Which of the following can cause a hematoma to form as a result of a blood draw?

When you get a blood test, it's possible that you could be left with a bruise. Learn how it can happen, and what to do if it does.

How Blood is Drawn

If your doctor orders a blood sample, your blood will be collected by either a doctor, nurse, or phlebotomist. That's someone who's specially trained to collect blood samples.‌

First, the person taking your blood will place a tourniquet around your arm above where your elbow sits. This helps your veins become easier to see and work with. 

Then they'll clean and disinfect the area on the inside of your elbow. After that, a small needle gets placed into your arm. Once the needle is in your arm, samples of your blood will be collected in small vials or bottles.

Next, they will take the needle out of your arm and apply pressure with a gauze or a cotton ball over the spot where the needle was inserted. They'll ask you to keep applying pressure until the area stops bleeding, and then they will put a clean bandage over it.

If You Get a Bruise

Getting blood drawn is a simple process, but the most common complication associated with it is bruising. Your doctor might call this kind of bruise is also called a hematoma. That's a swollen area filled with blood.

A hematoma that you get after a blood test often looks more serious than it is. Over the following days, the blood inside the hematoma will absorb back into your body. The blood that surfaces closest to the skin is what causes its purple appearance. As the days pass, the bruise will fade in color, turning yellow or green until it eventually disappears.

To help your bruise heal properly, you can:

• Leave the bandage on for at least 8 hours.
• Avoid lifting anything heavy with the affected arm for a few hours.
• Avoid taking aspirin or ibuprofen for the next 72 hours.
• Put an ice pack or cold compress to the affected area for about 20 minutes, a few times during the first 24 hours after you have blood drawn.
• Switch from an ice pack to a warm compress for the second 24 hours after your blood is drawn. Apply it to the affected area for 20 minutes a few times throughout the day.

When to Call Your Doctor

You should seek medical attention if:

• Your swelling gets noticeably worse.
• Your hand changes color or feels numb
• You feel throbbing or intense pain.