Polycythemia: Definition & Causes

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  • 1:26 Polycythemia Vera
  • 2:34 Secondary Polycythemia
  • 4:55 Symptoms
  • 6:00 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Polycythemia is a blood disorder in which the body produces too many blood cells as a result of a problem with the bone marrow or an increased production of the hormone erythropoietin. Learn about the causes of polycythemia.


If you are even a casual fan of professional sports, you have probably heard about an athlete who was fined or kicked out of their sport due to blood doping. When an athlete 'dopes' their blood, what they are really doing is injecting themselves with extra blood or a substance that increases the number of oxygen-carrying red blood cells in their body. With more oxygen comes more endurance and an unfair edge over their competition.

From a health standpoint, this is not such a great idea because the athlete is actually creating a blood condition known as polycythemia, which is a blood disorder in which there are too many red blood cells. These extra cells thicken the blood, making a person more prone to blood clots, which in turn heightens their risk of heart attack or stroke. While blood doping is a deliberate act, there are other causes of polycythemia that are due to underlying conditions or factors. These causes will be the focus of this lesson.

We mentioned that polycythemia is a disorder that results in too many red blood cells. This is a fairly easy term to remember if you break the term down into its parts. For instance, we see that the prefix 'poly' means many, the word 'cyt' refers to cells and the suffix 'emia' refers to in the blood. So polycythemia is literally 'many cells in the blood.'

Types: Polycythemia Vera

There are two types of polycythemia. The first is called polycythemia vera, which is also known as primary polycythemia. Polycythemia vera is caused by a problem with the bone marrow, resulting in an overproduction of cells. The bone marrow is the 'primary' site for red blood cell production, which might help you recall this term's alternate name. This is also the site where white blood cells and platelets are made, and in a person with polycythemia vera, we see that all of these cells may increase. You might want to use this fact to help you recall this type, because in polycythemia vera there are 'very' many cells.

In a person with polycythemia vera, the overproduction of cells appears to be due to a gene mutation involving the JAK2 gene. This gene makes a protein that helps in the production of blood cells. Now being a gene problem, you might think this is an inherited disorder, but this is not the case with polycythemia vera, and in fact, the reason for this change in the gene is not known.

Types: Secondary Polycythemia

The second type of polycythemia is conveniently called secondary polycythemia. It is caused by an increased production of erythropoietin, resulting in an overproduction of red blood cells. Erythropoietin is a hormone produced in the kidneys that increases red blood cell production when oxygen levels are low.

Erythropoietin stimulates the bone marrow, so for red cells to be produced, we first need working bone marrow, and secondly we need erythropoietin. You might want to recall this fact to help you remember the importance of erythropoietin in secondary polycythemia.

Erythropoietin is produced in response to a lack of oxygen. If you think about it, this is a pretty ingenious move by your body because red blood cells are responsible for circulating oxygen. So, if the level of oxygen is low, your body squirts out more erythropoietin to make more red blood cells. These extra red cells then grab a hold of and circulate more of the oxygen that is available. It's almost as if the body is making more workers to get the job done.

The interesting thing about secondary polycythemia is that for a person living at a high altitude, this increased production of erythropoietin can be a normal adaptation to their environment. In fact, this is why we see elite athletes training in high-altitude locations. The 'thin air' gives them an oxygen-carrying edge and improves their stamina, somewhat like a legal form of blood doping.

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