🟡 Optical Fluorescent Platelet Count Optical platelet count is a parameter determined in the RET channel of automated hematology analyzers. This method is based on the use of semiconductor lasers in combination with fluorescent dyes (polymethines) that selectively stain RNA and DNA within cells.
During the analysis, cells are irradiated with a laser of a specific wavelength, which allows for the registration of three types of signals:
Forward Scatter (FSC) — reflects cell size. Side Scatter (SSC) — characterizes the size and number of intracellular structures. Side Fluorescence (SFL) — indicates nucleic acid content. Platelets contain a small amount of nucleic acids, which makes them more fluorescent compared to mature erythrocytes. At the same time, they are significantly smaller in volume than erythrocytes, which allows for easy differentiation on scattergrams. Theoretically, the optical method is capable of detecting platelets of all sizes.
Interpretation of the Scattergram The optical method allows distinguishing the following cell populations:
PLT-O (optical platelets) IPF (immature platelets) RBC-O (optical erythrocytes) RET (reticulated erythrocytes) LFR (low fluorescence reticulated erythrocytes) MFR (medium fluorescence reticulated erythrocytes) HFR (high fluorescence reticulated erythrocytes) Advantages of the Method The optical method effectively eliminates interferences arising from:
small erythrocytes, erythrocyte fragments, large platelets. Some modern hematology analyzers are also equipped with PLT disaggregation technology, which further increases the accuracy of platelet counting.
Source: Chen, Yong, Hu, Yonggang and Hu, Hai. “Advances and challenges in platelet counting: evolving from traditional microscopy to modern flow cytometry” Journal of Laboratory Medicine, vol. 49, no. 1, 2025, pp. 2-13.
