Here are the main applications of the hemocytometer:
- To perform blood counts: blood is a fluid that naturally carries cells throughout the human (or animal) body. In turn, blood is a mix of different types of cells that carry oxygen or fight infection, among others. They are distinguishable to the experienced eye by their shape and size. So, by counting separately all the cell types visible in the hemocytometer and calculating their concentration, we can not only get the cell numbers in the whole body, but also the percentage of each of them. This is very valuable for doctors to know if you’re within the levels established for a healthy person.
- To perform sperm counts: the concentration of sperm in semen is important in order to assess the male’s fertility. For humans, values above 15 million per milliliter are normal. Because sperm cells are moving cells, they need to be immobilized prior to counting. There are also special hemocytometers that are used for sperm, due to the cells’ smaller size: Makler or MTG hemocytometers.
- To process cells for culture: when culturing cells in the lab, the medium that contains the nutrients needs to be renewed once in a while. Cells can be counted as long as they have been put in solution. This includes adherent cells for cell culture, or suspension cells if they originally come from blood, but also bacteria and yeast. A popular example is in the preparation of yeast for the fermentation of beer.
- To process cells for downstream analysis: accurate cell numbers are needed in many tests for the quantification of proteins or DNA, while some others require high viabilities for them to be valid.
- To determine the size of a cell: because the size of the hemocytometer’s squares is known, you can take a picture of your cell suspension in the hemocytometer with your microscope. Then, with a program like ImageJ, set the scale to the size of a square side (1mm for the larger squares, for example) and by drawing a line on top of a cell it will tell you what the real size is. You can even count several to have an average size.
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I did my PhD in the Department of Chemical Engineering at Imperial College London. My research focused on mathematical modeling of the cell cycle in leukemia and involved experiments with cell lines. During that time, I had to count cells with a hemocytometer so often to track growth that I got tired and decided to build an app, HemocyTap, and share my knowledge on the topic here to help as many people as possible.