the body like blood sugar, cholesterol, uric acid, blood gases, etc.
- measurement and morphological assessment of blood components (complete blood counts including red blood cells, white blood cells, and platelets).
- culture and antibiotic sensitivity of blood in case of septicemia.
- Therapeutic purpose: removal of blood for treatment of high levels of iron (as in hemochromatosis, thalassemia, etc) or red blood cells (as in polycythemia)
- To collect blood for later uses, like blood donation.
Contraindications for Phlebotomy
- Skin conditions like cellulitis or abscess that can cause direct seeding of infectious agents (e.g. bacteria) into the blood.
- Venous fibrosis on palpation
- Presence of a hematoma (bleeding under the skin)
- Presence of a vascular shunt or graft
- Presence of a vascular access device
Sites of Phlebotomy
Venous blood is most commonly obtained from the superficial veins of the upper limb. In case the veins of the upper limb are not available [trauma to both upper limbs or if the previous sampling has rendered the veins fibrotic], blood may be obtained from other sites.
The most commonly used veins are
There include three prominent veins in the antecubital area (front of the elbow). The most prominent and easily accessible vein should be used.
Median cubital vein: It is the first choice for blood collection as it is a large, superficial vein and does not bruise easily. A deep puncture should not be done otherwise there is a risk of penetration of biceps tendon and brachial artery.
Cephalic vein: It is the second choice for blood collection. It runs superficially under the skin along the outer side of the arm and forearm.
Basilic vein: It is the third choice for blood collection. It is a superficial vein running along the inner side of the arm and forearm. Due to the proximity of nerves, it is a high-risk area. Also, this vein tends to roll away and bruise more easily.
Dorsal metacarpal veins
These veins are present on the backside (posterior surface) of the hand and thumb side (lateral aspect) of the wrist. They are however not as large as the antecubital veins. Drawing blood from these veins is more painful because the hand is a sensitive area.
Veins of the ankle and foot
The top of the foot and side of the ankle can also be used for venipuncture. Phlebotomy at these sites carries an increased risk of clot formation. Also, there is an increased risk of infection, especially in diabetics.
Phlebotomy should not be performed at the following sites:
- Vein having IV infusion line: The blood sample withdrawn may get diluted with IV solution and produce erroneous results.
- The arm on side of the mastectomy: There is a high risk of infection and lymphedema.
- Fistula or shunt: Surgically prepared access point for dialysis should be avoided as there is a risk of damage and infection.
- Hematomas or sites of tattoo: The blood sample withdrawn may get contaminated with tissue fluid or with lead from tattoo ink.
- Scarred areas from burns and surgery: Such a site is difficult to puncture and should be avoided.
Arterial Blood Sample
The artery is a less common site for blood collection. The most common reason for taking blood from the artery is arterial blood gas (ABG) analysis.
The most common sites are the radial artery at the wrist and the femoral artery in the groin. An arterial catheter can also be used to draw blood.
In contrast to venous sampling, withdrawal of an arterial blood sample requires more extensive training.
It is taken when only minute quantities of the blood are required as in blood glucose analysis by glucometer method.
The most common site is the finger. It can also be done from the heel in neonates.
The best locations for fingersticks are the center of the finger pads of the 3rd (middle) and 4th (ring) fingers of the non-dominant hand. The tip of the finger or the center of the finger should not be used. The sides of the finger where there is less soft tissue should also be avoided. The 2nd (index) finger tends to have thicker, callused skin. The fifth finger tends to have less soft tissue overlying the bone. Fingers that are cold or cyanotic, swollen, scarred, or covered with a rash should also be avoided.
It is the recommended location for blood collection in a newborn baby or infant.
Procedure of Venipuncture
- The patient can be made to sit in a chair, or sitting or lying on a bed.
- An elastic band/ tourniquet is tied around the arm/ site. The band/tourniquet retains blood within the arm and makes the veins more visible.
- The patient is asked to make a fist.
- The vein is felt by palpation and an appropriate site for puncture is selected.
- The skin over the area is cleaned with an antiseptic.
- Use the thumb to draw the patient’s skin taut and anchor the vein.
- The needle is inserted into the vein keeping the beveled side of the needle up.
- As soon as blood enters the hub of the needle, the blood is sucked into vacutainer. In the case of a syringe, the plunger is pulled back to allow the filling of the blood.
- The appropriate amount of blood is drawn and when it is about to complete, remove the tourniquet.
- The needle is withdrawn from the vein.
