Quality Control Flashcards
a system of ensuring accuracy and precision in the lab by including quality control reagents in every series of measurements
Quality Control
process of monitoring the characteristics of the analytical processes and detects analytical errors during testing and prevent the reporting of inaccurate patient test results
Quality Control
ability of an analytical method to measure the smallest concentration of the analyte interest
sensitivity
ability of an analytical method to measure only the analyte of interest
specificity
- nearness or closeness of the assayed value to the true or target value
- estimated using 3 types of studies: recovery, interference and patient sample comparison
- recovery study determine how much of the analyte can be identified in the sample
accuracy
ability of an analytical method to give repeated result on the same sample that agree with one another
precision or reproducibility
the degree by which a method is easily repeated
practicability
ability of an analytical method to maintain accuracy and precision over an extended period of time during which equipment, reagents, and personnel may change
reliability
- involves the analyses of control samples together with the patient specimens
- detects changes in performance between the present operation and the stable operation
- important for the daily monitoring of accuracy and precision of analytical methods
Intralab Quality Control
- involves proficiency testing programs that periodically provide samples of unknown concentrations to participating clinical laboratories
- important in maintaining long-term accuracy of the analytical methods
- also used to determine state-of-the-art interlaboratory performance
- College of American Pathologist (CAP) proficiency program is the gold standard for clinical laboratory external QC testing
interlab quality control
- A series of unknown samples are sent to the laboratory from the reference laboratory
unauthorized program provider. - Unknown samples must be tested by the laboratorians who regularly perform analysis of patient specimens using the same reagents and equipment for actual patient specimens and the results are submitted to the program provider, preferably as soon as every analysis is done.
- Analysis of the unknown samples should be completed within the usual time as for the routine samples.
- Unknown samples should be treated like a patient specimen to determine the true essence of
accuracy.
conducting the external QC testing
- The accuracy of any assay depends on the control solutions, how they are originally constituted, and how they remain stable over time.
- General chemistry assays used 2 levels of control solutions, while immunoassays used 3 levels.
- To establish statistical quality control on a new instrument or on new lot numbers of controL
materials, the different levels of control material must be analyzed for 20 days.
Control Solutions (QC Materials)
- These are expected values represented by intervals of acceptable values with upper
and lower limits. - If the expected (control) values are within the desired control limits, the clinicians are
assured that the test results are accurate and precise. - Control limits are calculated from the mean and standard deviation (SD).
- The ideal control/reference limit is between +/-2SD.
Control Limits (Control Values)
errors encountered in the collection, preparation, and measurements of samples including transcription and releasing of lab results
Variations
- present in all measurements; due to chance.
- type of error which varies from sample to sample
- due to instrument, operator and environmental conditions
random error
- an error that influences observations consistently in 1 direction (constant difference)
- detected as either a positive or negative bias
systematic error
- refers to a difference between the target value and the assayed value
- independent of sample concentration
- exists when there is a continual difference between the comparative method and the test method regardless of the concentration
constant error
- results in greater deviation from the target value due to higher sample concentration
- exists when the difference between the test method and the comparative method values is proportional to the analyte concentration
proportional/slope/percent error
- highest frequency of clerical errors occurs with the use of handwritten labels and request forms
clerical error
the science of gathering, analyzing, interpreting and presenting data
statistics
- a measure of central tendency.
- associated with symmetrical or normal distribution
mean
- a measure of the dispersion of values from the mean
- helps describe the normal curve
- a measure of the distribution range
- most frequently used measure of variation
standard deviation
a percentile expression of the mean; an index of precision
coefficient or variation
called the standard deviator squared; measure of variability
variance
used to compare the means or standard deviations of without group of data
inferential statistics
used to determine whether there is a statistically significant difference between the standard deviations of 2 groups of data
f-test
- value of the observation that divides the observations into two
groups, each containing an equal number of observations. - It is the midpoint of a
distribution; 50th centile
median
- most frequent observation;
- used to describe data with two centers (bimodal).
