1
Q
- Also known as “Internal Quality Control or Statistical Process Control”
- is a process to periodically examine a measurement procedure to verify that it is performing according to pre-established specifications.
A
Quality Control
2
Q
Clinical Laboratory Test
A
- To evaluate the pathophysiologic condition of an individual patient
- To assist with diagnosis
- To guide or monitor therapy
- To assess risk for a disease or for the progression of a disease.
3
Q
Factors that contribute to TOTAL ERROR
A
- Pre-analytic variability
- Analytic variability
- Interfering substances
4
Q
sample collection, transportation, processing, and storage
A
Pre-analytic variability
5
Q
test performance
A
Analytic variability
6
Q
drugs or metabolic components
A
Interfering substances
7
Q
- Called “QC sample materials”
- are measured periodically in the same manner as clinical samples, and their results are examined to determine that the measurement procedure meets performance requirements appropriate for patient care.
A
Surrogate samples
8
Q
- Dispersion of results
- SD is a measure of expected imprecision in a measurement procedure when it is performing correctly
A
Imprecision
9
Q
- is the difference between the observed mean and the expected value for a QC material.
- If the calibration changes for any reason, a systematic bias is introduced
A
Systematic Bias
10
Q
a method which eliminates systematic bias (within uncertainty limits)
A
-Correct calibration
11
Q
- Closeness of measured value to a standard or known value
A
Accuracy
12
Q
- Refers to the closeness of two or more measurements to each other, regardless of whether those measurements are close to the known value
A
Precision
13
Q
Primary Purpose of Measuring QC Samples
A
- statistically evaluate the measurement process to verify that the method continues to perform within the specifications consistent with acceptable systematic bias and imprecision
- identify that a change in performance occurred that needs to be corrected.
14
Q
The performance of a new method can be assessed for accuracy by _____
A
Assaying patient specimens or interlaboratory survey materials with known values
15
Q
- Used for individual results and is a combination of systematic bias and imprecision that occurred for that specific measurement.
A
Assaying Patient Specimens
16
Q
used to refer to an average systematic bias that may be present in a given method
A
Trueness
17
Q
most often performed by the laboratory using calibrator materials provided by the method or instrument manufacturer
A
Calibration
18
Q
require calibration or calibration verification at least every 6 months, or more frequently if recommended by the method manufacturer
A
Clinical Laboratory Improvement Act (CLIA) regulations, Section 493.1255
19
Q
- component of a quality management system
- part of the process management component of the quality system that integrates good laboratory practices to ensure correct patient results.
A
Statistical Quality Control
20
Q
- required for all aspects of laboratory operation, including statistical quality control
A
Standard Operating Procedures (SOPs)
21
Q
If the QC result is within acceptable limits of the known value
A
the measurement procedure is verified to be stable and results for patient samples can be reported
22
Q
If a QC result is not within acceptable limits
A
the measurement procedure is not performing correctly, results for patient samples are not reported, and corrective action is necessary
23
Q
- also called Shewhart plot (Shewhart, 1931)
- most common presentation for evaluating QC results
A
Levey-Jennings (Levey, 1950)
24
Q
±1 SD
A
68.3% of observations
25
±2 SD
95.4% of observations
26
±3 SD
99.7% of observations
27
QC materials should be selected to
Provide analyte concentrations that monitor the analytic measurement range of the method
28
Common response of quantitative measurement procedures
Linear Response
29
In the case of non-linear method response, it may be necessary to
Use additional controls at intermediate concentrations
30
The QC materials selected must be
Manufactured to provide a stable product that can be used for an extended time period, preferably 1 or more years for stable analytes.
31
Use of a single lot for an extended period allows
reliable interpretive criteria to be established that will permit efficient identification of an assay problem, avoid false alerts due to poorly defined expected ranges for the QC results and minimize limitations in interpreting values following reagent and calibrator lot changes
32
Limitations of Quality Control Materials
o Non-commutable
o Deterioration of the analyte during storage
o Multi-constituent control materials caused by solubility considerations or potential interactions between different constituents, particularly at higher concentrations.
