Why phlebotomy matters

Most diagnostic decisions in modern medicine including a hemoglobin level, a coagulation screen, a tumor marker, a crossmatch before transfusion start with a blood sample. If the sample is wrong, the decision built on it is wrong too. Each step in phlebotomy affects the quality of the specimen and is important for preventing laboratory error, patient injury and even death [1]. That is why a procedure that looks simple from the outside is one of the most consequential routine tasks in healthcare.

This article walks through the full phlebotomy procedure, from preparation to post-procedure care, with current best practices from WHO 2010 and CLSI PRE02 (2025) [2]. We focus on venipuncture, but the principles apply to capillary puncture and arterial sampling too.

What blood tests phlebotomy supports

Common samples drawn during routine phlebotomy include:

• Complete blood count (CBC): Checks red cells, white cells, hemoglobin, and platelets.
• Chemistry panels: Electrolytes, glucose, liver and kidney function.
• Coagulation studies: PT, APTT, fibrinogen, D-dimer.
• Hormone testing: Thyroid, reproductive hormones, cortisol.
• Blood typing and crossmatching: Pre-transfusion compatibility.
• Blood cultures: Detection of bacteremia.

A single venipuncture can fill several tubes if they are filled in the correct order. We will come back to that order.

Stage 1: Before the draw

Equipment

Set up a clean tray containing:

• Sterile needles (gauges 21–23 are standard for adults; 23–25 for smaller veins or pediatric patients)
• Evacuated blood tubes appropriate to the tests ordered
• A safety-engineered butterfly set if the patient has small or fragile veins
• 70% alcohol or chlorhexidine wipes
• Sterile gauze pads and adhesive dressings
• A tourniquet (single-patient or disinfectable)
• A sharps container within arm's reach
• Specimen labels and the test request form
• A self-sealing biohazard transport bag with a separate compartment for the form

Modern practice favors engineered safety devices for example retractable needles and shielded butterfly sets that dramatically reduce needlestick injuries.

Patient identification

This is the step most likely to cause a serious error, and the easiest to do correctly. Use two patient identifiers, ideally collected by active identification: ask the patient to state (not confirm) their full name and date of birth, then match what they say against the request form and wristband. Where available, scan the wristband barcode. Never identify a patient by room or bed number.

Reviewing the lab order

Check:

• Which tests are requested and which tubes you need
• Any special handling (e.g., samples on ice, fasting required, timed draws)
• Whether the patient has restrictions (e.g., a mastectomy on one side, an existing IV line)

Talking to the patient

A brief, clear explanation lowers anxiety more than any other intervention. Tell the patient what you are about to do, how long it will take, and what they will feel. Address concerns honestly, especially fear of needles. Obtain informed consent. If the patient is a child or carer-dependent adult, involve the parent or guardian.

Stage 2: The phlebotomy procedure

Hand hygiene and gloves

This is the foundation of infection control. Follow WHO best practice guidelines [1]: wash hands with soap and water or use an alcohol-based hand rub, then put on well-fitting non-sterile gloves. Change gloves between patients.

Patient positioning

Seat the patient in a chair with arm support, or have them lie down if there is any history of fainting. Position the arm extended, palm up, with the elbow straight. Asking the patient to make a fist gently (not pump) helps fill the veins.

Site selection: why the median cubital vein wins

The antecubital fossa — the front of the elbow — is the first-choice region for venipuncture, and within it the median cubital vein is the preferred vessel. Anatomically, it sits above the bicipital aponeurosis, a sheet of connective tissue that separates it from the median nerve and brachial artery below. That layer of protection is what makes this vein the safest choice.

The cephalic vein (on the thumb side of the forearm) is a reasonable second choice. The basilic vein is a last resort: it runs close to the median nerve and brachial artery, and accidental puncture of either can cause lasting injury.

To find the vein:

• Inspect first, then palpate gently with your index finger. Arteries pulse; thrombosed veins feel firm and cord-like and roll under the finger.
• If veins are not prominent, try lowering the arm, applying a warm compress for a few minutes, or tapping the area lightly.

