Which machine uses a laser to detect different blood cell types?

• A. Coulter Counter
• B. Flow Cytometry
• C. Hematology Analyzer
• D. Microscope

Answer: (B)

Flow cytometry uses a laser as the light source and analyzes how cells scatter light and what fluorescence they emit. As cells pass in single file through the laser, forward scatter reflects cell size and side scatter reflects internal complexity; fluorescence from labeled antibodies or dyes reveals specific cell surface markers. By combining these signals, the machine can distinguish and quantify different blood cell types and subpopulations.

Coulter counters rely on electrical impedance to count and size cells, not on laser-based detection of cell types. A hematology analyzer is a general instrument for complete blood counts and may use various methods, but not the laser-driven, multi-parameter fluorescence approach. A microscope identifies cells by visual appearance, often with staining, not by laser-based detection of different cell types.