Quantitation of cell concentration using the flow cytometer.

A simple procedure has been developed to simultaneously measure cell concentration and analyze marker positive cell populations using the flow cytometer. Fluorescent latex particles of known concentration are added to the sample to be analyzed. Marker positive cells and fluorescent particles are then analyzed using flow cytometric methods. Since the particle concentration is known, the number of particles that have accumulated gives the exact volume of the sample analyzed. The concentration of total and marker positive cells that were analyzed then can be calculated. The method will be illustrated using single, dual, and triple laser excitation of cells stained for DNA content in combination with green or red fluorescent spheres. The usefulness of the procedure is demonstrated by counting cells from highly necrotic tumors where large amounts of debris are present.