Quality control in image cytometry: DNA ploidy.

DNA ploidy has become a commonly performed quantitative image cytometry test in microscopic pathology. This has led to the need to develop quality control procedures to aid in assuring uniform and reliable test results. There are a number of unique issues related to the emerging technology of image analysis and its routine use as a quantitative microscopic assay that require consideration before establishing a quality control program. Previous considerations of this topic have primarily related to measurement issues, e.g., accuracy comparisons to other methodologies, calibration of instrumentation, sources of measurement error, and the interpretation of measurements results. Although these issues are critically important, with more routine usage the focus is now turning to quality control of the overall testing process in everyday use. Control charts and methods of controlling the total measurement process such as have been used in clinical chemistry, need to be established. As one of the first image assays in pathology, quality control procedures established now for DNA ploidy measurements could help shape the development of this field, especially as pathology transitions from being a subjective visual microscopic inspection process to a quantitative measurement process. This paper discusses these issues as they relate to overall quality assurance for the DNA ploidy test and describes a quality control program developed for an active breast cancer testing laboratory specializing in image cytometry tests, including DNA ploidy. The quality control program includes calibration control charts, control charts for internal diploid controls, check samples, and computerized individual histogram interpretation.