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Basic Platelet Biology
There are a variety of platelet disorders that can stem from congenital platelet defects (e.g., von Willebrand disease, hemophilia A) or from external factors (e.g., acquired from taking certain medications). In 2020, over 210,000 people worldwide were living with hemophilia disease and 84,000 were living with von Willebrand disease.1 As an X-linked recessive condition, hemophilia affects males more than females,2 while von Willebrand disease3 and many other bleeding disorders4 affect females more frequently than males.
Platelets, or thrombocytes, are small fragments of megakaryocyte cells and are vital for normal blood clotting. As with other blood cells, platelets are produced in the bone marrow. Generally, a healthy person’s blood is about 60% plasma and about 40% red and white blood cells.5 Although there are about 150,000-350,000 platelets per microliter of blood, platelets are so small that they don’t warrant a volume percentage.5 When a blood vessel is injured, hemostasis is initiated. Platelets are attracted to the wound, become sticky, and adhere to the injury site causing more clotting factors to be released. More platelets bind to the site, fibrin and thrombin are activated, red blood cells are trapped in the fibers, and ultimately, a clot is formed.
High platelet levels can lead to excessive clot formation. There are two main high-platelet conditions. Thrombocythemia, also called Essential Thrombocythemia, is a rare myeloproliferative neoplasm where the bone marrow produces too many megakaryocytes leading to too many platelets. Thrombocytosis, or secondary thrombocytosis, is a high platelet count caused by another condition such as infection or inflammation.6 In both conditions, abnormal blood clotting, thrombosis, can lead to strokes, embolisms, and thromboses. Conversely, low levels of platelets, thrombocytopenia, occurs either when there are too few platelets produced, when too many platelets are destroyed, or when the platelets don’t function correctly. Because platelets are required for clot formation, thrombocytopenia can result in abnormal bleeding (e.g., excessive nose bleeds), petechiae (tiny bruises under the skin), and prolonged bleeding.
Platelet function assays and platelet levels, which can be done independently or as part of the CBC with differential, are done to evaluate platelet quantity and show how well those platelets work. Mean platelet volume is a measurement of platelet size and provides further information on platelet function. Together, these results may provide diagnostic predictive value and aid in clinical decision making.
What is Mean Platelet Volume?
In addition to knowing the number of platelets, it is important to understand platelet size. The Mean Platelet Volume (MPV) parameter, the average volume of individual platelets, is derived from the PLT histogram (Figure 1). A high MPV, indicating larger platelets, is indicative of more young platelets in the blood. Following blood loss or destruction of platelets, the bone marrow releases more megakaryocytes, which in turn, are fragmented into large platelets. Coupling the platelet count with the MPV can indicate different associated conditions.
Figure 1. Normal PLT histogram.
Like a high MPV indicates younger platelets, a low MPV indicates older platelets and can be indicative of disease. For example, low MPV has been associated with diseases including systemic lupus erythematosus,7 hypothyroidism,8 and HIV infection.9 Low MPV may also simply be a response to medications such as heparin.
Neither the platelet count nor the MPV test is diagnostic, but both can aid in clinical decision making and suggest the need for and direction of further testing.
Advancing Hematology to Improve Diagnosis
The patented advancements of the Enhanced Coulter Principle allow a high-quality, reportable MPV, for every patient sample—even for thrombocytopenic patients. Using counter and pulse analyzer circuits, the number and volume of particles passing through the sensing zone can be measured. The volume may be represented as the equivalent spherical diameter, and measured particle sizes can be binned using a height analyzer circuit and a particle size distribution. The MPV parameter is measured in triplicate from the three apertures on the analyzer and voting is performed comparing data for all three apertures. Results are produced by averaging the parameters obtained from the apertures that are within the established statistical range. During the sensing period, a steady stream of diluent, called the sweep flow, flows behind the RBC aperture. The application of sweep flow prevents the recirculation of cells behind the aperture and prevents cells from re-entering the sensing zone and being counted as platelets.
PLT count and MPV measurements are included as a standard part of the CBC with Differential. And because the Enhanced Coulter Principle is used for every patient sample without the need for reruns, you improve throughput and save on premium-priced reagents.
Discover how our advanced IVD hematology parameters can aid in patient management.
