What Are the Side Effects of Getting Blood Drawn?

Most people who get blood drawn walk away with nothing more than a small bandage and mild soreness at the puncture site. The procedure is one of the most common in medicine, and serious complications are genuinely rare. But “rare” does not mean nonexistent, and even the minor side effects are worth understanding so you know what is normal, what deserves a phone call to your doctor, and what you can do to reduce your risk.

Bruising Is the Most Common Aftereffect

A bruise at the puncture site is the single most frequent side effect of venipuncture. It happens when a small amount of blood leaks from the vein into the surrounding tissue, producing a discolored, sometimes tender patch that can range from the size of a thumbprint to a few inches across. Bruises from blood draws typically change color over a few days and clear up within one to two weeks without any treatment.

You are more likely to bruise if you take blood-thinning medications like aspirin or warfarin, if you have a clotting disorder, or if you did not press firmly enough on the site after the needle was removed. Older adults tend to bruise more easily because the skin and blood vessels become more fragile with age. One study of elderly patients found that venipuncture-induced hematomas can even temporarily alter the skin’s moisture-retention function in the area around the puncture, suggesting the trauma extends slightly beyond what is visible on the surface.¹ Applying steady pressure for at least five minutes after the draw and keeping the bandage on for a few hours helps minimize bruising.

Fainting and Lightheadedness

Feeling dizzy or actually passing out during or shortly after a blood draw is called a vasovagal response. Your nervous system overreacts to the stress of the needle, blood pressure drops, heart rate slows, and the brain briefly does not get enough blood flow. It can happen whether you are watching the needle or looking away. Symptoms range from mild wooziness and clammy skin to a full loss of consciousness.

A large Japanese study tracking nearly 678,000 phlebotomy patients found that vasovagal syncope occurred in about 0.004% of draws, so the absolute numbers are very low. But the study also revealed patterns worth knowing. About 70% of the patients who fainted were female, and the median age was 23, meaning younger adults were more susceptible. More than half of those who fainted were having blood drawn at that facility for the first time, suggesting that unfamiliarity with the setting plays a role. The number of tubes collected also mattered: the odds of fainting were roughly eight times higher when five or more tubes were needed compared to just three.²

If you have a history of fainting during blood draws, let the phlebotomist know beforehand. Lying down rather than sitting upright during the draw, staying well hydrated, and eating something before your appointment all help. Most labs will let you rest in the chair for as long as you need afterward.

Nerve Injury

The inside of the elbow, the most common site for blood draws, has several superficial nerves running close to the veins. Occasionally the needle grazes or directly contacts one of these nerves, causing sharp, shooting, or electric-shock-like pain that radiates down the forearm or into the hand. This is different from the normal brief sting of the needle entering the skin.

In most cases the discomfort is fleeting and resolves within seconds. Rarely, it can persist as tingling, numbness, or burning that lasts days to weeks. A case report involving two patients who sustained injury to the lateral antebrachial cutaneous nerve during venipuncture found that both achieved full recovery after ultrasound-guided nerve blocks and oral medication.³ Persistent nerve symptoms beyond a few days warrant medical attention, because early treatment tends to produce better outcomes. The risk is hard to eliminate entirely since the exact position of these small nerve branches varies from person to person and they are not visible through the skin.

Rare Vascular Complications

The veins targeted during a standard blood draw sit close to arteries in some people, and occasionally the needle enters an artery by mistake. You will usually know if this happens because arterial blood is bright red and may pulse into the collection tube, while venous blood is darker and flows steadily. An accidental arterial puncture can lead to a hematoma that is larger and more painful than a typical venous bruise, and in very rare cases it can cause temporary vessel occlusion or a pseudoaneurysm, which is a contained bulge in the artery wall.⁴

Even rarer is a true aneurysm of the brachial artery following blood donation. Case reports document that accidental arterial injury during venipuncture can lead to localized thrombosis and, in exceptional circumstances, aneurysm formation.⁵ Similarly, there are case reports of superficial venous thrombophlebitis progressing into deeper veins after a routine blood draw.⁶ These scenarios are genuinely unusual, but they underline why you should seek medical advice if you notice a growing, pulsating, or increasingly painful lump at the site days after a blood draw, or if the arm becomes swollen and red along the path of the vein.

