1, electrical impedance, high frequency conductance and laser scattering combined detection method This is a new technology introduced by Coutler Company in 1987. Blood cells are suspended in electrolyte and pass through the inner and outer electrodes of the sensor with a certain current. Because of the high electrical impedance of blood cells, when blood cells pass through two electrodes, the impedance between the electrodes will increase instantly, forming an electrical pulse whose amplitude is proportional to the volume of blood cells. According to the pulse size, the cell volume can be measured. When measuring red blood cells, the pulse discriminator is used to remove platelet pulses with small amplitude, and the pulses of red blood cells and white blood cells are reserved. Because the number of white blood cells in blood is less than 1/500 of red blood cells, the total data is approximately considered as counting red blood cells. When measuring white blood cells, hemolysin is used to dissolve red blood cells, and then the remaining white blood cells are counted. When counting platelets, reduce the total threshold count of pulse discriminator and subtract the red blood cell count (including white blood cell count), which is the platelet count. Because different types of cells with the same volume produce the same pulse amplitude, it is impossible to distinguish them completely by volume alone. Using high frequency conductance method and laser scattering to analyze the internal structure of white blood cells can make up for this defect. Although the cell wall cannot pass through low-frequency current, it can pass through high-frequency current. The size and density of nucleus are different, and the impedance to high frequency current is also different, so it can be used to distinguish white blood cells. Laser scattering technology is mainly used to examine the surface characteristics and internal structure of cell membranes. Laser scattering has a strong ability to distinguish the structure and density of cell particles. The light scattering produced by coarse particles is stronger than that of fine particles, which can distinguish granulocytes. The STKS and MAXM series blood cell analyzers of COULTER Company in the United States adopt the combined detection methods of resistance method, high-frequency conductance and laser scattering. 2. The combined detection method of light scattering and cytochemical staining uses laser scattering and peroxidase staining techniques to classify cells. Eosinophils have strong catalase activity, neutrophil plasma is rich in catalase, followed by monocytes, with few protocells, while lymphocytes and basophils lack this enzyme. Trace blood is diluted with hypertonic liquid containing detergent and formaldehyde, and incubated for several tens of seconds. At this time, the cells are destroyed by the cleaning agent, and the enzymes in the leukocyte plasma are fixed. Then, the second reaction is continued, and hydrogen peroxide and tetrahydronaphthol are added for heating. At this time, the hydrogen peroxide in the cells to be tested is decomposed by catalase to produce oxygen, which makes tetrachloronaphthol develop color and precipitate and locate in the enzyme-containing particles. These cells are classified by light scattering of laser beams and different cell sizes. Obviously, basophils, lymphocytes and primordial cells cannot be detected because they do not contain this enzyme, so some instruments have specially set up basophil detection system, and its measurement channel adopts time difference method, which is the same as RBC/PLT measurement system. Due to the action of the reagent, all cells in the blood except basophils are dissolved. Basophils together with the naked nuclei of other cells produce a cell distribution map. The intact basophils are scattered at a high and narrow angle, located at the upper part of the figure, and the exposed particles are located at the lower part. Different naked particles have different distributions on the X axis due to different structures. The single nucleus is located on the left, and the more leaves, the more to the right. The ratio of angular scattering peak of lobulated nucleus to single nucleus is analyzed by computer, and the ratio is the result reported by the analyzer. TECHNICON H series analyzer adopts this technology. 3. Combined detection method of electrical impedance and radio frequency conductance This method uses four detection systems to detect different types of cells: ① Lymphocyte, monocyte and neutrophil detection system: hemolytic agent is added to cell suspension to dissolve red blood cells, so that white blood cells remain intact, and the morphology of cytoplasm and nucleus is similar to physiological state. When these cells pass through the detection system, white blood cells are jointly detected by electrical impedance method (measuring cell volume) and radio frequency conductance method (detecting cell nucleus and particle density). (2) Two detection systems for eosinophils and basophils: A special hemolytic agent is added to the cell suspension to dissolve or shrink all cells except eosinophils and basophils, and then the complete eosinophils or basophils are counted. (3) Detection system for immature cells: Sulfated amino acids are added to the cell suspension. Due to different occupations, immature cells bind more amino acids than mature cells and are resistant to hemolytic agents. When hemolytic agent is added, mature cells are dissolved, leaving only possible immature cells for counting. At present, NE 1500 of Japan East Asia Company and SE9000 of SYSNEX Company are classified by this method. 4. Multi-angle laser polarized light scattering detection method This instrument uses this technology to dilute the sample blood with a sheath. The internal structure of diluted white blood cells is similar to the natural state, and only basophils have a slight change in cell structure because of their moisture absorption characteristics. Hemoglobin in red blood cells is separated from cells under the action of high osmotic pressure. However, the water in the sheath flow enters the red blood cells, so that the cell membrane structure is still intact, which is the same as the refractive index of the sheath flow and does not affect the detection of white blood cells. At the same time, the instrument detects the scattered light generated by cells passing through the laser beam from four angles. 0 front-angle scattered light is used to measure cell volume,10 narrow-angle scattered light is used to measure cell structure, 90 vertical scattered light is used to measure intracellular particles and cytoplasm, and 90 depolarized light scattering separates eosinophils from other cells.