A bruise may appear after a blood draw if small blood vessels get damaged when the needle gets inserted or if there isn’t enough pressure applied after the needle is removed.

Bruising after a blood draw is typically harmless and doesn’t require treatment. But, if your bruises are large or accompanied by bleeding elsewhere, it could be a sign of a more serious condition.

Bruising, also known as ecchymosis, happens when capillaries located just under the skin are damaged, leading to bleeding just underneath the skin. The bruise itself is discoloration from the blood trapped under the skin’s surface.

Damaging blood vessels

During a blood draw, a healthcare provider specially trained to collect blood — most likely a phlebotomist or a nurse — inserts a needle into a vein, usually on the inside of your elbow or wrist.

As the needle is inserted, it may damage a few capillaries, leading to the formation of a bruise. This isn’t necessarily the fault of the person drawing the blood as it’s not always possible to see these small blood vessels.

It’s also possible that the needle needs to be repositioned after the initial placement. The person drawing the blood may also insert the needle too far beyond the vein.

Small and hard-to-find veins

If the person drawing blood has any difficulty locating a vein — for example, if your arm is swollen or your veins are less visible — it makes it more likely that blood vessels will be damaged. This may be referred to as “a difficult stick.”

The person drawing the blood will usually take the time to locate the best vein, but sometimes they aren’t successful on the first try.

Not enough pressure after

Another reason a bruise may form is if the person drawing the blood doesn’t apply enough pressure on the puncture site once the needle is removed. In this case, there’s more of a chance that blood will leak into the surrounding tissues.

Other causes of bruising after blood draws

You might be more prone to bruising during or after a blood draw if you:

Older adults may also bruise more easily as their skin is thinner and has less fat to guard the blood vessels from injury.

If a bruise forms after a blood draw, it’s usually not a cause for concern. However, if you notice bruising on other parts of your body or the bruise is very large, you may have another condition that could explain the bruising.

You can’t always avoid bruising after a blood draw. Some people just tend to bruise more easily than others.

If you’re scheduled to have blood drawn, there are a few steps you can try to prevent a bruise:

  • Avoid taking anything that can cause blood thinning in the days before your appointment and 24 hours after the blood draw, including over-the-counter NSAIDs.
  • Don’t carry anything heavy, including a handbag, using that arm for several hours after the blood draw, since lifting heavy objects can put pressure on the needle site and displace your blood clot.
  • Wear a top with loose-fitting sleeves during the blood draw.
  • Apply firm pressure once the needle is removed and keep your bandage on for a few hours after the blood draw.
  • If you notice a bruise forming, apply a cold compress to the area of injection and elevate your arm to help speed up the healing process.

You should tell your doctor and the person drawing blood if you bruise frequently from having blood taken. Be sure to also tell them if you have any medical conditions or you’re taking any medications known to cause issues with clotting.

Butterfly needles for blood collection

If you notice that the person drawing the blood is having a difficult time locating a good vein for a blood draw, you can request the use of another type of needle called a butterfly needle, also known as a winged infusion set or a scalp vein set.

Butterfly needles are often used to draw blood in infants, children, and older adults. A butterfly needle requires a shallower angle and is a shorter-length, making it easier to place in small or fragile veins. This reduces the likelihood you’ll bleed and bruise after a blood draw.

It’s important to know, however, that healthcare providers who draw blood are encouraged to use traditional methods before the use of butterfly needles, due to the risk of clotting.

If you ask for a butterfly needle, there’s a chance your request may not be granted. It may also take longer to draw blood using a butterfly needle because it’s smaller or finer than the standard needle.

If the bruise is large, or you notice that you bruise easily, it could indicate an underlying condition, such as a clotting problem or a blood disease. On top of bruising after a blood draw, you should see your doctor if you:

  • often experience large bruises that can’t be explained
  • have a history of significant bleeding, such as during surgery
  • suddenly begin bruising after you start a new medication
  • have a family history of bruising or bleeding episodes
  • are experiencing unusual bleeding in other places, such as your nose, gums, urine, or stool
  • have severe pain, inflammation, or swelling at the site of the blood draw
  • develop a lump at the site where blood was drawn

Bruises after a blood draw are fairly common and will go away on their own as the body reabsorbs the blood. The bruise is caused by damage to a few small blood vessels during the blood draw process, and is usually not the fault of your healthcare provider.

The bruise may change in color from dark blue-purple, to green, and then brown to light yellow over the course of a week or two before it goes away completely.