Exam 3 Review Flashcards
Electronic impedance
Coulter principle of counting
Impedance = amt of resistance that a component offers to current flow in a circuit at a spec frequency.
Whole blood is passed between 2 electrodes thru an aperture so narrow that only 1 cell can pass thru at a time.
Change in impedance = proportional to cell volume (results in cell count and measure of volume)
Measurement based on electrical resistance prod by the cells as they pass thru the aperture
Which cells are pt of the 3-pt differentials?
Granulocytes, lymphocytes, monocytes
Factors affecting electronic impedance
Aperture diameter (how big is aperture/size of opening when blood is flowing down)
Protein buildup (have to remove the probe in this case)
Carryover from the prev sample (use a diluent to clean in between each specimen)
Coincidental passage of > 1 cell at a time
What are the common basic components of instruments?
Hydraulics (aspirator, dispenser, diluters, mixing chambers, flow cells [ex. Spectrophotometer]; mixed, incubated, and measured)
Pneumatics (vacuums, pressures for valves that move the specimen [filter changed every 2 weeks])
Electrical systems (operational sequence - electronic analyzers, computing circuitry)
Principle of measurement (Beckman Coulter instruments)
Aspirated blood is divided into 2 aliquots and mixed with isotonic diluent then passed thru either RBC or WBC aperture/channel.
Particles 2-20 fl are counted at PLTs, > 36 at RBCs
Looks at RBCs, WBCs, PLTs, Hb, Hct, MCV, MCH, MCHC, RDW, MPV, NRBCs, & WBC diff (3 pt and 5 pt)
May use diluents or pack-pack L which lyses RBCs, leaving WBCs
Ex. Hemocytometers which count RBCs, WBCs, and PLTs
Where do lymphocytes fall on a histogram
First, usually starts with a peak
50-90 fL
Where do basos fall on a histogram?
~100 fL
Right after lymphs
Kind of in the middle in the stagnant line with monos and eos
Where do monocytes fall on a histogram?
90-160 fL
Right after basos
Where do eosinophils fall on a histogram?
~ > 150 fL or between 150 and 200
After monos
Where do neuts fall on a histogram?
160-450 fL
After EOS
Identify abnormal histograms (also see pictures in notes)
Trends may be shifted or scaled more or less to the right/left or even the middle depending on where the peak is on the histogram.
A left shift in the WBC histogram with possible interference at the lower threshold region.
R2 flag indicates an interference + loss of valley owing to an overlap or insufficient separation between the lymph and mononuclear populations at the 90 fL region.
Determine what flags on a result sheet mean.
Suspect area in which any specimen or system flags will display. May indicate a value is high or low; any abnormality the instrument finds in the result/analysis. The value may be out of the reference range according to the instrumentation used.
May include morphology flags and specimen or system flags.
Beckman-Coulter instrumentation have user-defined flags set for distributional abnormalities like eosinophilia and pancytopenia.
Sysmex WBC flags
L = low
CL = critically low
H = high
CH = critically high
—– = Interference
***** = unsure/unknown
Limitations of instrument performance
Instrument limitations; common method limitation
Specimen limitations (common, what you report based on your lab)
- Cold agglutinins (cold Ab making blood react to temps)
- Icterus (high proteins in the plasma that makes it very yellow/deep yellow)
- Lipemia (byproducts can’t pass thru b/c too thick/opaque)
- Age and improper handling (conformational change to cold temp; refrig spec/frozen should not be used unless it’s for blood banking)
Why is it important to perform cell counts ASAP?
WBCs deteriorate within 30 minutes.
