External quality assurance schemes in flow cytometry.

ABSTRACT

Quality assurance schemes were devised to monitor the performance of laboratory tests commonly utilized in routine clinical practice. In the area of Flow Cytometry, external quality assurance schemes are very much in their infancy. There are 3 major applications of Flow Cytometry in the clinical laboratory lymphocyte subset enumeration, CD34 enumeration and leukemia immuno-phenotyping. Pilot schemes for CD34 enumeration and leukemia immuno-phenotyping have revealed a considerable lack of consensus with a wide divergence in practices. The coefficient of variation in reported results from these assessments have been very large, ranging from 20-200%. Results for lymphocyte subset enumeration surveys are sometimes not much better despite having been around for a longer period of time. Quality assurance programs in Flow Cytometry are difficult to conduct and 3 or 4 concurrent factors are often cited as reasons for the large variability. The need for viable, functionally intact cells as suitable assay material is probably the biggest contributor to the large variability. This difficulty in providing stable cells for inter-laboratory comparison is compounded by the lack of consensus in testing methodology. Participation in a distant external quality assurance scheme is consequently not very helpful to improving the practices in the laboratory. Currently, there are more problems than solutions. An awareness of these issues will hopefully contribute to the development of future consensus and offer up solutions to some of these problems.