The Number of Pulses Seen on Impedance Counters is Proportional to Cell Concentration
The number of pulses seen on impedance counters is directly proportional to the number or concentration of cells in automated cell-counting instrumentation. 1
How Impedance Cell Counting Works
Impedance-based cell counting (also known as the Coulter principle) works through the following mechanism:
- When cells pass through a small measurement channel or aperture, they displace electrolyte solution
- This displacement causes a measurable change in electrical impedance
- Each cell passing through the aperture generates one pulse
- The number of pulses directly corresponds to the number of cells in the sample 1, 2
Technical Details of Impedance Cell Counting
Impedance cell counters operate based on these key principles:
- The counter detects changes in electrical resistance when a cell passes through a small aperture
- Each cell generates a distinct electrical pulse as it passes through the detection zone
- The pulse count provides a direct measure of cell concentration in the sample
- The magnitude of each pulse is proportional to cell volume, not just cell number 3
Characteristics of Cell Counting by Impedance
The cell counting process using impedance technology has several important characteristics:
- It follows a non-homogeneous Poisson process over time 1
- The electrical cell counts typically show a log-normal distribution
- The time difference between cell occurrences follows an exponential distribution 1
- For accurate counting, appropriate sample dilution may be required for high cell concentration samples 1
Advantages of Impedance Cell Counting
- Provides rapid results with small sample volumes
- Enables label-free detection without requiring cell staining
- Allows for real-time monitoring of cell populations
- Can detect as few as 20 cells/μL in some microfluidic systems 2
- Provides both quantitative (cell number) and qualitative (cell size) information 3
Common Applications in Clinical and Research Settings
Impedance cell counting is widely used in:
- Complete blood count analysis
- Cell viability assessment
- Cell proliferation studies
- Monitoring cell invasion processes 4, 5
- Disease diagnostics in humans and animals 1
Pitfalls and Considerations
When using impedance counters, be aware of:
- Cell diffusion characteristics vary based on cell size (smaller cells like lymphocytes diffuse more than larger cells like granulocytes) 1
- High cell concentrations may require sample dilution to prevent coincidence (multiple cells passing through the aperture simultaneously) 1
- Parasitics (alternate signal routes) can affect impedance measurements at higher frequencies 3
- The resistive contribution from conductors can influence impedance readings 3
In summary, impedance counters generate pulses that directly correspond to the number of cells passing through the detection aperture, making the pulse count proportional to cell concentration in the sample.