33
Several Parameter for the Frequency to Assay QC Samples
* Analytic stability of the measurement procedure
* Risk of harm to a patient from clinical action being taken before a significant error is detected
* Number of patient results produced in a period of time when an error condition existed but was not yet detected
* Events such as recalibration or maintenance that may alter the current performance condition of the measurement system
* Training and competency of the test operator, particularly for manual or semi-automated methods
* Risk of failure of the measuring device
34
The more stable the system
The less frequently a statistical QC evaluation needs to be performed
35
examine controls at least once per 24 hours, or more frequently if specified by the method manufacturer, or if the laboratory determines that more frequent QC assays are necessary for the performance characteristics of a method
CLIA regulations, section 493.1256 (Department of Health and Human Services, 2003)
36
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EP23 Guidelines
(RISK OF HARM TO A PATIENT AND NUMBER OF PATIENTS WHO MAY BE AT RISK)
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1. how to develop a QC plan based on evaluation of risk of harm to a patient
2. assessment of the effectiveness of risk mitigation procedures using information from the manufacturer and from other sources
3. combined with the clinical requirements of the local health care setting and conditions in the laboratory
37
responsible for ensuring that a result has a high probability to be correct at the time it is reported for clinical use
Laboratory Director
38
* Introduced in the CLIA quality control requirements Survey Procedures and Interpretive Guidelines for Laboratories and Laboratory Services
* Justify less frequent QC for measurement systems that utilized built-in control procedures to monitor various aspects of the measurement process.
Equivalent Quality Control (EQC)
39
New option introduced by the Centers for Medicare and Medicaid Services
Individualized Quality Control Plan (IQCP) in 2014
40
When is it necessary to do an Event-Based Quality Control Sample Assay
Before and After a scheduled event
41
- estimated for a QC material that represents the typical imprecision of the method when it is performing according to its design specifications
- conventional way to express method variability and assumes the QC data can be described by a Gaussian (normal) distribution even though non-Gaussian components of variability influence the QC results
SD
42
• When a method has been established in a laboratory, and a new lot of QC material is being introduced
the target value for the new lot of QC material is used along with the well-established SD from the previous lot.
43
• If target values for the old and new lots are substantially different
a different SD may occur, and adjustment to the SD may be necessary as additional experience with the new lot is accumulated
44
commonly used to assess how well a method performs relative to the medical requirement
Sigma metric
45
compares the variability in a measurement process in standard deviations to the variability that is acceptable because it will not cause an error in diagnosis or treatment of a patient
Sigma scale
46
the sigma metric is calculated as
(TEa − bias ) SD
47
TEa
the total error
48
refer to performance characteristics of the laboratory method
absolute value of bias and SD
49
used to determine if a change in bias has occurred compared to the condition established by calibration of a method
QC Results
50
assumes a Gaussian or normal distribution for repeated measurements
Sigma
51
refers to a condition when the variability in the measurement process is sufficiently smaller than the medical requirement that erroneous results are very uncommon
six sigma
52
less robust and have a higher probability that erroneous results could be produced but still at a fairly low frequency
four sigma
53
produce enough erroneous results even though it met its performance specifications that it would not be very reliable for patient care
two sigma
54
preferred to monitor for bias trends
cumulative sum (CUSUM) or exponentially weighted moving averages (EWMA)
55
used to express the probability that a QC interpretive rule will detect an analytic error of a given magnitude
Power function graphs
56
frequently used to establish acceptance criteria (rules) to evaluate QC results based on data acquired over a long enough time to adequately quantify the expected variability when a method is working correctly
Empirical Judgement
57
does not identify random events (e.g., a temporary clot in a sample pipette, a random reagent pipette error) that do not persist until the next QC sample is measured
Periodic measurement of QC samples
58
Determines that a method's performance is marginal or inadequate to meet medical requirements
process of reviewing statistical parameters for QC data
59
If the method performance cannot be improved and a better method is not available
the laboratory can either discontinue the test if the performance is inadequate or apply more stringent QC practices when the performance is marginal
60
More stringent QC will
NOT improve method performance but is intended to identify smaller changes in method performance that could affect patient care decisions based on the results
61
occurs when a QC result fails an evaluation rule, which indicates that an analytic problem may exist
QC Alert
62
Repeating the QC measurement on the same QC sample is not recommended because,
it is more likely that a measurement system problem exists than the QC result was a statistical outlier
63
When repeat testing of a new QC sample does not resolve the alert situation
the instrument and reagents should be inspected for component deterioration, empty reagent containers, mechanical problems, and so on
64
establish acceptable criteria to determine if the repeat results agree adequately to permit reporting of original results without issuing a corrected report
Laboratory Director
65
determine if patient results can be reported and used for clinical decision making
immediate impact of QC data
66
QC review process two major functions
o It verifies that test procedures are stable and meet performance specifications
o It identifies test procedures that may need intervention to address trends in performance deterioration
67
an opportunity to examine any aspect of assay performance that is relevant for a given measurement procedure to provide results that meet the requirements for clinical care decisions
QC review
68
Why is careful reagent lot crossover evaluation of QC target values is necessary?
