Polycythemia: Types & Diagnosis

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Too much blood? Sounds strange, right? This lesson will explore what happens when a person has too many red blood cells, or polycythemia, and will also look at different types of this disease as well as ways in which it is diagnosed.

What is Polycythemia

Have you ever heard of anyone having too much blood? Sounds weird, doesn't it? Polycythemia is just that. Specifically, it is when a person's bone marrow makes too many red blood cells (RBCs), the cells that deliver oxygen to tissues in the body. Bone marrow is found inside of the bones, as depicted in the following image. The bone marrow makes more RBCs when the hormone, erythropoietin, is secreted by the kidneys and liver in response to low levels of oxygen in the body.

The red portion is the bone marrow
bm1

The word polycythemia might not sound like 'too much blood', but it actually means just that. 'Poly' means many, 'cyte' means cell and 'hemia' is a condition having to do with blood. If RBCs carry oxygen to tissues, it doesn't seem like you can have too many. It seems like the more you have, the more oxygen your tissues get, right? Unfortunately no. It's a case of too much of a good thing and it can cause problems! When a person's body makes too many RBCs, they sort of 'clog up' the system, resulting in less oxygen being delivered to the body's tissues, and that's no good. Let's take a look at the two main types of polycythemia : primary polycythemia and secondary polycythemia.

Primary Polycythemia

Primary Polycythemia is when the body makes too many RBCs and is usually due to a mutation in a gene. Primary polycythemia includes:

  • Polycythemia vera (PV)
  • Primary familial and congenital polycythemia (PFCP)

Polycythemia vera (PV) is very rare and, in addition to RBCs, an increase in white blood cells and platelets can be observed as well as low erythropoietin levels in the blood. It wasn't until 2005 when researchers identified a gene mutation as the cause of PV. Scientists believe that this mutation makes the body more sensitive to erythropoietin, thus increasing the number of RBCs produced by the body. This disorder is more prevalent in white males and usually starts to show up around 40-50 years of age.

The gene associated with PV is found on chromosome 9
geg

The second type of primary polycythemia, primary familial and congenital polycythemia (PFCP), is also the result of a separate mutation that also increases the body's sensitivity to erythropoietin, thus resulting in the production of too many RBCs. Like PV, this condition is very rare.

Secondary Polycythemia

In secondary polycythemia, the body produces too many RBCs due to an increase in erythropoietin. Remember, the body makes erythropoietin when it detects there's not enough oxygen being delivered to the tissues. Secondary polycythemia is caused when there isn't enough oxygen being delivered, or when there is a tumor that results in an increased output of erythropoietin. Let's look at both possibilities.

  • Chronic hypoxia is when the tissues are not getting enough oxygen due to an underlying cause like heart or lung problems.
  • The second cause are tumors that can actually cause the body to make more erythropoietin. Since erythropoietin is increased, the bone marrow responds by increasing the amount of RBCs produced.

Diagnosis

There are many tests that are conducted when doctors are trying to diagnose polycythemia. Below are some of the tests along with a brief description of when polycythemia is suspected.

  • Blood tests
    • Doctors will look at the following: the hematocrit, or the amount of RBCs found in the blood compared to the total amount of blood; the amount of hemoglobin, the protein associated with RBCs; and the amount of erythropoietin. If the hematocrit and hemoglobin are elevated, polycythemia is suspected. If erythropoietin is low, PV is suspected and if it's high, secondary polycythemia is suspected.
  • Biopsy
    • Doctors may perform a bone marrow biopsy, where a sample of the bone marrow is taken. If it is found that the bone marrow is making too many RBCs, polycythemia is suspected.
  • Genetic tests
    • If primary polycythemia is suspected, doctors may look for genetic mutations in the genes associated with the production of RBCs.
  • Other tests
    • If secondary polycythemia is suspected, doctors will look at chest x-rays and EKGs to see if the lungs or heart are limiting the amount of oxygen that is getting to tissues.

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