What is the Difference Between Primary Polycythemia and Secondary Polycythemia

The key difference between primary polycythemia and secondary polycythemia is that primary polycythemia is the increase in red blood cells due to abnormalities in red blood cell production, while secondary polycythemia is the increase in red blood cells due to factors such as hypoxia, sleep apnea, certain tumours, or high level of erythropoietin hormone, etc.

Polycythemia refers to an increase in the number of red blood cells in the body. These extra red blood cells cause blood to be thicker. This increases the risk of other health issues such as blood clots. Polycythemia is divided into two main categories as primary polycythemia and secondary polycythemia.

1. Overview and Key Difference
2. What is Primary Polycythemia
3. What is Secondary Polycythemia
4. Similarity – Primary Polycythemia and Secondary Polycythemia
5. Primary Polycythemia vs Secondary Polycythemia in Tabular Form
6. Summary – Primary Polycythemia vs Secondary Polycythemia

What is Primary Polycythemia?

Primary polycythemia is an increase in red blood cell count due to abnormalities in red blood cell production. Normally, primary polycythemia is due to factors intrinsic to red blood cell precursors. It is also called polycythemia vera, polycythemia rubra vera or erythremia. This condition occurs when excess red blood cells are produced due to an abnormality of the bone marrow. In this condition, in addition to red blood cells, white blood cells and platelets are also produced.

Primary Polycythemia vs Secondary Polycythemia in Tabular Form

Figure 01: Blood Smear Taken from a Patient having Primary Polycythemia

Primary polycythemia is a myeloproliferative disease. Myeloproliferative disease is a rare blood cancer in which excess red blood cells, white blood cells or platelets are produced in the bone marrow. The symptoms include headache, vertigo, enlarged spleen or liver, high blood pressure and formation of blood clots. The transformation of this condition to acute leukaemia is rare. The mainstay of the treatment is phlebotomy. Furthermore, primary familial polycythemia is a benign hereditary condition. It is due to an autosomal dominant mutation in the erythropoietin receptor gene (EPOR). This hereditary polycythemia can increase up to 50% oxygen-carrying capacity of the blood.

What is Secondary Polycythemia?

Secondary polycythemia is an increase in red blood cell count due to factors such as hypoxia, sleep apnea, certain tumours, or a high level of erythropoietin hormone. Secondary polycythemia means that some other condition is causing the body to produce too many red blood cells. Normally, there is a high level of erythropoietin hormone naturally or artificially in secondary polycythemia that drives the production of red blood cells. The secondary polycythemia in which the production of erythropoietin hormone increases is called physiologic polycythemia.

Primary Polycythemia and Secondary Polycythemia - Side by Side Comparison

Figure 02: Composition of Blood

In addition to breathing obstructions such as sleep apnea, lung disease, heart disease, tumours (neoplasms), performance-enhancing drugs may also cause secondary polycythemia. In secondary polycythemia, 6 to 8 million erythrocytes can occur per cubic millimetre of blood. The symptoms include fatigue, headache, dizziness, blurred vision, anorexia, weakness, and reduced mental acuity. Heritable cause of secondary polycythemia is associated with abnormalities in haemoglobin oxygen release. People who have the special haemoglobin Hb Chesapeake usually suffer from secondary polycythemia. The treatment options for this condition include low dose aspirin or bloodletting.

Similarities Between Primary Polycythemia and Secondary Polycythaemia

Primary polycythemia and secondary polycythemia are two types of absolute polycythemia.
In both types of polycythaemias, the number of red blood cells is high.
Both types can be inherited.
They can occur due to tumours.
Both types can be treated through phlebotomy.

Difference Between Primary Polycythemia and Secondary Polycythaemia

Primary polycythemia occurs due to abnormalities in red blood cell production, while secondary polycythemia occurs due to factors such as hypoxia, sleep apnea, certain tumours, or a high level of erythropoietin hormone. So, this is the key difference between primary polycythemia and secondary polycythemia. Furthermore, in primary polycythemia, the red blood cell count will be high, but the level of erythropoietin will be low. On the other hand, in secondary polycythemia, both the red blood cell count and the level of erythropoietin will be high.

The following infographic lists the differences between primary polycythemia and secondary polycythemia in tabular form for side by side comparison.

Summary – Primary Polycythemia vs Secondary Polycythaemia

Polycythemia is a rare disorder caused due to an increase in the number of red blood cells in the body. Primary polycythemia and secondary polycythemia are two types of absolute polycythemia. Primary polycythemia happens due to abnormalities in red blood cell production, while secondary polycythemia happens due to factors such as hypoxia, sleep apnea, certain tumours, or a high level of erythropoietin hormone. Thus, this is the key difference between primary polycythemia and secondary polycythemia.

Reference:

1. “Polycythaemia” Nhs Choices, NHS.
2. Hecht, Marjorie. “Secondary Polycythemia: Causes, Treatment, Symptoms, and More.” Healthline, Healthline Media, 8 Feb. 2019.

Image Courtesy:

1. “Polycythemia vera, blood smear” By The Armed Forces Institute of Pathology (AFIP) (Public Domain) via Commons Wikimedia
2. “1901 Composition of Blood” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia

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