© Boule Medical AB, March 2018. Article no. 1504496 Page 73
8. Technology
Measuring Principles
SECTION 8. TECHNOLOGY
Measuring Principles
The measuring principles of the Exigo H400 analyzer are based on impedance and spectrophotometer
principles.
Whole Blood Dilution
The RBC and WBC concentration values are determined by counting cells in whole blood dilutions
of 1:40,000 for the RBC and 1:400 for the WBC and EOS.
Theoretical Principles (RBC Example)
If a sample contains 5 million red blood cells per µL, a dilution of 1:40 000 will give a nal
concentration of 5 million divided by 40,000 = 125 cells per µL. Each µL containing 125 cells, drawn
through the aperture, will generate 125 pulses.
Measured Volumes (Example)
The measured volume drawn through the aperture is 270 µL (manufacturer calibrated). Based on
the assumption made above, the system will count 270 × 125 = 33,750 pulses, which is equivalent to
5.0 × 10
6
cells/µL in the concentrated blood.
Theoretical Principles (WBC Example)
The measurement principle for white blood cells is the same as in RBC example but with a dierence
in dilution ratio and cell quantity. An example of this could be as follows: 5,000 cells/µL diluted
1:400 = 12.5 cells/µL.
Counting Time RBC and WBC
The counting time is dened as being the time needed for the sample to ll the metering unit from
the start to the stop detector.
Counting Time Limits
The normal counting time limits for the RBC and WBC/EOS metering units are between
18–30* seconds and 8–16 seconds respectively. If the counting time is below or exceeds the above
mentioned limits, the ag ST, TL or TU will be displayed.
The Counting Time is not related to the actual result. Atmospheric pressure variations, protein
built up within the orice (aperture) and other secondary eects that might cause pressure
changes will NOT aect the counted parameters RBC, PLT and WBC.
* refers to 60 μm orice instruments.
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