Hematology analyzer is used to conduct a complete blood count (CBC), which include red blood cell (RBC), white blood cell (WBC), hemoglobin, and platelet counts, as well as hematocrit levels. This is why it is called a cell counter. There are two types of cell counters – 3-part differential cell counters and 5-part differential cell counters. All hematology analyzers use Coulter’s Principle. A 3-part differential cell counter uses Coulter's Principle to find the size and volume of the cell. Coulter's principle is applied through the use of two electrodes. Using hydrodynamic focusing, the sample cells are sent through an orifice one cell at a time. As the cells go through the orifice, they briefly cause electrical resistance to the current. This resistance is recorded, measured, amplified, and processed which can then be interpreted by the computer into a histogram. The 3-part analyzer is able to differentiate between 3 types of WBC's, neutrophils, lymphocytes, and monocytes. A 5-Part Differential Cell Counter utilizes both Coulter's Principle and flow cytometry to determine the granularity, diameter, and inner complexity of the cells. Just as in 3-part differential cell counter, the sample cells are passed through an orifice. Additionally, during this, a laser is directed at them, and the scattered light is measured at multiple angles. The absorbance is also recorded. The cell can be identified based on the intensity of the scattered light and the level of absorbance. A 5-part cell counter can differentiate all WBC types (neutrophils, lymphocytes, basophils, eosinophils, and monocytes). 5-part analyzers are more expensive than 3-part analyzers, but provide more in-depth information about the sample. Specific jobs, such as allergy testing, require 5-part differential analysis. However, most medical tasks can be completed with the 3-part analyzer. Popular brands of hematology analyzers are Sysmex, Horiba, Mindray, Erba, UBM etc.