13] Determination of platelet volume and number

Abstract

This chapter discusses the methods of determining platelet volume and number. The most suitable methods of platelet counting are direct methods with electronic particle counters. Phase microscopy is preferable only when electronic counting is impractical. In platelet counting with a phase microscope, whole blood is diluted with ammonium oxalate solution. Half of the mixture is put into each side of a hemacytometer chamber and all 25 squares are counted in duplicate under phase microscopy. Platelets are the only blood cells remaining intact to be counted. Electronic particle analyzers distinguish particles on the basis of impedance or optical density. They allow the quantitation of several cell types, including platelets, from a small blood sample and offer the statistic soundness of a 10,000-cell count. This is the method of choice when such an instrument is available and the platelets are from species with suitable platelet sizes, including platelet count, mean platelet volume, and a platelet volume histogram. Some instruments also offer an assay of the heterogeneity of a platelet size.