CC (quality control)
13S Rule
If 1 control observation exceeds x ± 3s, reject the run for probable random error
10xRule
If 10 consecutive control values fall on 1 side of x (either + or -), reject the run for probable systematic error
22S Rule
If 2 consecutive control values are greater than x + 2s or x - 2s, reject the run for probable systematic error.
41S Rule
If 4 consecutive clues exceed the same x + 1s or x - s limit, reject the run for probable systematic error.
Random Error
It is due to instrument, operator and environmental conditions (variations in techniques)
Intralab (Internal QC)
It is important for the daily monitoring of accuracy and precision of analytical methods.
Interlab(External QC)
It is important in maintaining long-term accuracy of the analytical methods.
Constant Error
It is independent of sample concentration.
Gaussian Curve (Bell-Shaped Curve)
It is obtained by plotting the values from multiple analyses of a sample.
Youden/Twin Plot
It is used to compare results obtained on a high and low control serum from different laboratories
Gaussian Curve (Bell-Shaped Curve)
It occurs when data elements are centered around the mean with most elements close to the mean.
Gaussian Curve (Bell-Shaped Curve)
It occurs when the data set can be accurately described by the SD and the mean.
Westgard Control Rules
It recognized that the use of simple upper and lower control limits are not enough to identify analytical problems.
Diagnostic Specificity
It reflects the ability of the method to detect true-negatives with very few false-positives.
Shewhart Levey-Jennings Chart
A graphic representation of the acceptable limits of variation in the results of an analytical method.
Gaussian Curve (Bell-Shaped Curve)
A population probability distribution that is symmetric about the mean
Outliers
Are caused by random or systematic errors.
Outliers
Are control values that are far from the main set of values.
Intralab (Internal QC)
Detects both random and systematic errors.
Youden/Twin Plot
Displays the results of the analyses by plotting the mean values for one specimen on the ordinate and the other specimen on the abscissa.
Westgard Control Rules
Error detection rates can increase without increasing the false rejection rate.
Proportional/Slope/Percent Error
Exists when difference between the test method and the comparative method values are proportional to the analyte concentration.
12S Rule
If 1 control observation exceeds x ± 2s, A warning rule.
R4S Rule
If the difference between the 2 controls is equal to or greater than 4s, reject the run for probable random error.
Diagnostic Sensitivity
Indicates the ability of the test to generate more true-positive results an few falsenegative.
Systematic Error
Is an error that influences observations consistently in one direction (constant difference)
Shift
Is formed by control values that distribute themselves on one side or either side of the mean for six consecutive days
Trend
Is formed by control values that either increase or decrease for six consecutive days
Quality Control
Is one component of the quality assurance system.
Random Error
Is present in all measurements; it is due to chance.
Random Error
Is the basis for varying differences between repeated measurements.
Shewhart Levey-Jennings Chart
It allows the laboratorians to apply multiple rules without the aid of a computer.
Cumulative Sum Graph (CUSUM)
It calculates the difference between QC results and the target means.
Intralab (Internal QC)
It detects changes in performance between the present operation and the stable operation.
Constant Error
It exists when there is a constant difference between the comparative method and the test method regardless of the concentration.
Gaussian Curve (Bell-Shaped Curve)
It focuses on the distribution of errors from the analytical method rather than the values from a healthy or patient population.
Interlab(External QC)
It involves proficiency testing programs that periodically provide samples of unknown concentration of analytes to participating laboratories.
Intralab (Internal QC)
It involves the analyses of control samples together with the patient specimens.
Quality Control
It involves the process of monitoring the characteristics of the analytical processes and detects analytical errors during testing.
Systematic error
It is a measure of the agreement between the measured quantity and the true value.
Interlab(External QC)
It is also used to determine estimates of the state-of-the-art interlaboratory performance.
Systematic Error
It is detected as either positive or negative bias; often related to calibration problems deterioration of reagents and control materials, contaminated solutions, unstable and inadequate reagent blanks, leaky ion selective electrode (ISE), failing instrumentation and poorly written procedures.
Trend
MAIN CAUSE: deterioration of reagent
Shift
MAIN CAUSE: improper calibration of the instrument
Shift
More than six consecutive values fall in one side of the mean
Shewhart Levey-Jennings Chart
Most widely used QC chart in the clinical laboratory.
Shewhart Levey-Jennings Chart
Once a rule has been violated, reject the analytic run, take action to remedy errors (find the cause of error, take corrective action, reanalyze control and patient
Constant Error
Refers to a difference between the target value and the assay value.
Cumulative Sum Graph (CUSUM)
Results are out of control when the slope exceeds 45º or a decision (± 2.7 SD) is exceeded.
Proportional/Slope/Percent Error
Results in greater deviation from the target value due to higher sample concentration
Shift
Shift in the reference range is due to transient instrument differences.
Cumulative Sum Graph (CUSUM)
The commonest method is the V-mask; requires computer implementation Identifies consistent bias problems.
Clerical Error
The highest frequency of errors occurs with the use of handwritten labels and request forms.
Youden/Twin Plot
The points falling from a center but on the 45º line suggest a proportional error, and points falling from the center but not on the 45º line suggest a constant error.
Outliers
They are highly deviating values
Cumulative Sum Graph (CUSUM)
This plot will give the earliest indication of systematic errors (trend) and can be used with 13s rule.
22s Rule
This rule identifies systematic error only. The criteria for violation of this rule are: • Two consecutive QC results • Greater than 2s • On the same side of the mean
Cumulative Sum Graph (CUSUM)
Very sensitive to small, persistent errors that commonly occur in the modern, low calibration-frequency analyzer.
Westgard Control Rules
Westgard used the term control rule to indicate if the analytical process is out of control.
Specificity
ability of an analytical method to measure only the analyte of interest.
Sensitivity
ability of an analytical method to measure the smallest concentration of the analyte of interest.
Diagnostic Sensitivity
ability of the test to detect the proportion of individuals with that disease who test positively with the test.
Diagnostic Specificity
ability of the test to detect the proportion of individuals without the disease who test negatively for the disease.
Screening tests
require high sensitivity s that no case is missed.
Confirmatory tests
require high specificity to be certain of the diagnosis.
Precision/Reproducibility
the ability of an analytical method to give repeated results on the same sample that agree with one another.
Reliability
the ability of an analytical method to maintain accuracy and precision over an extended period of time during which equipment, reagents and personnel may change.
Practicability
the degree by which a method is easily repeated.
Accuracy
the nearness or closeness of the assayed value to the true or target value.
