Introduction

Flow cytometry, during the 1990s has become an integral part of diagnostic pathology. Indeed, many pathology laboratories currently use flow cytometry routinely to provide diagnostic and therapeutic support for clinicians treating a wide variety of malignant and nonmalignant disorders. Leukaemia immunophenotyping and the monitoring of lymphocyte subset counts are two of the most common uses, while flow cytometry is being increasingly used to determine the optimum time for peripheral blood stem cell (PBSC) harvesting, as well as for leukocyte and reticulocyte counting, platelet analysis (e.g. Bernard–Soulier and Glanzmann's syndrome) and red cell analysis (e.g. paroxysmal nocturnal hemoglobinuria and feto–maternal hemorrhage). In the twenty-first century, the flow cytometer is poised to revolutionise DNA and RNA molecular analysis through technologies such as multiplexing. The need to have instrument and methodological quality control procedures in place has become paramount as the use of the flow cytometer increases in the clinical setting. These proceduresmust be used in such a manner that they underpin the quality of results generated and should be performed frequently enough to identify problem areas. Consequently, it is essential to have both internal quality control (IQC) and external quality assessment (EQA) procedures in place. This chapter will focus on the current issues of IQC and EQA and highlight problems that may manifest during flow cytometric procedures.

Internal quality control

IQC can be defined as a set of procedures that monitor the instrument, analytical method and operator performance, as well as validating the reports generated. Such procedures are generally performed on a frequent enough basis to ensure that drift, or bias, can be detected and they should be supported by fully documented standard operating procedures.