Causes of Blood Clots in the Arm

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

This lesson is going to cover some of the most common causes of blood clots that appear normally and abnormally in the arm. We will discuss how each cause leads to blood clot formation.

Blood Clots

Can you imagine how our lives would go if blood clots didn't form in our bodies? Most of us would have been in some serious trouble before the age of ten. That's because we need blood clots to form in order to stop us from bleeding when we injure ourselves. Life could have been a wrap the first time you fell off of your bike without the ability to form blood clots!

While we definitely need blood clots to form, we need them to form at the right time and in the right place. When they form any other time or place, then the body may suffer and it could cost us our lives. There are two different types of blood clots that can form in the body. A thrombus is a blood clot in a blood vessel that isn't moving around. An embolus is a blood clot that has broken free from where it formed and entered the bloodstream.

There are quite a few different reasons why blood clots appear in different places in the body. One place in the body where both a thrombus and embolus may occur is in the arm. Let's look at what causes blood clots in the arm.

Causes of Blood Clots in the Arm


A very common cause of blood clots in the arm is simply not moving the arm. Aside from just not exercising much, immobility of the arm could be due to injury, surgery, or paralysis. The link between the arm not moving and blood clots may not be apparent, so let's look closer. The muscles inside of the arm contract to move the arm. When they contract, they also squeeze on the blood vessels within the arm, which helps to keep blood moving at the normal speed through the arm. Without the help of the muscles, the blood moves slower and slow-moving blood is more likely to form blood clots.

Excess Blood Clotting Factors

During Pregnancy

The next cause may be something that you have experienced or heard about, but didn't fully understand. Pregnancy is a cause of blood clots in the arm. Sounds crazy, right? Not so much.

Pregnancy can cause blood clots in the arm
Picture of a pregnant woman

The body anticipates that there will be a sizable amount of blood lost during delivery, so more blood clotting factors are produced in the blood to help ensure the mom won't bleed out from giving birth. The accumulation of blood clotting factors could cause the blood to form clots in the arm when it doesn't need to.

From Birth Control Pills

The same thing happens when a woman takes estrogen-based birth control pills since they trick the body into thinking that it is pregnant. The increased level of estrogen increases the amount of clotting factors and blood clots can form in her arm.

At Other Times

Outside of pregnancy, there are times when the composition of the blood may just contain more blood clotting factors than it is supposed to. The same result happens in this situation as with pregnancy. More blood clotting factors, more chances for blood clots in the arm.

Heart Function

Problems with the functioning of the heart could also create blood clots in the arm. The heart must be able to pump blood efficiently enough for it to circulate through the entire body and come back to the heart. When the heart is not working right, blood tends to not move at the desired speed, and this can causes the blood to clot. One of the likely places that the blood will clot in is the arm.


Another possible cause of blood clots in the arm is atherosclerosis. This is the narrowing of a blood vessel due to the build-up of plaque and inflammation inside it.

Blood clots are likely with atherosclerosis
Diagram of atherosclerosis

This narrowing decreases the amount of space that blood has to flow through and therefore, the blood gets backed up and flows slower. What did we just say happens when blood moves slowly? It forms clots! Atherosclerosis in the blood vessels of the arm would cause blood clots to form in the arm.

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