Even when you follow proper technique, things go wrong during blood draws. A patient moves, a vein rolls, or an underlying condition you did not know about causes unexpected bleeding. Knowing how to recognize and respond to complications is a core clinical skill — and it is tested directly on the NHA CPT exam through scenario-based questions.
This article walks through each major complication: what causes it, how to recognize it, and exactly what to do. Learn these well. The exam will put you in a situation and ask what you do next.
Hematoma
A hematoma is a localized collection of blood that pools under the skin, forming a bruise or a visible swelling at the puncture site. It is the most common phlebotomy complication.
What causes it
- Through-and-through needle placement — the needle passes completely through the vein, allowing blood to leak into surrounding tissue from the back wall
- Removing the tourniquet after the needle is withdrawn — or more accurately, failing to remove the tourniquet before needle withdrawal. When venous pressure is still elevated at the moment of withdrawal, blood is pushed out through the puncture hole
- Insufficient post-draw pressure — not holding firm pressure long enough, or the patient bending their arm at the elbow (which opens the vein rather than compressing it)
- Needle partially out of the vein — angle too steep or bevel partially outside the lumen causes blood to track alongside the needle into tissue
Prevention
Always release the tourniquet before withdrawing the needle. Apply direct pressure immediately after needle removal — with the arm extended, not bent. Hold for at least two minutes, longer for patients on anticoagulants. Use the correct needle gauge and angle for the vein you selected.
Response
If you see the site swelling during the draw, remove the needle immediately, apply firm pressure, and elevate the arm. Do not continue attempting to draw from that site. Document what happened. If the hematoma is large or the patient reports significant pain, notify the nurse or ordering provider.
Syncope (Fainting)
Syncope — fainting or near-fainting — happens when a patient experiences a vasovagal response. Blood pressure drops, blood flow to the brain decreases briefly, and the patient loses or nearly loses consciousness. It can happen before, during, or after the draw.
Warning signs
Watch for these early signs, especially in patients who tell you they have fainted before:
- Sudden pallor (skin turns pale or gray)
- Diaphoresis (sweating, often cold and clammy)
- Patient reports dizziness, lightheadedness, or nausea
- Yawning or sighing repeatedly
- Eyes glazing over or patient becoming unresponsive to conversation
Response
If a patient shows any of these signs, stop the draw immediately and remove the needle. Lower the patient's head below their heart — recline the chair if it is adjustable, or have the patient lower their head between their knees if seated upright. Apply a cold, damp compress to the forehead or back of the neck.
Ammonia inhalants (smelling salts) are only appropriate if the patient is actually unconscious and your facility protocol permits their use. Do not use them on a conscious patient. Talk to the patient calmly and keep them in place until they feel fully recovered.
Never leave a syncopal patient alone. Stay with them, call for help if needed, and document the episode. A patient who feels fine may still faint if they stand up too quickly — make sure they sit for several minutes before getting up.
If the patient is in a standard chair (not a draw chair with arms), position them on the floor or in a safer position before they fall. Preventing a fall injury is the immediate priority.
Nerve Injury
Nerves run close to the veins in the antecubital fossa. The median nerve and its branches are at greatest risk, particularly when drawing from the median cubital vein or when probing with the needle.
How to recognize it
The patient will report a sudden sharp or shooting pain that radiates down the arm, into the hand, or into the fingers. Tingling or an electric sensation is also a common description. This is different from the normal brief sting of venipuncture.
Response
Stop the draw immediately if the patient reports shooting pain, electric sensations, or tingling that radiates beyond the puncture site. Remove the needle without redirecting it. Do not attempt to angle or reposition while the needle is in tissue — this is a common way nerve injuries occur in the first place.
Apologize to the patient, apply pressure, and document the complaint. Nerve injuries from phlebotomy are usually transient, but the patient should be told to report any persistent numbness or weakness to their provider.
Never redirect a needle if the patient is reporting pain beyond the normal stick. The NHA CPT exam treats this as a clear stop condition.
Petechiae
Petechiae are tiny, pinpoint red or purple spots that appear on the skin under or near the tourniquet. They look like a fine red rash or a cluster of small dots.
They form when capillaries rupture under the pressure of the tourniquet. Petechiae are more common when the tourniquet is left on too long (over one minute), applied too tightly, or when the patient has an underlying coagulation disorder or fragile capillaries.
When you see petechiae, remove the tourniquet, complete or discontinue the draw, and document the finding. Petechiae themselves do not require emergency treatment, but their presence may signal a problem with the patient's platelet function or clotting. The ordering provider should be made aware, especially if the petechiae are widespread or the patient has no prior history of them.
On the exam, petechiae questions often test whether you know the cause (tourniquet pressure or coagulation disorder) versus confusing them with other skin findings.
Excessive Bleeding
Most puncture sites stop bleeding within a minute or two with normal pressure. Excessive bleeding is when the site continues to bleed beyond two to three minutes despite sustained pressure.
Common causes
- Patient is taking anticoagulants (warfarin, heparin, rivaroxaban, apixaban) or antiplatelet medications (aspirin, clopidogrel)
- Undiagnosed or known bleeding disorder (hemophilia, von Willebrand disease, thrombocytopenia)
- Liver disease, which reduces clotting factor production
Response
Apply firm, continuous pressure for a minimum of five minutes without lifting to check. Checking early releases the pressure and restarts the clotting process. If bleeding continues after five minutes, maintain pressure and notify nursing staff. Do not leave the patient until the site has stopped bleeding or someone else takes over.