- Pressure is applied to the puncture site with a cotton swab to stop bleeding. A bandage may be applied.
Patients who experience swelling of the puncture site or continued bleeding after phlebotomy should seek immediate medical treatment.
In cases when a large amount of blood is withdrawn (as in blood donation), patients should be asked to drink plenty of fluids and eat regularly over the next 24 hours to replace lost blood volume.
Vein visualization device is available these days which displays veins beneath the skin surface. This greatly helps healthcare professionals in finding a good vein for venipuncture and eliminates the need for multiple pricks. It is especially useful in obese persons, dark-skinned individuals, small children, burn victims or drug abusers where vein visualization remains a challenge.
Amount of Blood Withdrawn During Phlebotomy
The amount of blood drawn depends on the purpose of the procedure.
- The volume of blood needed for the diagnostic purposes may vary from 2-10 cm or more depending upon the test being performed and the number of tests.
- In therapeutic phlebotomy, around 450-500 ml of blood is removed during each session. Repeated phlebotomies may need to be performed at regular intervals depending upon the patient’s condition. For example, in the case of hemochromatosis, initially, the phlebotomies may be performed every week or fortnight (for up to a year) until iron levels are brought to normal range. After this, blood may be removed every two to three months for the rest of the patient’s life.
- Blood donors usually contribute a unit of blood (500 ml) in a session.
Risks or Complications of Phlebotomy
Bruising and soreness
Mostly patients have a small bruise or mild pain at the venipuncture site for a few days.
Similar to any invasive procedure, there is a small risk of infection of the vein (phlebitis) or overlying skin (cellulitis) which can be reduced by using prepackaged sterilized equipment and following proper aseptic technique. There is no risk of transmitting HIV or hepatitis infection through this procedure since all needles are disposed of after a single-use.
To prevent it, the patient is asked to apply direct pressure on the site with a cotton gauze for at least 5 minutes. Patients on anticoagulant therapy might need to apply pressure for a longer time.
In rare cases, during the procedure, a nearby nerve may get touched by the needle resulting in sharp pain. In such a case, the needle should be removed immediately and phlebotomy should be performed at some other site.
If this occurs, remove the needle and apply direct pressure for at least 10 minutes. If a pulsatile mass persists, arterial duplex ultrasonography may be considered.
Some patients manifest a vasovagal response during or just after the procedure. To prevent this, the blood should be withdrawn with the patient in the lying down position. Also, the patient should be encouraged to look away from the phlebotomy site, equipment, and blood-filled tubes.
Order of Draw
The term order of draw is the sequence in which tubes should be filled. The order of draw is important in vacutainer as the needle which pierces the tubes can carry additives from one tube into the next, and cause cross-contamination.
The order of draw is as follows:
- First – blood culture bottle or tube (yellow or yellow-black top)
- Second – coagulation tube (light blue top).
- Third – non-additive tube (red top)
- Last draw – additive tubes in this order:
- SST (red-gray or gold top). Contains a gel separator and clot activator.
- Sodium heparin (dark green top)
- PST (light green top). Contains lithium heparin anticoagulant and a gel separator.
- EDTA (lavender top)
- Oxalate/fluoride (light gray top) or other additives
How to Prevent Hemolysis While Taking a Blood Sample
- Avoid excessive fist clenching.
- Avoid massaging, squeezing, or probing the venipuncture site.
- Avoid prolonged tourniquet application.
- Avoid traumatic venipuncture.
- If using a needle and syringe, avoid drawing the plunger back too forcefully.
- If blood flow into the tube slows, adjust the needle position to remain in the center of the lumen.
- Mix the blood gently. Do not shake vigorously
- Giavarina D, Lippi G. Blood venous sample collection: Recommendations overview and a checklist to improve quality. Clin Biochem. 2017;50(10-11):568-573.
- Lippi G, Blanckaert N, Bonini P, Green S, Kitchen S, Palicka V, Vassault AJ, Mattiuzzi C, Plebani M. Causes, consequences, detection, and prevention of identification errors in laboratory diagnostics. Clin Chem Lab Med. 2009;47(2):143-53.
- Lippi G, Salvagno GL, Montagnana M, Franchini M, Guidi GC. Phlebotomy issues and quality improvement in results of laboratory testing. Clin Lab. 2006;52(5-6):217-30.
- World Health Organization. WHO guidelines on drawing blood: best practices in phlebotomy. https://www.ncbi.nlm.nih.gov/books/NBK138650/pdf/Bookshelf_NBK138650.pdf