Fundamentals of Clinical Testing - Principles of Hematology Analyzers
Principle of electrical detection
1. Electrical Impedance Method—Classic Coulter’s Principle
When the isotonic buffer is injected and the low-frequency direct current is applied, the inner and outer electrodes and the buffer form a current loop. When the cell suspension is sucked through the gem counting hole on the small hole tube by negative pressure, due to the relatively non-conductive characteristics of blood cells, the resistance in the induction area of the small hole in the circuit suddenly increases, causing instantaneous voltage changes to form pulses Signal.
The strength of the pulse signal reflects the size of the cell volume, and the amount of the pulse signal reflects the number of cells.
These pulse signals go through amplification, threshold adjustment, screening, shaping, counting and automatic control protection system to complete the counting and volume determination of blood cells.
Three-class blood analyzers mostly use the principle of electrical impedance.
2. Radio frequency conductometric method
High-frequency current can pass through the cell membrane. Due to the different internal structures of different cells, the electrical conductivity is also different. Therefore, high-frequency electromagnetic probes are used to detect the electrical conductivity of cells. Cell classification is performed using characteristic information such as composition (size, density).
Principle of Optical Detection
1. Light Scattering by Laser Scattering
The cell suspension after being diluted, dyed, etc. is injected into the center of the sheath fluid, and the cells are arranged neatly and singly along the two streams of the suspension and the sheath fluid, and pass through the detection area at a constant flow rate.
When the cells are irradiated by the laser beam in the detection area, they can block or change the direction of the laser beam due to their own characteristics (such as volume, degree of staining, size and number of cell contents, density of the nucleus, etc.), resulting in various angles corresponding to their characteristics. The scattered light signal can be received by signal monitors at different angles:
(1) Low-angle scattered light, also known as forward-angle scattered light, reflects the number and surface volume of cells (or particles)
(2) High-angle scattered light, also known as side-angle scattered light, reflects the complexity of particles and nuclei inside cells
Scattered light techniques can detect stained cells, including fluorescent and non-fluorescent dyes. Different types of cells are stained with dyes to different degrees, and the resulting scattered fluorescence and scattered light changes are also different, so normal types of cells (or particles) can be accurately distinguished.
2. Spectrophotometry
Mainly used for hemoglobin determination.
Follow the Lambert-Beer law.
