- Impedance technology. This technology was originally known as the Coulter principle. There are several variations and adaptations to the impedance principle in use today from a variety of commercial manufacturers.
- Impedance technology is based on the fact that blood cells are poor conductors of electricity. Cells are diluted with an electrolyte, directed to a moving stream, and pass through a small orifice (opening) within a transducer (detection device). As each cell passes through the small opening of the aperture, an electrical field exists in the transducer; and when the cells pass through the aperture orifice (small opening), the increase in electrical impedance (resistance) is measured.
- Impedance technology provides a one-dimensional method for enumeration of the formed cellular elements as well as for cell sizing due to the resulting impedance signal being proportional to the cell’s (event) size.
- Different approaches to size discrimination (thresholding) and the cell dilution allow for accurate enumeration of RBCs, WBCs, and PLTs even though the absolute numbers (of cells) and size vary broadly within the blood. Displays of the cellular measurements are usually provided in a graphical form called a histogram (representing number of events versus relative size of the events).
histogram, frequency of events versus cell volume