Venipuncture, commonly known as a blood draw, is a routine medical procedure involving the puncture of a vein to obtain a blood sample. This technique is primarily used for diagnostic laboratory testing, therapeutic monitoring, or blood donation. Although venipuncture is performed frequently, it carries risks. Healthcare professionals must be aware of specific circumstances where a venipuncture attempt should be avoided to prevent complications, ensure patient safety, and maintain the integrity of the collected specimen.
Localized Conditions and Anatomical Restrictions
The condition of the skin and underlying tissue at the intended puncture site can prohibit a safe blood draw. Areas exhibiting active infection, such as cellulitis or an abscess, must be avoided to prevent introducing surface bacteria directly into the bloodstream, which can lead to a systemic infection. Additionally, a vein that feels hard or cord-like may be sclerosed from repeated punctures or inflammation, making it difficult to access and potentially painful.
Drawing blood from a site with extensive scarring, such as from burns or surgical procedures, is generally contraindicated. Scar tissue is difficult to penetrate, and underlying veins may be displaced or compromised, increasing the risk of painful, failed attempts. Similarly, a site with edema, or swelling, should be bypassed because the accumulated tissue fluid can dilute the blood sample, leading to inaccurate test results.
If an existing hematoma, a localized collection of clotted blood, is present, venipuncture near or through it should be avoided. Puncturing the area can cause additional bleeding, lead to further expansion, and potentially contaminate the sample with clotted or hemolyzed blood, which may alter laboratory values. The only acceptable alternative on that extremity is a site distal to the hematoma, meaning further down the limb.
Specialized vascular access sites are a paramount concern and must not be used for routine blood draws. This includes an arm containing an arteriovenous (AV) fistula or graft, which is surgically created for hemodialysis patients to ensure high-flow access. Puncturing these sites risks damaging the access, leading to clotting, infection, or loss of access necessary for the patient’s dialysis treatment.
Systemic Medical Risks and Patient History
A patient’s medical history and systemic condition can introduce risks requiring careful site selection or the avoidance of venipuncture. Individuals with coagulation disorders, such as hemophilia, or those on high-dose anticoagulant medications face an increased risk of excessive bleeding and large hematoma formation. For these patients, prolonged pressure must be applied to the site, and the draw should be performed only when necessary.
Venipuncture is traditionally avoided on the arm of a patient who has undergone a mastectomy with lymph node removal. This precaution is taken because puncturing the skin in a limb with compromised lymphatic drainage can trigger or exacerbate lymphedema, a chronic swelling of the arm. Although current evidence suggests the risk may be lower than historically believed, avoiding the ipsilateral arm remains the standard safety protocol, especially if the patient has a history of lymphedema.
When a patient requires frequent blood sampling or high-volume draws, a strategy is employed to conserve viable veins. This involves rotating sites and avoiding veins that are best preserved for future procedures, such as the large median cubital vein, to ensure long-term venous access is maintained. Avoiding a site in this context is a long-term strategy for patient care, not due to an immediate risk.
When Procedural Safety or Sample Integrity is Compromised
Circumstances arising during the procedure can compromise the accuracy of test results or pose a threat to the patient’s well-being. Drawing a sample from a vein located proximal, or above, an active intravenous (IV) line infusion must be avoided. The infusate, which may be saline, glucose, or medication, will flow downward and mix with the blood sample, causing dilution or contamination that renders the test results inaccurate.
If a different site cannot be used, the IV infusion must be paused for a minimum of two minutes. The first few milliliters of blood drawn must then be discarded to clear the line before the sample is collected. Patient safety is a major concern, especially for individuals with a history of fainting (syncope) or extreme needle anxiety. These patients should be positioned lying down, and the draw must be immediately stopped if they report symptoms like dizziness or nausea.
Unsuccessful venipuncture attempts should be limited to a maximum of two times before stopping the procedure. Continuing to probe after multiple failures increases the patient’s pain, causes unnecessary tissue trauma, and raises the likelihood of nerve injury or hematoma formation. If two attempts fail, a different, more experienced phlebotomist should be called, or an alternative collection method, such as a capillary stick, should be considered.
Special precautions are necessary when collecting blood from newborns and infants due to their small size. Deep venipuncture should be avoided in these patients to prevent injury to nearby nerves, arteries, or bones. Instead, the preferred method is a superficial collection from the heel, which is a safer way to obtain the small sample volume required for most neonatal tests.