Mean Platelet Volume

Platelet size can be measured directly by automated hematology analyzers, expressed as mean platelet volume (MPV). Platelet size is determined at the time of platelet production from megakaryocytes. There is evidence that MPV is increased when both platelet production and destruction are increased, probably mediated by cytokines such as interleukin-3, interleukin-6, and thrombopoietin. There is also evidence that larger platelets are functionally more reactive, produce more thromboxane A2, aggregate more readily in vitro, contain more dense granules, and show increased expression of membrane receptors.

Elevated MPV has been associated clinically with cardiovascular and cerebrovascular morbidity. Elevated MPV has been identified as an independent risk factor for myocardial infarction in patients with coronary heart disease (Brit J Haematol, 2002, 1178,399-404), and for death or recurrent ischemic events after myocardial infarction (Lancet, 1991, 338:1409-1411). MPV has also been shown to be a strong independent predictor of impaired angiographic reperfusion and six month mortality in acute myocardial infarction treated with percutaneous coronary intervention (J Am Coll Cardiol, 2005, 46:284-290). An increase in MPV is independently associated with acute stroke (Stroke, 1995, 26:995-999), and an elevated MPV has been associated with a worse outcome in acute ischemic cerebrovascular events (Stroke, 2004, 35:1688-1691).

It is difficult to ascribe risk to a specific MPV value, however extrapolating from the above studies, an MPV of approximately 12.0fL or greater may be considered a risk factor for these vascular complications. Increased MPV values have also been reported in patients with vascular risk factors such as diabetes mellitus (especially when associated with microvascular complications), hypercholesterolemia, and smoking.

In a recent study (Brit J Haematol, 2005, 128:698-702) MPV was shown to be one of the laboratory values that may assist in elucidating the cause of thrombocytopenia. This parameter was significantly higher in patients with immune thrombocytopenic purpura (peripheral platelet destruction), than in aplastic anemia (decreased platelet production). An MPV greater than 12fL was only 59% sensitive, but was 95% specific for a diagnosis of immune thrombocytopenic purpura.

In summary, together with other clinical and laboratory parameters, the MPV may contribute useful information in individual patients regarding cardiovascular and cerebrovascular risk, and may also help in the evaluation of unexplained thrombocytopenia. Starting in mid-May 2008, Saint Luke's Regional Laboratories will begin reporting MPV together with all routine CBC's (one 5ml purple-top tube required.) The reference range is 9.4-12.3fL.




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