CLS 541-Advanced Medical Haematology M. sc. Program Lab-2- Automated Techniques CLS 541-Advanced Medical Haematology M. sc. Program Lab-2-

Introduction A variety of automated instruments for performing blood counts have been developed and are now widespread use. Semiautomated instruments often measure a small number of components e. g WBC and Hb. Fully automated multi-channel instruments usually measure 8-20 components, including some new variables which have no equivalent in manual techniques. High level of precision in automated instruments.

If use quality control and good calibrated the results will be very accurate. The most recently developed blood cell counters , have automated procedures for sample recognition e. g by bar-coding. In large laboratories (80-100 samples per hour) require fully automated blood counters capable of the rapid production of accurate and precise blood counts.

Choice of an instrument for an individual laboratory should take running coast, including maintenance and reagents; size of instrument requirement of service such water, compressed air, draining and an electricity supply with stable voltage. UK National health service medical devices agency.

Hb concentration Most automated counters measure Hb by a modification of the manual haemoglobincyanid method (HICN). Modification include alteration in the concentration of reagents and in the temperature and PH of the reaction. Measure the absorbance.

Red blood cell count Can be counted in system based on either: 1- aperture impedance 2- light scatter technology. A large numbers of cells can be counted rapidly, there is a high level of precision.

aperture impedance Impedance counting depends on the fact that red cells are poor conductors of electricity whereas certain diluents are good conductors; this difference forms the basic of the counting systems used in many instruments. Blood highly diluted in buffered electrolyte solution. The flow rate of this diluted sample is controlled. This result is measured volume of the sample passing through an aperture tube of specific dimensions.

Light scattering Red cells and other blood cells may be counted be means of electro-optical detectors. A diluted cell suspension flows through an aperture so that the cells pass, in single file, in front of a light source; light is scattered by cells passing through the light beam. Scattered light is detected by a photomultiplier or photodiode which converts into electrical impulses which a accumulated and counted.

The a mount of light scattered is proportional to the surface area and therefore the volume of the cell so that the height of the electrical pulses can be used to estimate the cell volume.

Haematocrite and red cell indices The term ‘haematocrite’(Hct) rather than PCV should be used for the automated measurement. The red cell indices included: MCV, MCH and MCHC; more recently; red cell distribution width (RDW). All these values will automatic calculation.

Total WBC count The total WBC is determined in whole blood in which red cells have been lytic. Can be counted in system based on either aperture impedance or light scatter technology. The precision of the automatic count was no better than that of manual count.

A three part differential count assigns cells to categories usually designed: (a) ‘granulocytes’ or ‘large cell’; (b) ‘lymphocyte’ or small cells; and ‘monocytes’ or ‘middle cells’. Both impedance counter or light scattering instrument are capable of producing three-part differential counts from single channel; the categorization is based on the different volume of various types of the cell following partial lysis and cytoplasmic shrinkage.

Platelet count and other platelet parameter Platelet can be counted in whole blood using the same techniques for counting red cells. Mean platelet volume (MPV) which vary inversely with platelet count in normal subject. Platelet distribution width (PDW) which is a measure of platelet anisocytosis and ‘plateletcrit’