A hematoma is a localized collection of blood outside of blood vessels, commonly appearing as a bruise. During a blood draw (phlebotomy), a hematoma forms when blood leaks from the punctured vein and collects in the surrounding tissues. This is a common, typically minor, and temporary complication. Understanding how and why hematomas develop can help in their prevention and management.
How Hematomas Form
During phlebotomy, a needle creates a small opening in the vein for blood collection. A hematoma forms when blood escapes this puncture site and accumulates under the skin. This leakage can occur if the vein is punctured completely through, or if insufficient pressure is applied to the site immediately after needle withdrawal. The visible discoloration is pooled blood trapped beneath the skin.
Factors That Increase Hematoma Risk
Several factors can increase the likelihood of a hematoma forming after a blood draw, including patient-specific conditions and procedural aspects. Certain medications, such as anticoagulants (warfarin, heparin) and antiplatelet drugs (aspirin, clopidogrel), significantly heighten bleeding risk. Patients on these medications are more prone to hematoma formation, even from minor vessel injury.
Patient-related factors include vein condition; older adults often have fragile veins susceptible to leakage. Some individuals have “rolling veins” that shift easily or deep veins challenging to access, increasing trauma risk. Underlying health conditions, like inherited coagulation disorders (hemophilia, von Willebrand disease) or acquired issues (liver disease, vitamin K deficiency), impair clotting, leading to easier bruising. Patient movement during the draw can also dislodge the needle, causing additional vein trauma.
Procedural elements related to the phlebotomy technique also contribute to hematoma risk. Improper needle insertion, such as inserting the needle too deeply, going completely through the vein, or using an incorrect angle, can cause blood to leak. Multiple attempts to find a vein also increase the likelihood of damaging surrounding capillaries and causing blood leakage. Using a needle size that is too large for a patient’s vein can create a larger hole that is more difficult for the body to seal effectively. Additionally, inadequate pressure applied to the puncture site immediately after the needle is removed allows blood to continue seeping out of the vein.
Preventing Hematomas
Preventing hematomas involves a combination of patient awareness and careful phlebotomy technique. Patients should inform the healthcare professional about any medications they are taking, especially blood thinners or antiplatelet drugs, before the blood draw. Remaining still and relaxed during the procedure minimizes accidental needle movement and potential vein trauma. After the needle is removed, applying firm and continuous pressure directly to the puncture site for at least two to five minutes is important. Avoiding heavy lifting or strenuous activity with the affected arm for several hours post-draw helps maintain the clot and prevent re-bleeding.
Healthcare professionals also play a significant role. Selecting an appropriate vein, choosing the correct needle size, and ensuring a single, clean venipuncture minimizes vessel trauma. Releasing the tourniquet before withdrawing the needle reduces vein pressure, decreasing blood leakage. Providing clear instructions to the patient on how to apply pressure and care for the site afterwards is also a preventive measure.
Managing a Hematoma
If a hematoma does occur, several steps can help manage it and promote healing. Immediately, apply a cold compress or ice pack to the affected area for 10-20 minutes at a time, several times during the first 24-48 hours, to reduce swelling and restrict further blood leakage. After 24-48 hours, switch to a warm compress to promote reabsorption of pooled blood.
Elevating the affected arm, if possible, above heart level can also help reduce swelling. Over-the-counter pain relievers such as acetaminophen can alleviate discomfort; however, nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen should be avoided if the patient is on blood thinners, as they can increase bleeding risk. Most hematomas resolve naturally within one to two weeks, gradually changing color from dark blue or purple to green and yellow as the body reabsorbs the blood. Medical attention should be sought if the hematoma is excessively large, very painful, rapidly expanding, accompanied by numbness or tingling in the limb, or shows signs of infection such as increased redness, warmth, pus, or fever.