Quality Control Flashcards
A part of Quality assurance program (internal quality control).
It evaluates the validity of laboratory results before reporting.
Aims to identify and correct errors to ensure accuracy and precision.
QUALITY CONTROL (QC)
refers to closeness of measured value of an analyte to its true value.
ACCURACY
Also known as detection limit.
The lowest concentration of substance that can be detected by test method.
High sensitivity decrease false (-)
Desirable for screening test
Analytical sensitivity
proportion of population with disease who will be positive for result.
Also known as true POSITIVE RATE.
Diagnostic sensitivity
the degree of closeness or agreement among values between repeated measurements.
PRECISION/REPRODUCIBILITY
Ability of test method to measure only the target analyte and not the other related substances.
High specificity decreases false (+) and cross reactivity.
Desirable for confirmatory test.
Analytical specificity
proportion of population without disease who will be negative for result.
Also known as TRUE NEGATIVE RATE.
Diagnostic specificity
a set of values with upper and lower limits based on a healthy individual (120 person).
REFERENCE interval (normal values)
Use to compared with patient value for laboratory interpretation.
REFERENCE interval (normal values)
Also known as LINEARITY.
Reportable range
Range of values over which lab can verify accuracy of the test system.
Provided by the manufacturer and verify by testing 20 normal samples.
Reportable range
comparison of patient data with previous result (24-48 hours interval). It determine if the changes is due to medical or lab error.
Delta check-
test value that considered as life threatening. Glucose, electrolytes, total bilirubin and blood gases are list typically. Immediate notification to health care personnel should be done.
Critical values-
Internal quality control
Part of analytical phase of QA
the testing of control together with the patient sample.
Monitors the accuracy and precision of analytical method on a daily basis and detects any error
Intralab QC
External quality control
Testing of proficiency sample with unknown concentration.
Participated by different laboratories.
Maintain long term accuracy of the analytical method.
The gold standard for proficiency testing is the College of American pathologist (CAP).
Interlab QC
check the stability of the instrument/machine, quality of reagent, and technical error.
Quality control
a solution with precise known concentration used to identify and determine the concentration of the sample. Not serum or plasma based
STANDARD
a solution or device with known concentration or activity that is used to calibrate, adjust , or graduate measurement of an instrument to match a known input. Serum or plasma based.
CALIBRATOR
a patient-like material made from human serum.
Used to run with patient samples.
Used to monitor the performance of an instrument after calibration.
Measure precision/reproducibility
Control
used to evaluate overall precision of 2 different methods or instruments and reagents.
COEFFICIENT VARIATION
used in external quality assessment program or a proficiency testing program.
Standard deviation index
Types of Quality control chart
Gaussian normal distribution graph
Cumulative sum graph
Youden/twin plot
Shewhart Levey-Jennings chart
Population probability distribution that is symmetric about the mean.
Also known as normal distribution curve.
Gaussian curve ( bell shape curve)
It identifies the consistent problem and requires computer for implementation.
Cumulative sum graph (CUSUM)
This plot is indicator of systemic error (trend) and can be used with the 1s rule.
Results are out of control when slopes exceeds 45 degrees.
Cumulative sum graph (CUSUM)
The most widely used QC chart
Illustrate the overall distribution of QC values for interpretation.
Used to graph successive/ day to day control values. At least 20 measurements
Shewhart Levey-Jennings chart
Used to compare results obtained on a high and low control serum from different laboratories.
Display the results of the analyses by plotting the mean value for one specimen on the y-axis and the other specimen for x-axis.
Points falling at the center within a 45 degree line- proportional error.
Points falling at center outside of 45 degree- constant error
Youden/twin plot
a representation of vertically oriented Gaussian curve.
Shewhart Levey-Jennings chart
approximation of distribution within a normal distribution.
Empirical Rule
the midpoint or middle value of a distribution. To determine arrange the data in numerical order (ascending order).
Median
is the frequent observation in a data set.
Mode
expression of spread or distribution. To determine subtract the highest data to lowest data.
Range
sudden change in data for several days. 6 or more consecutive values are observed only on one side of the mean. The main cause is improper calibration of instrument.
Shift (bias)-
6 or more values move continuously in one direction. Hard to notice because it looks like a shift. Main cause is reagent deterioration.
Trend
Any value outside established limit (+/-3s). It is significant if occurs more than once in 20 successive runs, caused by systematic or random error.
Outlier
Uses two or more control rules to evaluate the QC data, and then rejects a run if any one of these is present.
Multi rule system
a single value is outside ±2s limits. Indicate a systematic or random error.
12s
any value outside ±3s limits. Indicates a random error
13s
there is at least 4 differences between control values within a single run. Indicates a random error only.
R4s
2 consecutive values outside the ±2s limits. Indicates systemic error.
22s
3 consecutive values outside ±1s limits. Systematic error
31s
4 consecutive values outside ±1s limits. Systematic error
41s
10 control results on the same side of the mean regardless of SD which they are located. Systematic error.
10x
