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Automated CBC Parameters
and
Quality Control
Joanna Ellis, MLS(ASCP)
The Automated
Complete Blood Count
The CBC is a very common test. Many patients will have baseline CBC tests to help determine their general health status. If they are healthy and they have cell populations that are within normal limits, then they may not require another CBC until their health status changes or until their doctor feels that it is necessary.
If a patient is having symptoms such as fatigue or weakness or has an infection, inflammation, bruising, or bleeding, then the doctor may order a CBC to help diagnose the cause.
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CBC Parameters
PARAMETERUNIT OF REPORTINGCOMMON METHOD OF DETERMINATIONWBCX 103 /LImpedance count X calibration (cal) factorRBCX 106 /LImpedance count X calibration factorHGBg/dLColorimetric absorbance in proportion to hemoglobinMCVfLFrom RBC histogram, #of RBCs X size of RBCs X cal constant OR Calculated: HCT X 10 RBCHCT%Calculated: RBC X MCV 10MCHPgCalculated: HGB X 10 RBCMCHCg/dL or %Calculated: HGB X 100 HCTRDW%Impedance (from histogram)PlateletX 103 /LImpedance count X cal factorWBC DiffAbsolute: X103 /LPercent of WBC : %Light Scatter , flow cytometryWe have discussed the principles of impedance, colorimetric determinations, light scatter, and flow cytometry in the previous powerpoints. This chart simplifies the parameter, the units of reporting, and the most commonly used method of determination.
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M77221
CBC
Adult Reference Ranges
This chart can also be found in on the first page of the textbook.
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Linearity
(Reportable Range)
The instrument will be accurate as long as the results fall within a certain range known as the linearity range also known as the reportable range. When patient results are higher or lower than the reportable range, the results do not match up the standard curve or calibration curve in a straight line; therefore, they cannot be standardized. The results cannot be reported. Some instruments FLAG these results, others give values of greater than the highest reportable value. Many times the specimen will need to be diluted, rerun and the result multiplied by the dilution factor to get a result within linearity.
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Advia
Linearity Instrument Codes
These codes are on the CBC results sheet when a certain parameter is beyond set limits. There are abnormal results that generate flags or abnormal codes. We will be discuss the document Handling Abnormal Results next.
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CBC Quality Control
Commercial Controls:
3 levels (low, normal, high)Values stored in instrument computerLevey-Jennings graph generated and stored for each parameterMode to Mode QC:
Most automated hematology instruments have a primary and secondary mode of sample aspiration. Controls must be run on BOTH and correlate.Primary=Automated or ClosedSecondary=Manual or OpenDelta Checks
When the Laboratory Information System (LIS) and the instrument are interfaced (connected) delta checks are conducted by the LIS on select parameters.Current values compared to most previous resultDifferences greater than the limits set within the LIS are flagged*
WBC Parameter
Interfering substances and Implications
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RBC Parameter
Interfering substances and Implications
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HGB Parameter
Interfering substances and Implications
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HCT Parameter
Interfering substances and Implications
MCV Parameter
Interfering substances and Implications
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RDW Parameter
Interfering substances and Implications
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Plt Parameter
Interfering substances and Implications
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WBC Differential Parameters
Clinical Implications in Adults
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References
Harmening., Denise, Clinical Hematology and Fundamentals of Hemostasis, 3rd edition, 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, 2nd edition,pp 813-829."Complete Blood Count: The Test." Lab Tests Online: Welcome! American Association for Clinical Chemistry, 18 June 2010. Web. 13 Sept. 2010. ."WBC Differential Count: The Test." Lab Tests Online: Welcome! American Association for Clinical Chemistry, 18 June 2010. Web. 13 Sept. 2010.http://www.labtestsonline.org/understanding/analytes/differential/test.html#what>.*