Which device uses electricity to count different blood cell types?

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

Answer: (C)

The key idea is counting cells using electrical impedance. A Coulter counter works by suspending blood in a conductive liquid and pushing it through a tiny aperture between two electrodes. As each cell passes through, it briefly changes the electrical resistance, producing a pulse. Each pulse corresponds to one cell, so counting pulses gives cell counts, and the height of each pulse relates to the cell’s size, which helps distinguish larger white blood cells from smaller red blood cells and platelets. Because it relies on electrical changes rather than light or fluorescence, it fits the description of using electricity to count different blood cell types. Flow cytometry, hematology analyzers, and spectrophotometers use other principles—laser/fluorescence for identification, or light absorption—which aren’t purely electrical counting like the Coulter method.