Module 3 Flashcards
What are properties of controls?
Number of analytes- single or multi
Concentration of analytes- different levels run
Matrix- should be same as patient sample
Liquid or lyophilized
What is a control range?
Acceptable range of QC values that accounts for normal day to day variations
If a value falls out of the range it indicates an error in the analytical system
How is a control range established?
Control sample is run repeatedly (min of 20 measurements over 10 days for initial range)
Mean and SD are calculated
Control limits are calculated- 1s, 2s, 3s (outliers are excluded if there’s less than 2)
What range is most often selected for control range limits and why?
2s
95% confidence interval
What is a quality control chart used for?
To quickly document, inspect and review control data
Graphical representation of observed control values to the expected results or control limits
What is the most common type of control chart?
Levey-Jennings
Each control level has its own chart
What must be done if a control value falls outside the control range?
Value must be clearly indicated
Value must be trouble shot, evidence of corrective action must be recorded
When the issue is resolved controls and patient samples are rerun
What types of error are there?
Random- unpredictable sources, positive or negative, any magnitude, increased scatter, decreased precision
Systematic- sources that produce consistent effects, one direction only, magnitude and direction may be predictable, can represent a shift or a trend, decreased accuracy
What are some cause of random error?
Bubbles or leaks
Poor mixing
Unstable temp or power supply
Poor technique
Dirty or damaged probes
What are some causes of systematic error?
Change in lot numbers
Deterioration of calibrators, controls or reagent
Deterioration of instrument components
Improperly prepared calibrators, controls or reagents
Overdue maintenance
Improperly performed maintenance
Overdue calibration
Environmental changes
What is multi rule QC?
A way to minimize the chances of false rejections while maintaining high levels of error detection
What is the principle of Westgard rules?
Control rules are associated with control values displaying certain patterns
Established parameters aid in detecting errors while minimizing false rejections and repeat runs
How can Westgard rules be described?
Within runs- only a single run of a control level or within one run of two levels ran at the same time
Across runs- occurs over more than one run
Within controls- violation by only one level of control
Across controls- violation including multiple control levels
What are the Westgard rules?
1-2s
1-3s
2-2s
R4s
4-1s
10x
7T
What are the characteristics of the 1-2s rule?
Random error
One result outside 2s
Further inspection
No rejection
What are the characteristics of the 1-3s rule?
One result outside of 3s
Random error (or large systematic)
Rejection
What are the characteristics of the 2-2s rule?
Two consecutive results outside 2s
Can be across runs or control levels
Systematic error
Rejection
What are the characteristics of the R4s rule?
4s spread between results across control levels
Random error
Rejection
What are the characteristics of the 4-1s rule?
Four consecutive results a outside 1s
Can apply across runs and levels
Systematic error
Rejection
What are the characteristics of the 10x rule?
10 consecutive results on one side of the mean
Across runs and levels
Systematic error
Rejection
What are the characteristics of the 7T rule?
7 consecutive results all trending in the same direction
Systematic error
Rejection
What happens when controls are run more frequently?
Errors are more likely to be detected
Greater chance of false rejection
What is the intent of multi rule QC?
Allow high level or error detection (probability of error detection, Ped)
Avoid too many false rejections (probability of false rejection, Pfr)
Pfr90%
What is a power function graph?
Plot of the relationship between error detection and false rejection
Assists in deciding the appropriate number of controls and rules
What is the difference between statistical and nonstatistical quality control?
Statistical- use of controls and QC charts to monitor performance of analytical methods and assess the validity of patient test results, detects error in procedures
Nonstatistical- procedures that maintain and improve performance, doesn’t actually monitor test result production, supports ability to ensure results are valid
