Principles of flow cytometry

Clinical flow cytometry is a relatively new and rapidly growing medical technology. According to estimates, there were less than 1000 instruments in operation globally prior to 1985. Most of these instruments were used exclusively for research, and required dedicated facilities and operators with extensive backgrounds in electronics. In the mid-1980s, with the availability of benchtop clinical models, the number of flow cytometers jumped dramatically, surpassing 4000 by 1990. Most of the instruments that have been sold in the past decade are equipped with low power, air-cooled argon ion lasers with a fixed emission light wavelength at 488 nm. They are capable of multi-color immunophenotyping, and are usually connected to powerful personal computers for data analysis. By 1992, there were an estimated 7000 flow cytometers in operation worldwide. Today, the three general fields where this technology is well established are clinical immunology, laboratory hematology, and medical oncology. The most prominent uses of flow cytometers are for immunological characterization of lymphomas and leukemias, crossmatching tissues for organ transplants, and counting lymphocyte subpopulations in the peripheral blood of HIV-infected individuals. In this review, a brief historical introduction will be followed by a general description of some of the salient features of clinical flow cytometers.