electrical impedance and colorimetric measurements
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7/27/2019 Electrical Impedance and Colorimetric Measurements
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Electrical Impedanceand
Colorimetric Measurements
Joanna Ellis, MLS(ASCP)
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Objectives
Cite the electrical impedance principle of cell
counting.
Identify and interpret microcytic and
macrocytic RBC histograms
Define coincidence
Identify the cell populations represented on a3-part differential WBC histogram
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HistoryYou CAN patent a hole
Prior to the 1950s blood cell counts were performed bymanual methods: Hemacytometer blood counts
Spun hematocrits
Spectrophotometrically determined hemoglobins Peripheral blood cell evaluation for all differentials
In 1953, Wallace Coulter patented the Coulter Principlein which particles are counted in fluid passed through ahole. The incredulous attorneys who had told himYou cant patent a hole were proven wrong.
Hematology automation has since grown to includeadditional principles such as optical light scatter andflow cytometry.
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The Coulter Principle
The poorly conductive blood cells are suspended in aconductive diluent (liquid).
The diluent is passed through an electric field createdbetween two electrodes.
The liquid passes through a small aperture (hole).
The passage of each particle through the aperturemomentarily increases the impedance (resistance) of
the electrical path between the electrodes. The increase in impedance creates a pulse that can be
measured.
The number of pulses = blood cell count
The amplitude (height) of the pulse = Volume of cell
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Electrical Impedance (The Coulter Principle)
Sweep Flow: Steady stream of diluent that flows behind each aperture to
prevent cells from re-entering the aperture
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Counting Chambers
Most common chambers using impedance:RBC/Platelet chamber
WBC chamber
RBC/Platelet Chamber
WBC Chamber
Differential ChamberReticulocyte Channel
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RBC/Platelet Chamber
Particle Size Cell the instrument Counts
2-20 femtoliters (fL) Platelet
36-360 fL Red Blood Cell
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RBC and Platelet Histograms
The black line represents normal cell distribution. The red line on
the RBC histogram graphically represents a microcytic red cell
population.
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Bimodal Histogram
Bimodal peak can be seen in situations such
Cold agglutinin disease
Post-transfusion
Post-treatment of IDA
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Coincidence
Coincidence: Multiple cells passed through theaperture at once.
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WBC Chamber
Lysing agent
In some analyzers the WBC count is directly measured byelectric impedance after the red cells have been destroyed by a
lysing agent. The lysing agent also shrinks the leukocyte cell
membrane and cytoplasm; therefore, the WBC count
represents the measure of the cell volume not native cell size.
Colorimetric measurements are used to determine hemoglobin.
Aperture in
electric field
WBCs
Hgb released
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Colorimetric Measurements
Hemoglobin is often determined by a colorimetric method.
Imidazole
Non-cyanide reagent with color change and read at 540nm
Instruments
Abbott CELL-DYN Sapphire Sodium Lauryl Sulfate
Non-cyanide reagent with color change and readspectrophotometrically
Instruments
Sysmex XT and XE Lysing agent converts free hemoglobin to cyanmethemoglobin
and read spectrophotometrically at 540nm.
Instruments
Advia 120
Some Beckman Coulters
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Three-part Differential
WBC Histogram
Lymphocytes: 35-92L
Mononuclear Cells: 92-152 fL
Granulocytes: 152-450 fL
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References
"Abaxis Veterinary Diagnostics - VetScan HM2 Technology."Abaxis MedicalDiagnostics - Redirect. Abaxis Medical Diagnostics, 2006. Web. 12 Sept. 2010..
Graham, Marshall Don. "The Coulter Principle: Foundation of an Industry." TheAssociation for Laboratory Automation :: Home. JALA Volume 8, Issue 6, Dec. 2003.Web. 12 Sept. 2010. .
Kelly, Kathleen. "Modules :: CLIA :: CME." Hematology in the Physician OfficeLaboratory Section I. University of Iowa Carver College of Medicine, 2008. Web. 12Sept. 2010..
Krantz, Alexander. "Residency & Fellowship Programs | Education." Department ofPathology & Cell Biology | CUMC. Columbia University of Physicians and Surgeons.Web. 12 Sept. 2010. .
Harmening., Denise, Clinical Hematology and Fundamentals of Hemostasis, 3rdedition, pp. 593-599.
Turgeon, Mary Louise, Clinical Hematology - Theories and Procedures, 3rd edition,pp373, 376-382.
Rodak, Bernadette, Diagnostic Hematology, 1st edition, p.605-606.
Coulter STKS Operating Manual
McKenzie, Shirlyn, Clinical Laboratory Hematology, 2
nd
edition,pp 813-829.
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