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What Are the Common Causes of Blood Not Clotting?

By Meshell Powell
Updated Mar 03, 2024
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Problems with clotting can be caused by a variety of factors and is known medically as coagulopathy. Inherited medical disorders such as hemophilia are among the most common reasons for blood not clotting as it should. Other possible causes include liver disorders, certain forms of cancer, or long-term use of some types of medication. Symptoms which may indicate that there is a problem with blood clotting properly may include weakness, dizziness, excessive bleeding when receiving a minor cut, or blood in the stool or vomit.

Hemophilia is an inherited medical disorder which leads to the blood not clotting normally. This condition causes excessive bleeding after any injury which breaks the skin. Internal bleeding may also occur as a result of hemophilia. Without immediate treatment, hemophilia can become life-threatening. For reasons which are not completely understood, this disorder primarily affects males, with very few exceptions.

Liver disorders can sometimes lead to problems with clotting. Hepatitis and cirrhosis of the liver are the most common liver disorders which may lead to this symptom. Hepatitis is a type of infection involving the liver, while cirrhosis leads to the development of severe scar tissue.

Some forms of cancer carry a risk of causing complications such as the blood not clotting as it should. This is particularly common in cancers which spread to the liver, including pancreatic, colon, and breast cancer. Blood cancers such as lymphoma or leukemia may also have this effect on the blood.

Long-term use of some prescription medications may eventually lead to the blood not clotting normally. Medications known as anticoagulants are designed to thin the blood, and prolonged usage may prevent the blood's ability to clot. Some of the stronger antibiotics may also have this effect. Those taking these types of medications may be advised to have periodic blood tests to make sure this complication does not develop.

Any symptoms which indicate that the blood may not be clotting as well as it should needs to be reported to a doctor for further evaluation. These symptoms often include a feeling of weakness or dizziness along with unexpected bruising or difficulty in getting a cut to stop bleeding. Bowel movements which are dark black or red should definitely be reported to a doctor, as internal bleeding may be present. Blood in the urine or dark vomit which resembles coffee grounds may sometimes indicate a clotting problem as well.

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Discussion Comments
By Ana1234 — On Mar 17, 2013

I've always been worried I would be teaching children who had an undiagnosed blood disorder that makes it so that their blood does not clot.

I can't imagine anything scarier than not being able to help someone while they keep bleeding. At least if you're forewarned, you can call the ambulance right away, but there is such a fine line between life and death for kids and if you don't know beforehand that they have this kind of trouble, you might not make the right decision.

By MrsPramm — On Mar 17, 2013

@pleonasm - I hope you also encouraged him to go and get a check up just in case it was something else wrong. It's well known that certain medications can "thin the blood". That's why people at risk of heart attack (who don't have blood clotting disorders, of course) are encouraged to take aspirin every day, so that they are less likely to develop an internal clot.

By pleonasm — On Mar 16, 2013

Even some common medications can lead to the blood not clotting properly. You have to be very careful about this kind of thing.

My father was often taking cold and flu medication to make sure he was able to go to school even when he wasn't feeling well (he was a high school teacher). One night while I was visiting, he had just had a tooth extracted and the stitches started bleeding and wouldn't stop.

He didn't wake me up, unfortunately, or I would have taken him to the hospital but just sat and applied pressure and waited for the blood to stop (which, thank goodness, it did eventually).

We realized later that it was the cold medication that had thinned his blood and made it so that it wouldn't stop coming from the stitches.

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