Thrombocytopenia overview

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Associate Editor-In-Chief: Farbod Zahedi Tajrishi, M.D. [2]

Thrombocytopenia (or -paenia, or thrombopenia in short) is the presence of relatively few platelets in blood.

Generally speaking, a normal platelet count ranges from 150,000 and 450,000 per mm³. These limits, however, are determined by the 2.5th lower and upper percentile, and a deviation does not necessarily imply any form of disease. The number of platelets in a blood sample also decreases quickly with time and a low platelet count may be caused by a delay between sampling and analysis.

Thrombocytopenia can be divided into several categories based on its extent as well as its underlying etiology.

Based on platelet count:

• mild: (100,000 – 150,000 per µL),
• moderate (50,000 to 99,000 per µL),
• severe (<50,000 per µL).

Note that these amounts may not be the same for every condition and one should interpreted them according to the underlying etiology of thrombocytopenia. For example, in idiopathic thrombocytopenia (ITP), a platelet count of <30,000/µL represents severe thrombocytopenia and for gestational thrombocytopenia, a platelet count between 80,000 and 150,000/microL is considered as mild thrombocytopenia.

Based on etiology:

To see the full list of conditions that could cause thrombocytopenia, please click here.

Basically, thrombocytopenia is the result of one of these mechanisms or a combination of some of them:

1. Reduced production of platelets due to bone marrow dysfunction
2. Increased destruction of platelets in the body
3. iatrogenic
4. entrapment of platelets in spleen

Several conditions, some of which mentioned below, can activate the mechanisms that ultimately lead to thrombocytopenia.

Among people with normal platelet counts:^[1][2]

• The mean platelet count is 266,000/µL in women and 237,000/µL in men.

• Younger people and those with African-Americans descent have higher platelet counts than the older ones and caucasians, respectively.

• The variation of the platelet count in a given individual over a certain time course is insignificant.
• Platelet counts are slightly higher (by approximately 5000/µL) in the fall/winter compared with spring/summer.

• Almost 2.5 percent of the normal population have platelet counts lower than 150,000/µL.

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