A butterfly needle is a device used to access a vein for drawing blood or giving medications.

Some medical professionals call a butterfly needle a “winged infusion set” or a “scalp vein set.” The set gets its name because there are plastic “wings” on either side of a hollow needle used to access the vein.

While some elements of the butterfly needle can vary, most have a needle in a winged sheath or plastic covering that’s pulled back to reveal the needle. The needle is attached to tubing that may have a luer lock. This is a type of connection that you can twist a syringe onto.

butterfly needleShare on Pinterest
Butterfly needle sets are small, flexible devices that are used to access superficial veins for blood draw or intravenous injections. Photo via Getty images.

A medical professional will use a butterfly needle to draw your blood or to try and access a vein to give intravenous (IV) medications.

Alternatively, they may use an intravenous catheter. It has a retractable needle that’s inside a protective sheath. The needle is inserted into the vein, and then a button is pushed to retract the needle and leave the sheath or catheter.

This is different from a butterfly needle, where the needle gets left in the vein instead of a plastic sheath. However, the butterfly needle is usually smaller in length than an IV catheter.

There are certain cases where one should be chosen over the other. Drawing blood is one of these cases.

A person drawing blood may choose a butterfly needle when drawing blood for the following purposes:

Venipuncture

A venipuncture is when a phlebotomist accesses a vein to draw blood. A phlebotomist is a medical professional who specializes in drawing blood.

Butterfly needles are often used on people who might be difficult to perform venipuncture on. These include:

  • older adults
  • infants
  • children
  • people who are “difficult sticks”

The butterfly needle requires a shallower angle compared to an IV catheter. The smaller-length needle is easier to place more precisely on veins that are especially fragile, small in size, or that roll.

Butterfly needles are often used when a person is giving blood, such as for a blood bank. The needle has flexible tubing attached to the end that makes it easy to connect to other tubing to collect blood.

IV hydration

If you need IV fluids, a nurse or doctor may use a butterfly needle to access a vein. IV hydration may be used to treat dehydration or if you’re unable to eat or drink due to illness or a pending surgery.

The hollow butterfly needle allows IV fluids to be infused to help rehydrate you and restore your fluid levels.

Medication

A butterfly needle also allows a doctor to give IV medications. These medications can be “pushed” through a syringe. Getting them through a vein is helpful when you can’t take medications by mouth or you need the medications to work quickly.

Butterfly needles usually aren’t a long-term solution to IV therapy, such as giving medications or fluids. This is because the needle can easily become displaced from the vein. A doctor may suggest IV access through a bigger vein via a central line or peripherally inserted central catheter (PICC) line.

Manufacturers make butterfly needles in a variety of sizes. They’re measured by gauges. Most butterfly needles range from 18 to 27 gauge. The higher the number is, the smaller or thinner the needle size is.

While the size can vary, most needle sizes are 21 to 23 gauge. If a person uses the smaller-sized needles (such as 25 to 27 gauge), blood is more likely to get destroyed (hemolyze) or clot due to the smaller-sized needle.

A 2016 study found that using butterfly needles to draw blood reduced rates of blood breaking down by half compared to using a person’s IV catheter to draw a blood sample.

Another earlier study found the type of needle used was one of the strongest predictors that a blood sample would or wouldn’t get destroyed. The researchers found that using butterfly needles was less associated with causing blood breakdown when compared with IV catheters.

Using the butterfly needle may also have more advantages for those with bleeding disorders, such as hemophilia or von Willebrand disease.

Butterfly needles enable IV access using a small needle for IV infusions or blood draws. Ideally, using a butterfly needle reduces the likelihood a person will experience profuse bleeding after an IV stick or blood draw.

Butterfly needles used for IV medications or fluids involve leaving an actual needle in the vein. On the other hand, an IV catheter is a thin, flexible catheter with no needle on the end. Leaving a needle in could potentially injure a part of the vein or nearby areas if accidentally removed.

While the amount of time a butterfly needle can be used for medications or fluid administration may vary based on the manufacturer, some manufacturers recommend an infusion of no more than five hours with a butterfly needle.

Sometimes, butterfly needles can be difficult to insert properly. The short needle may be easily pulled back from the vein, and you may require another stick.

To prevent unintended sticks, some butterfly needles have a “push-button” function that retracts the needle when the blood draw is complete. Sometimes it’s possible to push this button before intended.

A butterfly needle may make the blood test process easier if you have veins that are typically very tough to access or have a medical condition that may cause you to bleed more than is typical.

These needles are very helpful for people who traditionally have veins that are hard to find, collapsible, or small. With the right practitioner, butterfly needles can make blood draws a generally easy and fairly painless process.