1. Quality Control Lecture 3
Quality Assurance 2
Quality Control
Lecture 3

2. What is Quality Control?
Quality Control in the clinical laboratory is a system designed to increase the probability that each result reported by the laboratory is valid and can be used with confidence by the physician making a diagnostic or therapeutic decision.

3. Quality Control Programs
The goal of a well-defined QC system is to detect immediate errors in an analytical run while minimizing the number of false rejections.
The simplest type of QC procedure uses one rule to reject the analysis based on QC results falling outside of a range such as the 95% range.
These facts are based on probability that the correct decision was made 95% of the time when results that fall within this range are accepted.

4. Control Of The Analytical Quality Using Stable Control Materials
The performance of analytical methods can be monitored by analyzing specimens whose concentrations are known and then by comparing the observed values with known values.
The known values are usually represented by an interval of acceptable values, or upper and lower limits for control (control limits)
When the observed values fall within the control limits – analysis is working properly
When the observed value fall outside the control limits the analyst should be alerted to the possibility of problems in the analysis.

5. Control Of The Analytical Quality Using Stable Control Materials
QA includes analyzing known samples called quality control (QC) samples along with unknown (patient) samples to test for analytical problems.
When QC samples do not produce accurate and precise results, it can be assumed that any patient results obtained at the same time are also erroneous.
Following a set of guidelines for acceptance or rejection of patient results based on the QC results helps to assure reliability of the analysis.

6. Standards and Controls
A substance that has an exact known value and that, when accurately measured, can produce a solution of an exact concentration
Not usually used on a daily basis
Used to calibrate new instruments, recalibrate instruments after repair, at manufacturer’s recommended intervals, or if a method is out of control

7. Control
A solution that contains the same constituents as those being analyzed in the patient sample
Most are commercially produced from pooled sera
The manufacturer has analyzed each lot of serum for a variety of test components and the expected range of assay values for each component is provided to the laboratory when shipped

8. Control
Controls are analyzed with each patient test or batch of tests and the results are compared with the manufacturer’s range of values
For most tests, a “normal” control and an “abnormal” control are analyzed with each patient test or batch of tests
Results are plotted on a QC record called a Levey-Jennings Chart

9. Quality control (QC) procedures
Quality control (QC) procedures function by detecting analytical errors;
ideally any error large enough to invalidate the medical usefulness of laboratory results should be detected.
The measurement of QC samples will detect problems of precision and accuracy over time.
Interpretation of control results is based on using specific rules for acceptance and rejection of QC results, documenting results and decisions, and having a process for resolving problems that result in rejection of results.

10. Gaussian Probability Distribution
It is very important in statistics
When the distribution of values around the mean are plotted graphically and are symmetrical this is referred to as a Gaussian curve.
Statistical procedures are based on Gaussian probability distribution.

11. Rule
In a random distribution and in a correctly operating test system approximately:
68% of the values will be between the ± 1s ranges and will be evenly distributed on either side of the mean
95% of the values should fall between the ± 2s ranges
and 99% between the ± 3s limits
This means that one data point in 20 should be placed between either of the 2s and 3s limits
One data point placed outside of the 3s limits will occur once in 100 analyses

13. How Are These Values Used?
Mean and SD are calculations that assess the accuracy and precision of the analysis statistically.
Errors of accuracy may be assessed by examining changes in the measured concentration of the control over time and comparing these concentration values to mean and SD ranges of the control.
By contrast, an imprecision problem will be demonstrated by an increase in the SD and %CV of results of the control concentration over time.

14. General Principles Of Control Charts
Control charts are simple graphical displays in which the observed values are plotted versus the time when the observations are made.
The control limits are calculated from the mean (x) and standard deviations (s)

15. General Principles Of Control Charts
The most commonly used charts indicate day or run number on the X-axis and observed QC concentration, indicating mean, and SD ranges on the Y-axis
One example of a QC chart is the Levey-Jennings control chart.
By plotting the daily QC results, one can visualize the deviation of the results from the mean, typically noting when the results are greater than 2 SD from the mean on a daily basis.

16. Control Rules
The criteria used to determine acceptability of each control measurement are termed control rules, or QC rules.
Westgard defined QC rules based on the earlier work of Shewhart, Levey, and Jennings.
Use of multiple control rules (commonly referred to as Westgard rules) can improve the performance of the control system.

17. Control Rules
Individual rules have different capabilities for detecting different types of analytical error.
A control rule or control decision is used to judge whether analysis is performing well.
Ranges can be tighter if clinical requirements are more demanding, but the SD limit should not be set so narrow that excessive time and resources are wasted checking false rejections.

20. . 20

21. Errors in Laboratory Testing
Random or Systematic
Random Errors – cannot be absolutely identified (Ex. Differences in techniques between workers, specimen characteristics, etc.) - precision
Systematic Errors – variation that may make results consistently higher or lower than the mean value for a control (Ex. Trouble with the instrument, deteriorated reagents, etc.) - accuracy 21

23. Types of Quality Control
QC can be achieved through:
Internal Quality Control (IQC)
External Quality Assessment (EQA)

24. Internal Quality Control Program
An internal quality control program depend on the use of:
internal quality control (IQC) specimens,
LJ Control Charts,
and the use of statistical methods for interpretation.

25. Impact of Internal Quality Control
Continuous detection and rectification of the Analytical Process.
Reagent-Equipment-Personnel-Specimen
Ensure the degree of both precision & accuracy of your results
Assure the quality and clinical applicability of your laboratory reports
Generate objective evidence of your analytical performance.

26. External Quality Assessment (EQA)
Inter laboratory
Complimentary to IQC
Maintain the long-term accuracy of the analytical process.

27. Impact of External Quality Assessment
Continuous quality improvement
Independent laboratory audit
Objective evidence of a laboratory analytical performance
Assess the results which the laboratory delivers
Encourages the search for the root cause of unacceptable performance.
audit-= مراجعة