mode
- simplest expression of spread or distribution
- difference between the highest and lowest score in a data
range
difference between the value of a data point and the mean value divided by the group’s SD
Standard deviation index
- used to observe values of control materials over time to determine the reliability of the analytical method
- utilized to observe and detect analytic errors such as inaccuracy and imprecision
quality control chart
- occurs when the data set can be accurately described by the SD and the mean
- obtained by plotting the values from multiple analyses of a sample
- a population probability distribution that is symmetric about the mean
- occurs when data elements are centered around the mean with most elements close to the mean
- focuses on the distribution of errors from the analytical method rather than the values from a healthy or patient population
gaussian curve (bell-shaped curve)
- calculate the difference between QC results and the target means
- identifies consistent bias problems; requires computer implementation;
- very sensitive to small, persistent errors that commonly occur in the modern, low calibration-frequency analyzer
results are out of control when the slope exceed 45 or a decision
cumulative sum graph
- used to compare results obtained on a high and low control serum from different laboratories
- displays the results of the analyses by plotting the mean values for 1 specimen on the x-axis and y-axis
youden/twin plot
- most widely used QC chart in the clin lab
- allows the laboratorians to apply multiple rules w/o the aid of a computer
- graphic representation of the acceptable limits of variation in the results of an analytical method
shewhart levey-jennings chart
formed by control values that either increase or decrease for six consecutive days.
trend
- It is formed by control values that distribute themselves on one side or either side of the
mean for six consecutive days. - reference range is due to transient instrument
differences.
shift
- control values that are far from the main set of values. These are highly deviating values.
- caused by random or systematic errors.
outliers
- recognizes that the use of simple upper and lower control limits is not enough to identify
analytical problems. - error detection rates can increase without increasing the false rejection rate.
- used the term control rule to indicate fi the analytical process si out of control.
westgard control chart
- a performance improvement program, in which the goal is to improve the process by
eliminating variations or errors: improved performance, improved quality, improved bottom line,
improved customer satisfaction, and improved employee satisfaction. - a tool that can be used to reduce laboratory errors, increase productivity and improve
quality in the clinical laboratory. - measures the degree of variability or error in products or services through statististics and
quantitative parameters - process defects or errors are analyzed, potential causes are
identified, and improvements are implemented.
six sigma
- a system for reducing waste (“non-valued activities”) especially in production or
manufacturing processes. - was conceptualized to improve the automobile industry in terms of the quality and efficiency
of automobile production. - systems to diminish costs by identifying daily work activities that do not directly add to
the delivery of laboratory services in the most efficient or cost-effective ways. - focuses on work flow actions in performing specific tasks, procedures, or other activities
accomplished by critically reviewing each step in the process to determine where inefficiencies
can be eliminated.
lean system
- a set of control and patient specimens assayed, evaluated and reported together.
Analytical Run
- most commonly used patient based-QC technique.
- requires computerization of test data so that current results can be compared with past results.
- difference between two consecutive measurements of the same analytes on the same individual.
delta check
- used to measure systematic errors or inaccuracy caused by substances other than the analyte
- hemoglobin, lipids, bilirubin, anticoagulants and preservatives
Interference experiments
- the concentration range over which the measured concentration is equal to the actual concentration
without modification of the method.
Linear Range/Dynamic Range
helps detect sample contamination or dilution, inadequate sample volume, inadequate reageni volumes,
sudden major problems with the method, or incorrect recording or transmission of the result.
Physiologic Limit
- a type of analytical testing performed outside the confines of the central laboratory, usually by non-laboratorian personnel (nurses, respiratory therapists, etc).
- use of portable whole blood glucose meters for the management of patients
with diabetes mellitus.
Point Of Care Testing (POCT)/Decentralized Testing
a systematic action necessary to provide adequate confidence that laboratory services will satisfy the given medical
needs for patient care.
Quality Assurance (QA)
includes effective test request forms, clear instruction for patient preparation and specimen handling, appropriate
turn-around time for specimen processing, testing and result reporting, appropriate reference ranges and intelligent
result reports.
Quality Patient Care
shows whether a method measures al the analytes or only part of it. It also estimates inaccuracy or systematic error.
Recovery experiment
depends on sensitivity, specificity, and prevalence of the disease being test.
Predictive value
probability that a positive test indicates disease; it is the proportion of persons with a positive test who truly have
the disease.
Positive predictive value
probability that a negative test indicates absence of disease. It is the proportion of people with a negative test
who are truly without disease.
Negative predictive value
