The flow cytometer (sy-TAH-mee-ter; cyto: cell, meter: measure) is a unique instrument used in both health care and research laboratories. Cytometry refers to the measurement of the physical and chemical characteristics of cells. Flow cytometry is the process in which measurements are made while cells in a liquid suspension are forced to flow one at a time through a measuring device.

Each of the types of immune system cells has a unique combination of size, shape, DNA content, and proteins. Using these measurements, scientists can use the flow cytometer to determine the amount of each type of cell in a blood or tissue sample.

Flow cytometers are also found in many hospitals for clinical uses. They are used to measure blood cell counts in patients infected with HIV and in patients with leukemia, cancer of the white blood cells. In the case of HIV-infected patients, the flow cytometer is used to count CD4+ T-cells, the cells that are killed by HIV. The response of leukemia patients to chemotherapy is monitored by counting the different types of leukocytes.

For example, a flow cytometer can be used to count the number and type of leukocytes (white blood cells) in a person’s blood. In a healthy person, granulocytes make up 50-60% of the total leukocytes and lymphocytes are about 30-40%. A person whose white blood cell counts differ from these numbers may be experiencing a problem with their immune system.

Doctors and scientists used to count cells with a microscope which is a very slow process. However, the invention of the flow cytometer allowed them to count thousands of cells in minutes and obtain much more detailed information.

But what exactly does the flow cytometer do?

Measures the physical and chemical characteristics of cells. It can measure a cell’s diameter, volume, surface area, and granularity.

Identifies and quantifies different types of cells by their surface proteins.

Determines a cell’s internal structure, including its DNA content, enzymes, and proteins.

In the Lab