External quality assurance schemes in flow cytometry.

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.

Lymphocyte changes in secondary dengue fever: use of the Technicon H*1 to monitor progress of infection.

Secondary dengue fever as dengue hemorrhagic fever or dengue shock syndrome is a potentially fatal complication of an infection that presents with few clinical signs that help in the diagnosis. Previous workers have reported the value of buffy coat determinations of atypical lymphocytes as an aid to the diagnosis. We report here the use of an automated white blood cell differential counter, the Technicon H*1 in the monitoring of the atypical lymphocyte count as a measure of the progress of the infection in a retrospective study of serial full blood counts in 45 serologically confirmed patients. Technicon H*1 'basophil' and large unstained cell counts and manual atypical lymphocyte counts rose in tandem with the drop in platelets and decreased when the platelets recovered. In a sub-study, the atypical lymphocytes were immunophenotyped and found to be predominantly derived from T lymphocytes. We conclude that the Technicon H*1 is a useful monitor of the activity of the infection in dengue hemorrhagic fever.