Advances in Platelet Counting

Accurate and reliable platelet counting is critical for the clinical management of platelet disorders, especially in thrombocytopenia. The platelet count is used to determine if the patient requires a platelet transfusion. As the prophylactic transfusion trigger is now set anywhere between 10-20 × 10(9)/L (depending upon the institution) it is therefore important that reliable and accurate counts are obtained in severely thrombocytopenic samples. The accuracy and precision of automated platelet counts is totally reliant upon optimal discrimination of platelets from other cells and interfering particles. However, clinicians often still rely upon counts that have been generated using so called "1-dimensional" cell size analysis systems, which not only fail to discriminate platelets from cell fragments of similar size but exclude large platelets from the final count. Also the current reference method for platelet counting (the manual phase count), upon which analysers are usually calibrated is highly imprecise, time consuming and unreliable. Thus there has been a demand for improvements in platelet counting technology in order to improve accuracy of counting in thrombocytopenia so that correct clinical decisions can be made. More recent developments including the introduction of "2-dimensional" optical counting and immunoplatelet counting within automated systems are significant advances. The availability of new technologies coupled with the recent development of a new candidate international reference method (flow cytometric immunocounting using the PLT/RBC ratio) should therefore improve the overall reliability of platelet counting especially in thrombocytopenia. In this review, the history and recent advances in platelet counting methodologies will be presented. The relative advantages and disadvantages of each technology will then be discussed along with their potential impact on improved accuracy of platelet counting.