Quality Assurance & Quality ControlMLS 4625:Clinical Chemistry I
What makes a good laboratory test?
Quality Assurance Activities•Appropriate use of statistics •Proper Instrument Calibration •Appropriate Quality Control –Internal QC –External QC (proficiency testing) •Identifying analytical and diagnostic utility of an assay •Determining reference ranges •Assuring staff competency •Assessing differences between methods •Assessing analytical measuring range (linearity) •Documentation: –Troubleshooting analytical errors –Resolving non-analytical errors –Performing Preventative Maint. on instruments
Use of Statistics in the Laboratory•Before we can talk about quality, we need to remember some basic stats routinely used •Stats are used to help assess quality of methods and patient results •Statistics routinely used in the clinical lab –Mean –Standard deviation –Coefficient of variation –Linear regression and correlation coefficients
Mean•The average value of a set of numbers
Standard Deviation()()SDxxn=−−∑21Expresses how disperse the data is from the mean.
Gaussian Curve Std Deviations•Results in a Gaussian curve –68.3% of the results are +/- 1 SD –95.5% +/- 2 SD –99.7% +/- 3 SD
Coefficient of Variation•Compares different sets of observations relative to the mean •The smaller the CV, the more values that are close to the mean •Ideal < 5% for many assays –Some you want tighter, some looser
Equation for CV
Regression and CorrelationHelps describe the relationship between two methods Must know how to interpret slope, y-intercept, and Correlation Coefficient
Instrument Calibration•Standards/Calibrators –Material has a known value of the given analyte •When Performed: –Calibrate new instruments –Recalibrate after repair –Manufacturer’s recommendations •Reagent do deteriorate to an acceptable degree •Recalibrating accounts for this anticipated deterioration –Test method out of control •Do NOT jump to this!
Types of Standards•Primary Standard –Extremely pure substance –Tough to come by in the clinical laboratory •Secondary Standard –Prepared in a laboratory for a specific analysis and compared to a primary standard to assure reference value is correct
Quality Control•Purpose: –Ensures patient results are reliable –Reliable = accurate and precise results •Accuracy –How close is the result to the true result?