Quality Control Flashcards
closeness to true value
Accuracy
ability to yield same numbers, indicated by SD
Precision
Controls (QC)
- used to monitor accuracy and precision of patient results
- typically a commercial (synthetic) material analyzed along side patients to assess analyzer function
- controls MUST be within range in order to report patient results
values assigned by manufacturer (ranges stated in package insert)
Assayed Controls
values determined by each lab (ranges recommended by company)
Unassayed Controls
Calibration Stability
- time period specifying the validity of an analyzer’s accuracy and/or precision
- “Standards” of known concentration are used to calibrate analyzers
- labs determine the lowest and highest values accurately measured on analyzer
- performed periodically and posted near analyzer
Linearity Range
Reference Range (Normal Range)
- calculated by each lab for each test
- typically a minimum of 25 “healthy” patients are analyzed and statistical calculations are performed, such as mean and SD to determine ranges
Pre-Analytical Variation
occurs before the specimen is analyzed
Analytical Variation
occurs during the diagnostic testing process
Post-analytical Variation
occurs after the test is preformed
checks tor analytical errors, compares current results with previous results
Delta Checks
maintenance performed at specified intervals by staff or field engineers
Preventative Maintenance
how quickly a lab can complete the analysis of a test -request to result
Turn Around Time
unknown specimens sent to labs and compared against referred values
External QC Program
Proficiency Survey
consists of specifically prepared unknown specimens (proficiency samples), shipped to labs by independent manufacturer, labs analyze unknown samples and submit results
Standard Deviation Index (SDI)
- measure of the difference between several lab QC submissions
SDI = (value - group mean)/group standard deviation
What % of QC points falls within ± 1 SD?
68 %
What % of QC points falls within ± 2 SD?
95 %
What % of QC points falls within ± 3 SD?
99.7 %
2SD
SD x 2
3SD
SD x 3
%CV
(SD/Mean) x 100
Interpretation of QC data involves both ____ and ___ methods.
Graphical
Statistical
Dates of analyses are plotted along the ___-axis.
X
QC points are plotted on the ___-axis.
Y
The mean, ± 1 SD, ± 2 SD, and ± 3 SD limits are marked on the ___-axis.
Y
QC interpretation detects what 2 things?
- Increased random error
2. Shifts or trends in calibration
Random Error
- Affects the reproducibility or PRECISION of a test system.
- Can occur with:
# variations in voltage
# pipette techniques
# dispensers
# contamination
# volume dispensed
# bubbles in lines of reagents, etc. - Detected with 1(3s) or R(4s) Westgard Rules
Systematic Error
- Affects the ACCURACY of the test system in terms of bias, shifts and trends.
- Can occur with:
# calibration changes
# temperature changes
# light source deterioration
# electronics
# reagent lot changes, etc. - Detected with 2(2s), 4(1s), or 10(x) Westgard Rules
Westgard Rule 1(2s)
- When one control value exceeds ± 2 SD.
- *Warning Rule
Westgard Rule 1(3S)
- When one QC point exceeds ± 3 SD.
- Patient results and QC values should be rejected and rerun.
- *Random Error
Westgard Rule 2(2S)
- When 2 consecutive QC points exceed + 2 SD or -2 SD on the same side of mean.
- Patient results and QC values should be rejected and rerun.
- *Systemic Error
Westgard Rule 4(1S)
- When 4 consecutive QC points fall on the same side of the mean.
- Patient results and QC values should be rejected and rerun.
- *Systemic Error
Westgard Rule: R(4S)
- When one QC point exceeds the mean + 2 SD and another exceeds the mean – 2 SD (opposite sides of the mean).
- Patient results and QC values should be rejected and rerun.
- *Random Error
Westgard Rule R(10x) or 10X
- When 10 consecutive QC points fall on one side of the mean.
- Patient results and QC values should be rejected and rerun.
- *Systemic Error
8x
reject when 8 consecutive control measurements fall on one side of the mean
12x
reject when 12 consecutive control measurements fall on one side of the mean