Before the draw, ask about blood thinners. This is a standard pre-draw patient assessment question and it directly affects your post-draw protocol.
Allergic Reactions
Latex allergy
Latex allergy can range from contact dermatitis (redness, itching at the skin contact area) to a systemic anaphylactic reaction in severe cases. Always ask patients about latex allergy before starting. Use nitrile gloves as your standard practice — most facilities have moved to nitrile already, but confirm before you draw.
Signs of a systemic reaction include hives beyond the contact area, wheezing, swelling of the lips or throat, or a sudden drop in blood pressure. This is a medical emergency. Remove the source, call for help immediately, and stay with the patient.
Adhesive sensitivity
Some patients react to the adhesive in bandages, developing redness or a raised rash under and around the bandage. Ask about adhesive sensitivity before applying. Paper tape or a self-adherent wrap are alternatives. If a reaction develops after the patient has left, they should be directed to remove the bandage and wash the area.
Collapsed Vein
A collapsed vein occurs when the vein walls are pulled inward and collapse under the vacuum pressure of the collection tube. The vein stops yielding blood partway through the draw, or you get no blood at all despite correct needle placement.
This is more common with:
- Small or fragile veins (elderly patients, patients with a history of IV drug use)
- Using a tube with too strong a vacuum for the vein size
- Pulling back on a syringe plunger too forcefully
Response
Switch to a smaller-volume tube, which has less vacuum. Alternatively, use a syringe and draw back slowly rather than relying on vacuum at all. A butterfly (winged infusion) set can also help because it allows more control over flow rate. If the vein collapses completely, withdraw and attempt a different site.
Vigorous probing to find the vein again after collapse causes tissue damage and increases the risk of hematoma and nerve injury. If the site is not working, move on.
Infection
Infection at a venipuncture site is rare when proper technique is followed. Standard precautions — hand hygiene, gloves, and a 70% isopropyl alcohol prep with 30 seconds of drying time — are highly effective at preventing site contamination.
Signs to watch for
The patient will not show signs of infection during the draw. Infection develops over hours to days. Signs include increasing redness or warmth at the site, swelling, purulent discharge, and fever. Phlebitis (inflammation of the vein) may develop if contamination occurs.
If a patient calls or returns reporting these signs after a draw, they should be directed to their provider. Document all draws accurately so the site and time can be identified.
Your role in infection prevention is technical: clean technique, proper prep, no touch after prep, and correct disposal of sharps. There is no shortcut in this area.
How the NHA CPT Tests Complications
The NHA CPT exam does not ask you to list complications. It puts you in a scenario — "during a draw the patient says her arm is tingling and shooting pain goes to her fingers, what do you do?" — and tests whether you know the correct immediate action. For every complication above, know: (1) how to recognize it, (2) what to do first, and (3) what to document. That pattern covers the vast majority of complication questions you will see.
Practice Questions
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During a venipuncture, you notice the puncture site beginning to swell. What is the correct first action?
- A. Apply the tourniquet more tightly to control bleeding
- B. Remove the needle immediately and apply direct pressure
- C. Switch to a larger gauge needle to complete the draw faster
- D. Continue the draw and apply pressure after tube collection is complete
Answer: B. A swelling site indicates hematoma formation. Remove the needle immediately and apply direct, firm pressure. Continuing the draw or delaying withdrawal makes the hematoma larger.
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A patient becomes pale and reports feeling dizzy partway through a blood draw. After removing the needle, what should you do next?
- A. Administer an ammonia inhalant immediately
- B. Have the patient stand up and walk to increase circulation
- C. Lower the patient's head and apply a cold compress
- D. Leave the patient briefly to get help from the nursing station
Answer: C. These are classic signs of vasovagal syncope. Lower the head and apply a cold compress to the forehead or neck. Ammonia inhalants are only used for unconscious patients per most protocols. Never leave the patient alone.
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Midway through drawing a CBC, the patient says she feels a sharp, shooting pain going down her forearm into her fingers. You have good blood return. What should you do?
- A. Complete the draw quickly since you already have needle placement
- B. Redirect the needle slightly toward the vein center
- C. Remove the needle immediately and do not redirect
- D. Reduce the vacuum by switching to a smaller tube
Answer: C. Shooting or electric pain radiating down the arm indicates nerve contact. Stop and remove the needle immediately. Do not redirect — redirecting is a primary cause of nerve injury. Document the complaint.
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After a draw, you apply pressure and release it after 90 seconds. The site is still bleeding. The patient mentions she takes warfarin daily. What is the appropriate next step?
- A. Reinsert the needle to release the clot that may be blocking the site
- B. Apply pressure for at least five minutes without releasing to check
- C. Apply a tight pressure bandage and discharge the patient
- D. Document the bleeding and move on since anticoagulants always cause this
Answer: B. Anticoagulants impair clotting. Apply firm, continuous pressure for a minimum of five minutes without interruption. Releasing pressure early restarts the process. Do not discharge until the site is controlled.
Summary
Complications happen even with good technique. What separates a skilled phlebotomist is knowing the signs early and responding correctly — not panicking, not continuing when you should stop, and not leaving a patient alone when something goes wrong.
The pattern for the exam is simple: recognize the complication, take the correct immediate action, document it. Know that pattern cold for hematoma, syncope, nerve injury, petechiae, excessive bleeding, allergic reactions, collapsed veins, and infection. You will see at least two or three scenario questions from this content on the NHA CPT.