Anxiety and Needle Phobia

The psychological side effects of blood draws are underappreciated. An international survey of over 2,000 adults found that roughly 63% reported some degree of needle phobia, with the average fear rating falling at about 5.7 on a 10-point scale. The most commonly cited reasons were general anxiety and anticipated pain. Among those who reported needle fear, more than half said they had avoided blood draws, and about a third had skipped vaccinations because of it.⁷

This matters because avoiding routine blood work can delay diagnosis of conditions like diabetes, thyroid disease, or kidney problems. If anxiety around needles leads you to cancel or postpone lab orders, it is worth discussing with your doctor. Techniques that help include applied muscle tension (repeatedly tensing your leg and arm muscles to keep blood pressure up, which also counters the vasovagal response), controlled breathing, and distraction methods like listening to music or watching a video during the draw. Some clinics offer topical numbing agents as well. For severe phobia, cognitive behavioral therapy has strong evidence of effectiveness.

Pain During the Draw

Some discomfort during venipuncture is expected, but the amount of pain varies a lot based on factors you might not think about. Age is one: children tend to report higher pain scores, partly because of smaller veins and partly because of fear amplifying the sensation.⁸ The phlebotomist’s skill matters, too. A smooth, confident first stick tends to hurt less than multiple attempts to find a vein.

Site selection plays a role. The antecubital fossa (the inside of the elbow) generally hurts less than the back of the hand because the veins there are larger and surrounded by more tissue. If you consistently have painful draws, ask whether a butterfly needle, which is smaller and more maneuverable, is an option. In pediatric settings, needle-free lidocaine delivery systems have been tested and shown to provide rapid analgesia when applied one to three minutes before the stick.⁹ For adults, over-the-counter topical lidocaine creams can be applied about 30 minutes before the appointment, though you should check with the lab beforehand since some discourage it.

Allergic Reactions at the Puncture Site

Itchy, red, or blistering skin around the bandage area after a blood draw sometimes has nothing to do with the needle itself. The adhesive in the tape, the antiseptic used to clean the skin, or the materials in the dressing can trigger contact dermatitis. One reported case involved a blood donor who developed an itchy, vesicular rash precisely in the area where a chlorhexidine-alcohol antiseptic dressing was applied; patch testing confirmed that the chlorhexidine was the allergen.¹⁰ Latex allergies can also cause reactions if the phlebotomist uses latex gloves or a latex tourniquet, though most facilities have switched to latex-free alternatives.

If you know you react to adhesives or specific antiseptics, mention it before the draw begins. Alternatives such as paper tape, self-adherent wrap, or alcohol-free antiseptics are widely available. A reaction limited to the tape site that resolves within a few days is typically a contact sensitivity rather than a sign of infection, but spreading redness, warmth, swelling, or streaking along the vein warrants prompt medical evaluation.

When Repeated Blood Draws Cause Anemia

A single blood draw removes only a few milliliters and has no meaningful effect on your blood counts. But for hospitalized patients who have blood drawn daily or even multiple times a day, the cumulative loss adds up. This is sometimes called iatrogenic anemia, meaning anemia caused by the medical care itself.