Avoid drawing from:

• An artery, ever, during routine phlebotomy
• The feet, unless authorized by a clinician
• Areas with significant scarring, burns, or active inflammation
• The arm on the same side as a mastectomy (lymphedema risk)
• A site with a visible hematoma — draw distal to it if there is no alternative
• The arm above an IV line — draw from the opposite arm or below the IV
• Limbs with a fistula, vascular graft, or cannula in use
• The same arm within 10–15 minutes of a blood transfusion

Applying the tourniquet

Place the tourniquet about 7–10 cm (4–5 finger widths) above the chosen vein. Snug, not tight. Release within one minute and never beyond two minutes to avoid hemoconcentration, which falsely raises cell counts, protein, and analytes bound to protein [3]. If you need another attempt, wait at least two minutes before reapplying.

Disinfecting the site

For routine draws, wipe the site with a 70% alcohol swab in a single outward circular motion for 30 seconds. Let it air dry for another 30 seconds. Wet alcohol stings and can hemolyze the first drops of sample. Do not re-palpate the site after cleaning. For blood cultures, follow your facility's chlorhexidine or iodine protocol as different, longer contact times apply.

Performing the venipuncture

• Anchor the vein. With your non-dominant thumb, pull the skin taut 2–3 cm below the puncture site to stabilize the vein.
• Insert the needle. Hold the needle bevel-up at a 15–30 degree angle to the skin. Enter in one smooth motion. According to CLSI PRE02, you may only attempt a cautious, calculated lateral relocation if you have determined the vein's precise location; otherwise, you must immediately remove the needle, activate the safety device, and apply pressure. Blind probing is strictly prohibited [2].
• Confirm placement. A small flashback of blood into the hub or first tube confirms you are in the vein.
• Engage the tube. Push the first evacuated tube onto the needle holder. Blood should flow steadily without you pulling on it.

Order of draw (CLSI PRE02, 2025)

According to the CLSI PRE02 (8th edition, 2025) guideline, blood should be collected in the following sequence: first blood culture bottles to keep them sterile, then light blue citrate tubes for coagulation studies, followed by red, gold, or tiger-top serum tubes for chemistry and serology [2]. The full sequence:

Each tube must be gently inverted the correct number of times to mix the additive: 8–10 inversions for blood culture, green (heparin), lavender (EDTA), and gray (fluoride) tubes; 5 inversions for red speckled or gold serum separator tubes (SST); and 3-4 inversions for light blue citrate tubes. Shake vigorously and you will hemolyze the sample [2].

Preventing hemolysis

Hemolysis is the single most common cause of rejected hematology and chemistry samples [4]. Most of it is preventable:

• Use an appropriately sized needle (21–23 gauge for adults; 25 gauge or larger if using a syringe).
• Let alcohol dry completely before puncture.
• Do not pull syringe plungers forcefully.
• Release the tourniquet within one minute.
• Fill tubes to the indicated line; underfilled citrate tubes are a major source of false-prolonged PT/APTT.
• Mix by gentle inversion, never by shaking.
• Avoid drawing through a small-bore IV line where possible.

Completing the procedure

• Release the tourniquet before withdrawing the needle.
• Withdraw the needle in a smooth motion and immediately activate the safety shield.
• Apply pressure to the site with a gauze pad for at least 30 seconds, longer for patients on anticoagulants.
• Dispose of sharps directly into the sharps container. No recapping.
• Label tubes at the bedside, in front of the patient, never before the draw and never after leaving the room. Include patient name, date of birth, ID number, date, and time of collection.

Stage 3: After the draw

Patient care

Watch the site for at least a minute to confirm bleeding has stopped. Ask the patient how they feel before they stand up; vasovagal reactions are most likely in the first few minutes. Apply a fresh dressing and give post-procedure instructions: keep the dressing on for about 15 minutes, avoid heavy lifting on that arm for an hour, and report any persistent bleeding, swelling, or tingling.

