Several complications can arise during venipuncture, and prompt recognition and response are essential. A hematoma is a localized collection of blood under the skin, essentially a bruise, caused by blood leaking from the vein during or after puncture. Hematomas commonly result from excessive probing, the needle passing entirely through the vein, insufficient pressure after the draw, or use of a needle that is too large for the vein. If a hematoma begins to form during the draw, the phlebotomist should immediately release the tourniquet, remove the needle, and apply firm pressure to the site. Drawing from an arm with an existing hematoma is avoided because the specimen can be altered and additional bruising or pain can result.
Hemolysis, the rupture of red blood cells and release of intracellular contents such as potassium, can produce falsely elevated results for several analytes and turns the serum or plasma a pink or red tinge. Common causes of hemolysis include using a needle that is too small in gauge, vigorous mixing of the specimen, drawing blood through an existing IV line, pulling back too forcefully on a syringe plunger, and partially filling a tube so that the additive-to-blood ratio is incorrect. Drawing from an edematous arm can also cause contamination of the specimen with tissue fluid, producing inaccurate results.
Nerve injury is among the more serious complications of venipuncture, and the median, radial, and ulnar nerves of the antecubital region are at greatest risk, particularly when puncture is attempted near the basilic vein. Signs of nerve injury include sharp, shooting pain, tingling, numbness, or an electric shock sensation radiating down the arm. If a patient reports any of these symptoms during the draw, the phlebotomist must stop the procedure immediately and remove the needle. Iatrogenic nerve injury refers specifically to nerve damage caused by a medical procedure such as improper needle placement. Probing or excessive redirecting of the needle markedly increases the risk of nerve injury, hematoma, and patient discomfort.
Other complications to recognize include thrombophlebitis, or inflammation of a vein with clot formation, which can result from repeated venipuncture at the same site, and petechiae, which are tiny red spots caused by capillary bleeding under the skin and may indicate an underlying bleeding or clotting disorder. Vasovagal syncope is a fainting response triggered by anxiety or pain that causes a drop in heart rate and blood pressure; if a patient becomes faint or begins to faint, the phlebotomist should stop the draw, lower the patient's head or have them lie down, apply a cold compress, and monitor the patient closely. Allergic reactions may also occur, including reactions to latex in gloves or tourniquets or to adhesives and antiseptics. Drawing above an existing IV line should be avoided because IV fluids can dilute or contaminate the specimen, producing inaccurate results.