A new assay for quantifying human reticulocytes.

The authors describe a new method for quantitative reticulocyte analysis. The assay uses a conventional clinical blood cell analyzer to size a patient's red blood cell neocyte population, which relates to the reticulocyte fraction in a linear fashion. Blood is layered atop Stractan (arabino-galactan polysaccharide) and centrifuged for 30 minutes at 1,500 X g. This density medium fractionation process enriches the Stractan layer with neocytes by up to 20-fold as determined by G6PD enzyme analysis. The mean corpuscular volume (MCV) of the red blood cells partitioning in the Stractan layer and the starting whole blood is then measured. The ratio of the two MCV measurements is then related to the reticulocyte percentage by a standard curve. In 93 patients, the derived MCV ratio was linearly correlated with manual reticulocyte counts (r = 0.96/slope = 0.99). Agreement of results obtained for single samples was within 0.2%. The assay's within-run and between-run precision is excellent (coefficient of variation less than 1%). The assay provides data on the percentage of reticulocytes in whole blood with an accuracy and precision that is at least 20 times greater than conventional microscopic technics.