Platelets

Platelets



Basic Information image



Definition




• Thrombocytopenia/thrombopenia: Low number of circulating platelets


• Thrombocytosis/thrombocythemia: Increased number of circulating platelets


• Thrombopathia/thrombocytopathia: Abnormal platelet function, often in the presence of a normal platelet number



Typical Normal Range (US Units; SI Units)


117,000 to 256,000/µL with no reported variation between breeds



Physiology


Platelets are made by megakaryocytes in the bone marrow, spleen, and lung. They are small, anuclear, discoid fragments of megakaryocyte cytoplasm that are sheared off during thrombopoiesis, rather than formed through stepwise mitosis. Their main function is in primary hemostasis, where they adhere to the site of vascular injury through interaction with von Willebrand factor (vWF) and various glycoprotein receptors. Once initial adhesion occurs, platelets bridge fibrinogen via exposed GP IIb-IIIa receptors and form a platelet plug. After the platelet plug is formed, a conformational change occurs, causing release of the platelet α and β granules, which contain various vasoactive compounds, clotting factors, and cytokines, thus promoting both the clotting and inflammatory cascades. As they also release numerous growth factors, platelets play a crucial role in wound healing. Equine platelets are typically smaller, paler staining, and more uniform, compared to those of other domestic species.



Causes of Abnormally High Levels




• Physiologic (excitement causing splenic contraction)


• Primary thrombocytosis (rare myeloproliferative disorder, sometimes secondary to megakaryocytic leukemia)


• Secondary thrombocytosis (due to increased platelet production following cytokine release with inflammation, infection, anemia, leukopenia, and/or neoplasia or due to decreased removal by macrophages with excessive glucocorticoids)



Next Diagnostic Step to Consider if Levels High




• Examine blood smear to confirm the increase


• Repeat complete blood count (CBC) in several hours (physiologic thrombocytosis is transient)


• Look for signs of inflammation on CBC (ie, neutrophilia with left shift, increased fibrinogen, increased globulins), along with signs of anemia or leukopenia


• If no explanation is apparent, consider primary thrombocytosis and examine bone marrow



Causes of Abnormally Low Levels




• Decreased production


image Immune-mediated with antibodies against megakaryocytes

image Bone marrow hypoplasia secondary to certain drugs (estrogens), chemicals, mycotoxins, plant toxins (bracken fern), exposure to ionizing radiation
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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Platelets

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