LESSON 3: QUALITY CONTROL Flashcards
QC in the laboratory involves the systematic monitoring of _____ to detect _____
analytic processes, analytic errors
Specimens analyzed for QC purposes are known as
QC materials
QC materials must be available in sufficient quantity to last for extended periods of time determined by
QC material stability and vendor determined expiration dates
PARAMETERS OF QUALITY CONTROL: (7)
- Sensitivity
- Specificity
- Accuracy
- Precision or Reproducibility
- Reliability
- Diagnostic Sensitivity
- Diagnostic Specificity
it is the ability of an analytical method to measure the smallest concentration of the analyte of interest
Sensitivity
it is the ability of an analytical method to measure only the analyte of interest
Specificity
the nearness or closeness of the assayed value to the true or target value.
Accuracy
the ability of an analytical method to give repeated results on the same samples that agree with one another.
Precision or reproducibility
the ability of an analytical method to maintain accuracy and precision on the extended period of time.
Reliability
it is the ability to detect the proportion of individuals with the disease who test positively with the test.
Diagnostic sensitivity
Diagnostic sensitivity (%) Formula
100 x number of diseased individuals / total number of individuals tested w/o the disease
Diagnostic specificity (%) Formula
100 x the number of individuals without the disease with a negative test / total number of individuals tested w/o the disease
Kinds of Quality Control:
- Intralab (internal QC)
- Interlab (external QC)
Involves the analyses of control samples together with the patient specimens. It detects changes in the performance between the present operation and the stable operation. It is important for the daily monitoring accuracy and precision of analytical method
Intralab (internal QC)
Intralab detects both ___ and ___ errors
random and systematic errors
It involves proficiency testing programs that periodically provide samples of unknown concentration of analytes to participating laboratories.
it is important in maintaining long-term accuracy of the analytical methods
Interlab
Objectives of quality control:
- To check the stability of the machine
- To check the quality of reagents
- To check the technical errors.
Characteristics of an ideal QC Material
- Resembles human sample
- Inexpensive and stable for long periods
- No communicable disease
Quality Control bottle cap COLOR for ABNORMAL LOW
Blue
Quality Control bottle cap COLOR for ABNORMAL HIGH
Red or Black
Quality Control bottle cap COLOR for NORMAL
Green or White
Sources of QCM:
- In-house QCM
- Commercial QCM
In-house QCM are usually from ____ or ____
Human or Bovine (Cow)
In-house QCM, 3 types
- Pooled sera
- Fasting donor sera
- Blood bank plasma
Pooled sera is describes as ___ sera
Left over sera
Pooled sera is froze for ___ hours at ___ °C
72h at -20°C
Pooled sera is allowed to thaw at __°C for __ hours
6°C for 16 hours
Pooled sera is not for
- Not for immunochemistry assays – some bovine protein differs from human
- Not for dye-binding procedures for albumin
2 types of Commercial QCM
- Lyophilized form
- Non-lyophilized form (liquid)
Pooled sera has specific temperature and time to kill ____
bacteria
Lyophilized form: ___°C; freezing (best storage); shelf life: ___ hrs.; preparation:
2-8°C;24 hrs
Lyophilized form is stored in an _____ due to its sensitivity to light
amber bottle
Lyophilized form is diluted with ____
distilled water
If non-lyophilized form has jelly, it is ____
contaminated
it is important for non-lyophilized form to be clear, serum color, and for its ___ part to be checked
bottom part
true or false. Non-lyophilized form from refregirator can be used right away
false, it must be room temp
Commercial QCM that is in liquid form
Non-lyophilized form
VARIATIONS IN QUALITY CONTROL
- Random Error
- Systematic Error
- Clerical Error
In determining error or imprecision. It is the basis of varying differences between repeated measurements.
Random error
Random error is due to
instrument, operator and environmental conditions
Random error. Variation techniques:
Pipetting error
Mislabeling of samples
Temperature fluctuations
Improper mixing of samples and reagents
Inaccuracy.It is an error that influences observations consistently in one direction. It detects positive and negative bias, often related to calibration problem, inadequate reagent blanks, leaky ISE, failing instrumentation and poorly written procedure.
Systematic error
The highest frequency of this error occurs with the use of a handwritten labels and request forms.
Clerical error
a measure of central tendency. It is associated with symmetrical or normal distribution. It measures accuracy or system error.
