Phlebotomy, the process of drawing blood, is a routine medical procedure performed millions of times daily for diagnostic testing or donation. A common outcome is the development of a hematoma at the puncture site. This occurs when blood leaks from the punctured vein into the surrounding tissue, creating a visible, localized collection of blood. Understanding the mechanisms and factors that contribute to this leakage helps explain why this complication happens.
Understanding Hematomas After a Blood Draw
A hematoma is a collection of clotted blood that forms outside of a blood vessel. Unlike a simple bruise (ecchymosis), a true hematoma often presents as a raised, tender lump alongside skin discoloration. This lump is a pocket of blood that has escaped the vein and pooled in the soft tissues beneath the skin.
The hematoma forms when the vein wall is temporarily compromised by the needle during the blood draw. If the small puncture hole does not seal immediately after the needle is removed, blood pressure within the vein forces blood out. This extravasated blood then accumulates in the surrounding connective tissue. This accumulation leads to the characteristic swelling and purple-blue discoloration.
Causes Related to Phlebotomy Procedure and Technique
One of the most frequent mechanical reasons for hematoma formation is the needle passing completely through the vein wall, a mishap known as transfixing the vein. This action creates two holes instead of one. Blood can leak from the second, unpressurized exit point into the tissue behind the vein. The leakage starts immediately because the vein cannot seal both entry and exit points at the same time.
Improper needle placement, such as inserting the needle too shallowly or at an incorrect angle, can also lead to issues. If the needle partially enters the vein, it can scrape or lacerate the inner vessel wall, causing trauma. Movement of the needle during the draw, often called “fishing,” further damages the vein wall and surrounding capillaries. This increases the likelihood of blood escaping the intended vessel.
The size of the needle used relative to the patient’s vein diameter plays a role in the extent of the defect left behind. A larger gauge needle creates a bigger hole in the vein wall, which requires more time and pressure to properly seal. Furthermore, inadequate or delayed pressure application after the needle is withdrawn is a significant contributor. This failure allows blood flow out of the puncture site before a natural clot can form.
The phlebotomist must release the tourniquet before removing the needle from the arm. If the needle is removed while the tourniquet is still constricting the limb, the increased pressure within the vein immediately forces blood out through the fresh puncture site. This rapid leakage under pressure quickly forms a substantial hematoma.
Patient-Specific Factors That Increase Risk
Certain pre-existing conditions or treatments can make a patient inherently more susceptible to developing a hematoma after a blood draw.
Medication Use
Patients taking anticoagulant medications, such as Warfarin or direct-acting oral anticoagulants (DOACs), or antiplatelet drugs like aspirin, have a significantly impaired ability to form a clot quickly. This prolonged clotting time means the vein puncture site remains open and prone to leakage for a longer duration.
Vein Fragility
Vein integrity naturally diminishes with age, making veins more fragile and susceptible to tearing or leakage upon puncture. Older adults and individuals on long-term steroid therapy often have less supportive tissue and thinner, more delicate vessel walls. These fragile veins may not withstand the pressure of the blood draw or the minor trauma of the needle insertion.
Patient Movement and Hydration
Movement or muscle tension by the patient during the procedure can cause the needle to shift within the vein, creating a larger tear or puncture. Other underlying conditions that impair the body’s natural coagulation cascade, such as specific clotting factor deficiencies, also predispose the patient to subcutaneous bleeding. Proper hydration is another factor, as well-hydrated patients tend to have fuller, easier-to-access veins, reducing the need for needle adjustments.
Immediate Care and Future Prevention
Once a hematoma begins to form, immediate and firm pressure must be applied directly to the site to physically compress the vein and stop the internal bleeding. Applying a cold compress or ice pack to the affected area within the first 24 hours helps to constrict blood vessels. This limits the size of the collection and reduces swelling. The affected limb should be elevated, and the patient should rest the area to prevent further trauma.
A typical hematoma resolves on its own as the body reabsorbs the pooled blood, usually fading over one to two weeks. For future prevention, patients should inform the phlebotomist about any blood-thinning medications and ensure they are well-hydrated before the appointment. After the procedure, apply firm, direct pressure to the puncture site for several minutes, avoiding bending the elbow.
While most hematomas are benign, severe or worsening pain, numbness, tingling in the hand, or signs of infection like increasing warmth or discharge require prompt medical attention.