Documentation

Record in the patient's chart:

• Date, time, and site of venipuncture
• Needle gauge and number of attempts
• Tubes collected
• Any complications or patient reactions
• The phlebotomist's name and signature

Special situations

Pediatric patients

Use age-appropriate language. Allow a parent to stay. Consider a topical anesthetic (with physician approval) for older children. Distraction such as toys, screens or bubbles works as well as any pharmacological measure for many kids. Choose a smaller-gauge butterfly set, and remember that heel sticks in infants must be on the medial or lateral plantar surface, never the posterior curvature, to avoid hitting the calcaneus.

Elderly patients

Veins are often more fragile and roll easily. Anchor firmly, use a smaller-gauge butterfly, and avoid prolonged tourniquet time. Review medications: warfarin, DOACs, and antiplatelets prolong post-procedure bleeding.

Patients with bleeding disorders

For patients with hemophilia, von Willebrand disease, or on therapeutic anticoagulation, apply firm pressure for several minutes or longer if directed and document carefully. Coordinate with the treating clinician.

Immunocompromised patients

Adhere strictly to aseptic technique. Skin disinfection contact time matters more here than anywhere else.

Patients refusing the draw

A patient can withdraw consent at any time. Stop, document, and notify the requesting clinician.

Safety and the phlebotomist

Phlebotomy puts the worker at risk of bloodborne pathogen exposure. Standard precautions assume every patient is potentially infectious:

• Gloves, and gowns/eye protection where splash is possible
• Single-use, safety-engineered sharps
• Never recap needles
• Immediate sharps disposal in a puncture-resistant container

If you sustain a needlestick

1. Wash the area with soap and running water. Do not squeeze the wound as this can drive contaminants deeper.
2. Report the injury immediately to your supervisor and occupational health.
3. Test the source patient (with consent) for HIV, hepatitis B, and hepatitis C.
4. Consider HIV post-exposure prophylaxis within hours if the source is high-risk.
5. Check your hepatitis B vaccination status and arrange follow-up serology per local protocol.

Quality assurance

Reliable results depend on systems, not just individuals. Good phlebotomy services maintain:

• Standardized labeling and barcode verification
• Documented order of draw on every collection chart
• Routine audits of hemolysis and rejection rates
• Calibrated equipment and stocked, in-date supplies
• Training and recertification for every phlebotomist

How many attempts is too many?

Not more than two venipuncture attempts is the most common standard [1]. After two unsuccessful tries, hand the patient over to a more experienced colleague. Repeated sticks increase the risk of nerve injury, hematoma, and patient refusal of future care.

Frequently Asked Questions (FAQs)

What is the difference between phlebotomy and venipuncture?

Phlebotomy is the whole practice of drawing blood for testing or treatment, including patient preparation, sample collection, labeling, and disposal. Venipuncture is one specific technique within phlebotomy — inserting a needle into a vein, usually in the arm, to draw a sample. A finger or heel prick is also phlebotomy, but it is not venipuncture.

Why does the order in which blood tubes are filled matter?

Each tube contains a different additive. If a small amount of additive carries over into the next tube, it changes the chemistry of that sample and produces wrong results. The CLSI PRE02 (2025) sequence — blood culture first, then light blue citrate, red or gold serum, green heparin, lavender EDTA, and gray fluoride last — is designed to prevent this carryover [2].

How many times can a phlebotomist try to draw blood?

The widely accepted standard is no more than two attempts by the same phlebotomist. If both fail, another phlebotomist can try twice more, then a senior clinician should be involved. The goal is not a fixed number but knowing when to stop, because repeated attempts increase the risk of nerve injury, hematoma, and patient distress.

What is the most common reason a blood sample is rejected by the lab?

Hemolysis or the rupture of red blood cells is the leading cause of rejected hematology and chemistry samples. It is usually caused by vigorous shaking, too small a needle, prolonged tourniquet time, or pulling a syringe plunger too hard. Most hemolysis is preventable with good technique.

Why is the median cubital vein preferred?

It is usually large and stable, sits close to the surface in the middle of the antecubital fossa, and is separated from the brachial artery and median nerve by a fibrous sheet called the bicipital aponeurosis. That separation makes it the safest vein to puncture. The basilic vein, on the inner side, lies right next to the median nerve and brachial artery and is avoided when possible.

What should I do if I get a needlestick injury during phlebotomy?

