Automated Techniques

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Automated Techniques

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

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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.

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• 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.

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• 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.

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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.

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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.

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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.

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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.

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• 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.

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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.

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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.

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• 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.

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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