Platelet Counts in Rheumatoid Arthritis

Elevated Platelet Not Uncommon With Inflammatory Conditions

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What Are Platelets?

Platelets are small circulating cell fragments that play a significant role in hemostasis (the process of stopping bleeding after injury). Platelets do not have a nucleus but do contain cytoplasm and proteins important for platelet function. Platelets are produced by megakaryocytes in the bone marrow. The condition of elevated platelets is known as thrombocytosis. Platelets are often elevated in rheumatoid arthritis.

In rheumatoid arthritis, the joints are the primary site of damage. That is where local inflammation occurs, involving blood cells which include neutrophils and macrophages. Those cells also stimulate the production of platelet activating factor, which in turn cause the accumulation of blood platelets, allowing them to participate in an inflammatory response in the body.

Platelets in Rheumatoid Arthritis

Healthy people have a platelet count in the normal range of 150,000-400,000/mm3. As long ago as 1972, in was noted in medical literature that researchers (Selroos et al.) found elevated platelet counts in approximately one-third of rheumatoid arthritis patients. It was found to be directly associated with disease activity. Selroos also found a correlation between the elevated platelet count and anemia, leucocytosis (increased number of white blood cells), and rheumatoid factor. There is an inverse relationship between hemoglobin and platelet count, meaning, when hemoglobin is low, the platelet count is high.

The association of sideropenia (iron deficiency) and platelet count elevation was not found to be significant.

Some patients with severe rheumatoid arthritis  may have platelet counts over a million. When the disease is brought under control with medications, the platelet count typically returns to normal.

Platelets are elevated not only in rheumatoid arthritis, but also in other similar inflammatory condition.

A significant correlation was found between elevated platelets and cutaneous vasculitis. Other extraarticular manifestations of rheumatoid arthritis (i.e., beyond just the joints) were found more often among patients with elevated platelet counts. 

What Causes Elevated Platelet Counts in Rheumatoid Arthritis?

The best explanation for elevated platelet counts in rheumatoid arthritis appears to be related to chronic anemia, a common characteristic of rheumatoid arthritis. According to the Annals of the Rheumatic Diseases (1976), platelet homeostasis is controlled by thrombopoietin. Thrombopoietin is the major regulator of megakaryocyte growth and differentiation. It is thought that thrombopoietin may be related chemically to erythropoietin (a hormone involved in red blood cell production), largely because chronically anemic patients with reticulocytosis (increased number of immature red blood cells) and increased erythropoietin levels have higher than normal platelet counts.

If erythropoietin levels are increased in anemic rheumatoid arthritis patients, elevated platelet counts could result.

Another possibility would be if increased platelet production was caused by increased platelet destruction or consumption. Researchers also proposed that elevated platelet counts may be connected to immunological responses in rheumatoid arthritis -- perhaps as a consequence of small clots within chronically inflamed synovium

According to Kelley's Textbook of Rheumatology, there are three main causes for elevated platelet counts in rheumatic diseases:

  • reactive thrombocytosis, secondary to the chronic inflammatory process. In such cases, cytokines (IL-1, IL-6, and TNF) may be active mediators in the regulation of platelet production during an inflammatory process.
  • familial thrombocytosis may occur due to an inherited gene mutation.
  • clonal thrombocytosis (primary or essential thrombocytosis) is an unregulated abnormality of platelet production due to sustained megakaryocyte proliferation.


Thrombocytosis in rheumatoid arthritis. Hutchinson RM et al. Annals of the Rheumatic Diseases. (1976)35:138

Bloodstream thrombopoietin in rheumatoid arthritis with thrombocytosis, Kiraz S. et al. Clinical Rheumatology. 2002 Nov; 21(6):453-6.

Kelley's Textbook of Rheumatology. Ninth Edition. Chapter 17. Platelets and Rheumatic Diseases. Pages 249-251.

Scandinavian Journal of Rheumatology. Selroos, O. 1972 1:136. Thrombocytes in Rheumatoid Arthritis.

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