Wash the area with soap and running water immediately. Do not squeeze the wound. Report the injury to your supervisor and occupational health. Source-test the patient with consent for HIV, hepatitis B, and hepatitis C. HIV post-exposure prophylaxis should be considered within hours for high-risk exposures. Document the incident and arrange follow-up serology.

Glossary of Related Medical Terms

• Antecubital fossa — The shallow triangular area on the front of the elbow where the most common veins for blood draw sit just under the skin.
• Anticoagulant — A chemical added to a blood tube that stops the sample from clotting so cells or plasma can be tested.
• Bevel — The slanted, sharpened tip of a needle. The angled side should face up during insertion.
• Capillary puncture — A small skin prick (usually on a finger, heel, or earlobe) used to collect a tiny blood sample.
• CLSI — Clinical and Laboratory Standards Institute, a U.S.-based body that publishes international laboratory standards including GP41 for venipuncture.
• Evacuated tube — A blood collection tube with a pre-set vacuum that pulls a measured volume of blood when connected to the needle.
• Hemoconcentration — A falsely raised concentration of cells and large molecules caused by fluid shifting out of the vein, often from leaving a tourniquet on too long.
• Hemolysis — Rupture of red blood cells, which spills their contents into the plasma and ruins many test results.
• Hematoma — A bruise-like collection of blood that has leaked out of a vein into the surrounding tissue.
• Median cubital vein — The preferred vein for venipuncture in the antecubital fossa because it is large, stable, and sits away from major nerves and arteries.
• Order of draw — The standardized sequence for filling blood tubes during a single venipuncture, designed to prevent additive carryover between tubes.
• Phlebotomy — The practice of drawing blood, whether for testing (diagnostic) or as a treatment (therapeutic).
• Pre-analytical phase — Everything that happens before a sample is tested: ordering, collection, labeling, transport, and storage. Most laboratory errors occur here.
• Tourniquet — An elastic band tightened around the upper arm to make veins easier to find and puncture.
• Vasovagal reaction — A reflex that drops heart rate and blood pressure in response to stress, sometimes causing fainting during a blood draw.
• Venipuncture — Puncturing a vein with a needle to draw blood. It is one technique within the broader practice of phlebotomy.

Disclaimer: This protocol is for educational purposes only. Local laboratory standard operating procedures take precedence. It is not intended to be a substitute for informed professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for clinical decision-making. While the information presented here is derived from credible medical sources and is believed to be accurate and up-to-date, it is not guaranteed to be complete or error-free. See additional information.

References

1. WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy. Geneva: World Health Organization; 2010. 2, Best practices in phlebotomy. Available from: https://www.ncbi.nlm.nih.gov/books/NBK138665/
2. Clinical and Laboratory Standards Institute. (2025). Collection of diagnostic venous blood specimens (8th ed., CLSI standard PRE02). Wayne, PA: CLSI.
3. Simundic, A. M., Bölenius, K., Cadamuro, J., Church, S., Cornes, M. P., van Dongen-Lases, E. C., Eker, P., Erdeljanovic, T., Grankvist, K., Guimaraes, J. T., Hoke, R., Ibarz, M., Ivanov, H., Kovalevskaya, S., Kristensen, G. B. B., Lima-Oliveira, G., Lippi, G., von Meyer, A., Nybo, M., De la Salle, B., … Working Group for Preanalytical Phase (WG-PRE), of the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) and Latin American Working Group for Preanalytical Phase (WG-PRE-LATAM) of the Latin America Confederation of Clinical Biochemistry (COLABIOCLI) (2018). Joint EFLM-COLABIOCLI Recommendation for venous blood sampling. Clinical chemistry and laboratory medicine, 56(12), 2015–2038. https://doi.org/10.1515/cclm-2018-0602
4. Lippi, G., Salvagno, G. L., Montagnana, M., Franchini, M., & Guidi, G. C. (2006). Phlebotomy issues and quality improvement in results of laboratory testing. Clinical laboratory, 52(5-6), 217–230.
5. Plebani M. (2010). The detection and prevention of errors in laboratory medicine. Annals of clinical biochemistry, 47(Pt 2), 101–110. https://doi.org/10.1258/acb.2009.009222