Cell counting

Cell counting is any of various methods for the counting or similar quantification of cells in the life sciences, including medical diagnosis and treatment. It is an important subset of cytometry, with applications in research and clinical practice. For example, the complete blood count can help a physician to determine why a patient feels unwell and what to do to help. Cell counts within liquid media (such as blood, plasma, lymph, or laboratory rinsate) are usually expressed as a number of cells per unit of volume, thus expressing a concentration (for example, 5,000 cells per milliliter). Cell counting is any of various methods for the counting or similar quantification of cells in the life sciences, including medical diagnosis and treatment. It is an important subset of cytometry, with applications in research and clinical practice. For example, the complete blood count can help a physician to determine why a patient feels unwell and what to do to help. Cell counts within liquid media (such as blood, plasma, lymph, or laboratory rinsate) are usually expressed as a number of cells per unit of volume, thus expressing a concentration (for example, 5,000 cells per milliliter). Numerous procedures in biology and medicine require the counting of cells. By the counting of cells in a known small volume, the concentration can be mediated. Examples of the need for cell counting include: There are several methods for cell counting. Some are primitive and do not require special equipment, thus can be done in any biological laboratory, whereas others rely on sophisticated electronic appliances. A counting chamber,(also known as hemocytometer), is a microscope slide that is especially designed to enable cell counting. The hemocytometer has two gridded chambers in its middle, which are covered with a special glass slide when counting. A drop of cell culture is placed in the space between the chamber and the glass cover, filling it by capillarity. Looking at the sample under the microscope, the researcher uses the grid to manually count the number of cells in a certain area of known size. The separating distance between the chamber and the cover is predefined, thus the volume of the counted culture can be calculated and with it the concentration of cells. Cell viability can also be determined if viability dyes are added to the fluid. Their advantage is being cheap and fast; this makes them the preferred counting method in fast biological experiments in which it needs to be merely determined whether a cell culture has grown as expected. Usually the culture examined needs to be diluted, otherwise the high density of cells would make counting impossible. The need for dilution is a disadvantage, as every dilution adds inaccuracy to the measurement. To quantify the number of cells in a culture, the cells can be simply plated on a petri dish with growth medium. If the cells are efficiently distributed on the plate, it can be generally assumed that each cell will give rise to a single colony or Colony Forming Unit (CFU). The colonies can then be counted, and based on the known volume of culture that was spread on the plate, the cell concentration can be calculated. This is often carried out following the stadard ASTM D5465