A study of patients admitted to an internal medicine service found that the average volume of blood collected during a hospital stay was about 75 mL. After adjusting for other factors, every 100 mL of blood drawn was associated with a hemoglobin drop of about 7 g/L.¹¹ In intensive care units, the volumes are even higher. One case series found that ICU patients had a median of about 143 mL of blood collected per week, and by the eighth day of the stay, 80% of the patients in the study had anemia, up from 67% at admission.¹²

This is primarily a concern for people who are already in the hospital, especially those with long stays or pre-existing anemia. If you are having routine outpatient blood work a few times a year, the volume drawn is trivially small relative to your total blood supply and your body replaces it quickly. But if you are a patient or a caregiver for someone undergoing frequent blood draws during a prolonged hospitalization, it is reasonable to ask the care team whether all ordered labs are truly necessary.

Blood Draws in Children

Everything that applies to adults also applies to children, but with a few amplified dimensions. Fear is the big one. Children are more likely to be overwhelmed by the unfamiliar clinical environment, less able to hold still, and more prone to associating the experience with pain on future visits. The presence of a child life specialist during the draw has been shown to make a meaningful difference. In one study, children who had a specialist present spent a median of three minutes in the procedure room instead of five, and the proportion requiring physical restraint by two or more people dropped from 84% to 52%. Self-reported fear also roughly halved.¹³

Technology-based distraction is another promising approach. A randomized controlled trial testing tablet-based augmented reality during venipuncture in children found that the AR groups had significantly lower anxiety, fear, and pain scores compared to children who received standard care, as reported by the children themselves, their parents, and the nurses.¹⁴ If your child needs regular blood work, asking the lab whether they have distraction tools, child life support, or topical numbing options can make the experience significantly less distressing for everyone involved.

Finger Pricks Versus Vein Draws

Some tests can be done with a capillary sample from a fingertip rather than a venous draw from the arm. This is common for blood glucose checks and certain point-of-care tests. From a side-effect standpoint, capillary sampling tends to produce less anxiety and fewer symptoms overall. A cohort study comparing hypodermic needles and safety lancets found that symptoms like dizziness and distress were significantly lower with lancets, and the sight of others being pricked was far less anxiety-inducing when lancets were used instead of conventional needles.¹⁵

The trade-off is that capillary blood is not suitable for many tests. It can be affected by how hard the finger is squeezed, by contamination with tissue fluid, and by temperature differences in the hand. For comprehensive panels, cultures, or tests requiring larger volumes, venipuncture remains the standard. But if the test you need can be done either way, and needles are a significant source of anxiety for you, it is worth asking whether a finger prick is an option.

Infection at the Puncture Site

Infection after a routine blood draw is exceedingly uncommon when standard sterile technique is followed. The skin is cleaned with an antiseptic before the needle goes in, and the needle itself is sterile and single-use. Still, any break in the skin creates a theoretical entry point for bacteria. Signs of infection include increasing redness, warmth, swelling, pus, or a fever developing in the hours to days after the draw. This is more of a concern for people who are immunocompromised or have conditions that impair wound healing, such as poorly controlled diabetes. If you notice any of these signs, contact your healthcare provider rather than assuming it is a normal bruise.

How to Reduce Your Risk of Side Effects

Most side effects from blood draws are either very mild or very rare, and a few simple steps lower the odds of even the common ones:

Stay hydrated: Drinking water before your appointment plumps your veins, making them easier to find and reducing the chance of multiple needle sticks.
Eat something: Unless your test requires fasting, having a meal beforehand helps stabilize blood sugar and reduces the likelihood of feeling lightheaded.
Speak up: Tell the phlebotomist if you have fainted before, if you have allergies to latex or adhesives, or if one arm tends to have better veins than the other.
Apply pressure: After the needle is removed, press a cotton ball or gauze firmly over the site for at least five minutes without peeking. Bending the elbow is less effective than direct flat pressure.
Skip heavy lifting: Avoid strenuous use of the arm for a few hours afterward. Carrying heavy grocery bags or doing a bicep workout right after a draw increases the chance of a larger bruise.

People on anticoagulants may need to hold pressure for ten minutes or longer. If you are on blood thinners and notice a bruise that keeps expanding rather than stabilizing over the first day, let your doctor know.