Automated Testing Flashcards
Principle of electronic impedance in cell counting. What is it based on?
- cells suspended in conductive liquid (Isotonic diluent) that acts as electrical insulators
- flow of current is established between two submerged electrodes
- cells pass through an aperture by gentle vacuum/hydrodynamic focusing* = pulses and resistance to electrical flow can be counted and sized as a particle
*NOTE: Beckman vs Sysmex
Purpose of diluent in cell counting baths
“Number of voltage pulses” represents which hematologic parameter ?
Cell count
“Height of voltage pulses” represents which hematologic parameter ?
Cell volume
Define “co-incidence” in hematology
- 2 or more cells pass the aperture at the same time = 1 pulse counted as 1 cell
- cell count is falsely decreased and pulse height is falsely increased
How are histograms created ?
What is “aperture voting ?”
- Values counted in triplicate must match
- If 2/3 match = partial vote out
- If 2 or all 3 values do not match = total vote out
How is Hb value determined on Beckman Coulter ?
- lysing agent added to WBC dilution = lyses RBCs + release Hgb
- AFTER WBC COUNT, sample is taken to the SPECTROPHOTEMETER where Hgb is measured at 525nm
How is Flow Cytometry used to study cells ?
Forward light scatter: cell size
Side scatter: cell complexity/ granularity
VCS in Beckman Coulter analyzers
- differentiate WBCs
Volume:
Conductive:
Light Scatter:
Which WBCs are included in the 6-part differential on the Sysmex ?
- neutrophils
- lymphocytes
- monocytes
- eosinophils
- basophils
- myeloids
How do Sysmex analyzers differentiate WBCs ?
- fluorescent flow cytometry differentiates WBCs
- fluorescence = RNA/DNA content
- forward scatter = cell size
- side scatter = granularity/cell complexity
- polymethine dye is used to stain WBCs
- 6-part differential includes: neutrophils, lymphocytes, monocytes, eosinophils, basophils, and immature granulocytes /myeloids
Significance of increased retic count
Anemia due to red blood cells being destroyed earlier than normal (hemolytic anemia)
3 general causes of increased retic count
- Hemolytic anemia
- Blood loss
3.
How do Beckman Coulter determine retic count ? What parameters are used and how are they measured ?
- sample in stain chamber = NEW METHYLENE BLUE precipitates DNA in immature RBCs (increases granularity)
- VCS technology differentiates other cells from retics (decreased size and granularity)
How do Sysmex analyzers determine retic count ? What parameters are used and how are they measured ?
When would a manual retic count be indicated instead of an automated count ?
What stain is used for manual retic counts ? What does this stain do to retics ?
New methylene blue; causes clumping and staining of residual nucleic acid present in immature cells.
Minimum requirement for a stained red cell to be a retic
Manual staining procedure for retics (dilution, incubation time, etc.)
Manual counting procedure for retics (relative and absolute counts)
What are the allowable ranges (technical accuracy limits) when comparing retic counts on two slides ?
0 - 2%=
2.1 - 5%=
>5% =
Ref: relative retic count (>1 week old)
Ref: absolute retic count (>6 months old)