Lesson 3.pptx

QUALITY ASSURANCE Includes all the steps to ensure accurate, precise and timely results for the patients. Laboratory's system for recognizing and minimizing analytical error 3 phases:  Pre-Analytical-patient preparation, specimen collection, transport and storage  Analytical - condition...

QUALITY ASSURANCE Includes all the steps to ensure accurate, precise and timely results for the patients. Laboratory's system for recognizing and minimizing analytical error 3 phases:  Pre-Analytical-patient preparation, specimen collection, transport and storage  Analytical - condition of reagents/equipment, pipetting, QC, personnel competency  Post-Analytical-reporting of results, timely releasing of results, record keeping Materials used to maintain accuracy/precision of Lab equipment: Control  Resembles test specimen (patient-like material) Contains several known analyte concentrations Monitors precision of test system CLIA requires at least 2 levels of controls (HIGH and LOW) Calibrator Formerly known as "standard" Usually contains one analyte Tests and adjusts instrument program to measure the concentration of unknown  Kinds of Quality Control Internal QC (Intralab)  Involves analyses of control samples within the Lab  Daily monitoring of accuracy/precision of analytical methods External QC (Interlab)  Involves participation in proficiency testing programs  Long-term monitoring of accuracy of analytical methods IMPORTANT TERMS 1. Accuracy - closeness of result to true value 2. Precision - closeness of replicates; reflects degree of reproducibility 3. Reliability -ability to maintain accuracy & precision over an extended period of time; Consistent 4. Delta Check-comparison of patient data with their previous results 5. Reference Range - formerly called Normal value; established by testing minimum of 120 healthy subjects & determining range in which 95% fall.  Method Evaluation 1. Analytical Sensitivity- ability of a method to detect SMALL QUANTITIES of an analyte. 2. Analytical Specificity-ability of a method to detect ONLY the analyte it is designed to determine  Measures of Diagnostic Efficiency 1. Clinical Sensitivity -Percentage of persons with the discase who have a positive test result Formula: T P /(T P + F N) X 1 0 0 2. Clinical Specificity -Percentage of persons without the disease who have a negative test result. Formula: : T N/(T N + F P) X 100  Measures of Diagnostic Efficiency 3. Positive Predictive Value- Probability of an individual having the disease if the result is abnormal or outside the reference range. Formula: : T P/(T P + F P) X l00 4. Negative Predictive Value - Probability that a patient does not have a disease if the result is normal or within the reference range Formula: T N/(T N + F N) X1 0 0 Gaussian Distribution  A symmetrical bell-shaped curve generated when we plot the assay of a reliable method used for measuring an analyte. (Johann Karl F. Gauss)  Assay values obtained are plotted on the x axis, & their elative frequency on the y axis  Measures of Central Tendency Mean  The PEAK of the Gaussian curve indicates the mean value for a data set  It is the AVERAGE of all the values in a data set Median  Midpoint observation  If there is even number of values, the median is the average of the 2 innermost values Mode  It is the most frequent observation Mean = Median = Mode  Measures of Dispersion 1. Range - difference between highest & lowest values in data a set 2. Variance - average distance from the center (mean) and every value in a data set 3. SD - square root of variance; most frequently used measure of variation 4. CV - also known as Relative Standard Deviation; expresses standard deviation as percentage S D / C V = index of analytical precision (↓ CV = results in HIGH PRECISION)  Two Components of Measurement (observation) Error 1. Random Error (indeterminate error)  Due to chance; affects PRECISION Ex: mislabeling a sample, variations in technique, pipetting error, voltage fluctuations. 2. Systematic Error (determinate error)  consistent changes in one direction  usually seen as a TREND (gradual increase or decrease) Ex: deterioration of reagents; poorly prepared calibrators, sample instability; dirty photometer  Two Components of Measurement (observation) Error 2 Types of Systematic Error: 1. Constant error - difference between 2 test methods is constant regardless of concentration. 2. Proportional Error - difference between 2 test methods is proportional to concentration  Inferential Statistics T test - used to compare two related means F-test - used to compare two SD (variances)  Quality Control Charts 1. Levey-Jennings / Shewhart  Most widely used chart in the laboratory  Involves analysis of control sample over a period of 20 consecutive days 2. Youden plot  graphical method to analyze interlaboratory data, where laboratories have analyzed two control specimens (low & high controls), for the same analyte.  Can help differentiate random and systematic error  Quality Control Charts 3. CUSUM graph  used in the laboratory which requires computer implementation it is very responsive to systematic error & sensitive to small, persistent shifts that commonly occur in the modern, low- calibration-frequency analyzer.  monitor the deviation from the target value (CUSUM chart is an alternative to Shewhart control charts)  Westgard Control Rules the “control rules” utilized to indicate the criteria for judging out- of-control situations 12s refers to the control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus/minus 2s. In the original Westgard multirule QC procedure, this rule is used as a warning rule to trigger careful inspection of the control data by the following rejection rules. 13s refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit. 22 s - reject when 2 consecutive control measurements exceed the same mean plus 2s or the same mean minus 2s control limit. R4s - reject when 1 control measurement in a group exceeds the mean plus 2s and another exceeds the mean minus 2s. This rule should only be interpreted within-run, not between-run. The graphic below should really imply that points 5 and 6 are within the same run. 41s - reject when 4 consecutive control measurements exceed the same mean plus 1s or the same mean minus 1s control limit. ADDITIONAL 10x - reject when 10 consecutive control measurements fall on one side of the mean. 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. 2of32s - reject when 2 out of 3 control measurements exceed the same mean plus 2s or mean minus 2s control limit 31s - reject when 3 consecutive control measurements exceed the same mean plus 1s or mean minus 1s control limit. 6x - reject when 6 consecutive control measurements fall on one side of the mean. 9x - reject when 9 consecutive control measurements fall on one side of the mean. 7T - reject when seven control measurements trend in the same direction, i.e., get progressively higher or progressively lower.  Westgard Rule that alerts the technologist (WARNING) for possible further violations: 12s  Westgard Rules Effective in Detecting Random Error: 13s, R4s  Westgard Rules Effective in Detecting Systematic Error: 22s, 41s, 10x SHIFT  sudden/abrupt change in the analytical process  6 consecutive control values on same side of mean  Most common cause: ERROR IN CALIBRATOR PREPARATION  Upward shift: less concentrated calibrator  Downward shift: too concentrated calibrator TREND  gradual change in the analytical process  6 consecutive control values constantly increasing /decreasing  Most common cause: DETERIORATION OF REAGENTS THANK YOU!