Mean
is calculated by summing the observations and dividing by the number of the critically evaluated observations.
Mean
a measure of the dispersion of values from the mean. It helps describe the normal curve. It measures precision or random error. the most frequently used measure of variation
Standard deviation
where the numbers that you need to calculate are the entire population./ parameters ,fixed value
Population SD
calculated from only some of the individuals in a population./ statistics
Sample SD
it is called standard deviation squared; a measure of variability
Variance
it is the value of observation that divides the observation into two groups, each containing equal number of observations
Median
it is the most frequent observation.
Mode
it is used to determine whether there is a statistical significant difference between the means of two groups of data.
T – test
it is used to determine whether here is statistically significant difference between the standard deviations of two groups of data.
F – test
graphically represent the observed values of a control material over time in the context of the upper and lower control limits in relation to the target value.
Control charts
_____ in the clinical laboratory is used to monitor the analytic variations that can occur
QC system
The QC program can be thought of as a three-stage process:
- Establishing or verifying allowable statistical limits of variation
- Using these limits as criteria for evaluating the QC data generated for each test
- Acting to remedy errors real time when indicated
a. Finding the cause(s) of error
b. Taking corrective action
c. Reanalyzing control and patient data
TYPES OF QC CHARTS
- Gaussian curve
- Cumulative sum graph
- Youden/ twin plot
- Shewhart Levey-Jennings chart
Type of chart that is used to visualize accuracy and precision
It occurs when the data set can be accurately described by the SD and the mean. It focuses on the distribution of errors from the analytical method rather than the value from a healthy or patient population
Gaussian curve
Type of chart that calculates the difference between QC results and the target means.
The most common method is the V-mask; require computer implementation
It identifies consistent bias problems.
Cumulative sum graph
It is used to compare results obtained on a high a low control serum from different laboratories
Youden/ twin plot
Most widely used QC chart in the clinical laboratory
It allows the laboratories to apply multiple rules without the aid of a computer.
Shewhart Levey-Jennings chart
Errors which can be observed on LJ chart:
Trend
Shift
Outliers
It is a gradual lost of reliability, formed by control values that either increase or decreased for six consecutive days
Main cause: deterioration of reagent
Trend
Trend. Main cause:
deterioration of reagent
it is formed by control values that distribute themselves on one side or either side of the mean for six consecutive days
Shift
Shift. Main cause:
improper calibration of the instrument
In Shift, __ or more consecutive data points are either all above or below the median constitute
6
In Trend, __ data points are all going up or down constitutes
5
These are control values that are far from the main set of values
Outliers
Outliers. Main cause:
random or systematic errors
It recognized the use of simple upper and lower limits are not enough to identify analytical problems
Westgard control rules
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.
13s
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.
12s
reject when 2 consecutive control measurements exceed the same mean plus 2s or the same mean minus 2s control limit.
22s
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.
R4s
reject when 4 consecutive control measurements exceed the same mean plus 1s or the same mean minus 1s control limit.
41s
reject when 10 consecutive control measurements fall on one side of the mean.
10x
reject when 8 consecutive control measurements fall on one side of the mean.
8x
reject when 2 out of 3 control measurements exceed the same mean plus 2s or mean minus 2s control limit;
2of32s
- reject when 3 consecutive control measurements exceed the same mean plus 1s or mean minus 1s control limit
31s
reject when 6 consecutive control measurements fall on one side of the mean.
6x
reject when 9 consecutive control measurements fall on one side of the mean.
9x
______ is another tool in the ongoing process of monitoring test performance
proficiency testing
Acceptable performance in ______ is required by the CAP, the CLIA, (Clinical Laboratory Improvement Amendments and the College of American Pathologists)
proficiency testing programs
Method used to validate a particular measurement process. The results are compared with other external laboratories to give an objective indication of test accuracy.
Proficiency test
Specimens that have known concentrations of an analyte for the test of interest. The testing laboratory does not know the targeted concentration when tested
Proficiency samples
is one of the measures by the Department of Health (DOH) to assess the reliability of laboratory diagnosis and maintain quality assurance of licensed clinical chemistry laboratories in the country.
The National External Quality Assessment Scheme (NEQAS)
Variations in QC: No error = ?
✔ accuracy
✔ precision
Variations in QC: Random error = ?
✔ accuracy
✘ precision
Variations in QC: Systematic error = ?
✘ accuracy
✔ precision
