Automation in Haematology

Question 1

State the principle of electrical impedance counting (incorporating Coulter’s principle).

Answer 1

Diluted EDTA blood, in a bath, is drawn through the aperture into an aperture tube by a vacuum. There is an electric current between the two baths. Each time a cell passes through the aperture, resistance occurs and a pulse is generated. This is registered as a count. The size of the cells is related to the amount of resistance generated and this can be used to calculate the MCV of all the cells that have been counted. RCC value is based on the number of pulses (>36fL). MCV is measured by averaging the amplitude of the pulses created, as the cells pass the aperture of the counter. Data is assembled into a cell-size histogram. Sensitivity can be adjusted to exclude platelets and WBC in a RCC. Sensitivity can also be adjusted for platelet counts and WCC

Question 2

What is the principle of light scattering?

Answer 2

Flow cytometry is a method to differentiate and count cells (and microparticles). Cells, in suspension, are passed by a focused light beam (laser), in a narrow stream. Optical (scatter/fluorescence) or electrical signals are sequentially generated by each single particle. Signals are detected and displayed for cell distribution analysis. Large numbers are analysed one after the other typically in about one minute. The detection limit is low i.e., it is a very sensitive technique. Flow cytometric/light scattering techniques are very useful for measuring white cells. Number of cells are counted. Cell size and complexity (granularity), staining characteristics can also be measured

Question 3

Peroxidase method involves the staining of neutrophils, _____________, and eosinophils with peroxidase, and the cells are counted based on size (forward light scatter) and staining characteristics.

Answer 3

Monocytes

Question 4

WBC DIFF/RET/PLT-F uses ______________ ____________ ________________, with markers for human progenitor cells (CD34+).

Answer 4

Fluorescence flow cytometry

Question 5

BC/PLT counts employ __________-focused impedance.

Answer 5

Hydrodynamically

Question 6

Automated ___________ count employs flow cytometry.

Answer 6

Reticulocyte

Question 7

Where a difficulty is encountered in performing a cell count or characterising a particular population of cell, a ‘_____’, or alarm, will be generated by the instrument.

Answer 7

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