Module 3 Flashcards
Statistical QC
use of controls and qc charts to monitor analytical methods Known concentrations of analytes
Non statistical QC
procedure which maintains and improves performance
examples of non statistical QC
produce and monitor high quality water Calibrate lab equipment as schedules monitor temps document maintmance
purpose of running controls with patient tests
to detect error int he procedure
Properties of controls
Number of analytes: single or multi Concentration of analytes: Different levels Matrix: same physical and chemical matrix as patient samples May be liquid or lyophilized
Control range
acceptable range for normal day to day variation
how to establish a control range
control sample ran minimum 20 times over 10 days to establish initial range Mean and SD are calculated Distribution is assumed Gaussian; any values outside of +-3SD are excluded and mean and SD are recalculated using remaining data
+/- 1S contains about
68% of the values
+/- 2S contains about
95% of the values
+/- 3S contains about
99% of the values
95% confidence interval
+/- 2S range is selected for control range. This means 95% of all control values should fall in this range
Levey Jennings Chart
Statistical QC Results on y axis, time on x axis Range should be big enough for +/- 4s
Levey jennings chart must be labeled with (7)
Name of test Name, level, lot # of control material Units of measurement Analytical system Mean and SD Time period covered by chart
What to do if control value is out of range
plot on chart Circle with red ink Troubleshoot and document Control must be in range in order to release patient results
Types of errors
Random: increased scatter, decreased precision Systematic (Shift): error sources that produce consistent effects on values; pos OR neg Systematic (Trend): ex. reagent breaking down
*************** Error type: Random Examples of causes
Bubbles or leaks Poor mixing; precipitates in reagents/controls Unstable temp or power supply Poor technique Dirty or damaged probes
*************** Error type: Systematic Examples of causes
MOST COMMON: Change in lot # (calibrators, controls, reagents) Improperly prepared solutions Deterioration due to improper storage/handling Less common: Deterioration of instrument components Maintenance overdue Improperly performed maintenance or component replacement Calibration time exceeded/overdue Environmental changes (temp, humidity)
False rejection
%5 of control values will fall out of range even if the method is performing properly
If using 2 control levels, false rejection rate is
10% Add 5% per extra control level
Multi rule QC
approach to minimize change of false rejecting while still maintaining high levels of error detection Ex. Westgard Rules
Rule violation within run
a rule violation with a) only one single run of a control level b) within one run of different control levels ran at the same time
Rule violation across runs
a rule violation occurring over more than one run of a control level (or levels)
Rule violation within controls (control levels)
a rule violation by only one level of control
Rule violation across controls
a rule violation including 2 different levels of control
