Is the Miller disk of great value? Should I purchase it for manual reticulocyte counts?
A. A critical aspect of manual reticulocyte counts is assessing a sufficient number of red cells to ensure that the measurement is adequately precise. The minimum sample size for erythrocytes, within which reticulocytes must be enumerated, is 1,000, as defined by Poisson statistics (CAP hematology checklist item HEM.35300). Manually counting this number of cells obviously is labor intensive. The Miller disk is a counting aid that provides a standardized area in which to count erythrocytes. The disk incorporates a large square counting area within which is a square that is one-ninth the size. The number of erythrocytes in the large square is calculated by counting all erythrocytes, including reticulocytes, in the small square and multiplying by nine. This is followed by counting all reticulocytes in the large square. The latter number is then divided by the calculated number of erythrocytes in the large square and multiplied by 100 to derive the reticulocyte percentage. To ensure adequa