Because the matrix-related interaction between a QC material and a reagent can change with a different reagent lot, QC results may not be a reliable indicator of a method’s performance for patient samples following a reagent lot change
69
• The number of patient samples to use for verifying the performance of a new reagent lot will depend on
the imprecision of an assay, and the concentrations at which key clinical decisions are made
70
recommends a minimum of 3 patient samples and possibly more, depending on the number of key clinical decision concentrations and the imprecision of an assay
CLSI document EP26 (CLSI, 2013)
71
The second step for the Assessment of Potential Matrix Impact on QC target values following reagent lot change
- keeps the expected variability centered around the QC target value so that QC interpretive rules will remain valid
evaluation of results for each QC material to determine if its target value is correct for use with the new lot of reagent
72
Failure to make a target value adjustment will
introduce an artifactual bias in subsequent QC results, causing both an increased false alert rate and a decreased ability to detect some error conditions
73
typically performed on a single day and will likely provide only a few QC results from which to evaluate if the target value has changed
reagent lot verification
74
Failure to adjust the QC target value will
Cause inappropriate acceptability criteria to be used for evaluating the QC results
75
When a new lot of calibrator is used, with no change in reagents
There is no change in matrix interaction between the QC material and the reagents
76
provide a reliable indication of calibration status with the new lot of calibrator
QC results
77
If the QC results indicate a bias following use of a new lot of calibrator
the calibration has changed and needs to be corrected to ensure consistent results for patient samples
78
four principal ways to support the QC processes in a laboratory
o To verify consistency of patient results when changing lots of reagent or calibrators for a method (discussed in the previous section)
o To identify inconsistent results using a delta check with a previous result for a patient
o To verify consistency of patient results when an analyte is measured using more than one instrument or method in a health care system
o To verify method performance using results from patient samples in a statistical QC scheme
79
errors that can be identified by comparing a patient’s current test result to a previous result for the same analyte
-useful to identify an interfering substance
delta check
80
require that the relationship between test results from different methods or from multiple locations should be evaluated at least twice a year
• CLIA regulations, section 493.1281
81
important limitation for using patient data to evaluate consistency within a single method, or between different methods for the same analyte
physiologic homogeneity of results
82
Aka “external quality assessment” and “interlaboratory comparison”
Samples are passed on to different laboratories where they will be tested, then the results are compared to the reference value.
Used to verify if the performance of a laboratory is acceptable.
PROFICIENCY TESTING
83
It is the “property of a PT/EQA sample whereby the sample has the same numeric relationship between measurement procedures as observed for a panel of representative clinical patient samples”.
commutability
84
Why are non-commutable PT materials subjected to peer group grading?
There is no reference target value because of matrix-related bias. Hence, they use the second method in comparing results which is to get the mean of all the results. Keep in mind that only laboratories that used the same method and similar technologies can be grouped together.
85
refers to the overall process used to ensure that laboratory results meet the requirements for health care services to patients
QUALITY MANAGEMENT
86
useful indicators of method performance issues
* Frequency of QC alerts
* Frequency of recalibration based on QC alerts
* Number of reagent changes due to QC alerts
* Number of times controls were repeated because of QC alerts
* Frequency of unscheduled maintenance due to QC alerts
* Number of patient samples repeated based on QC alerts
* Frequency that patient samples are repeated based on QC alerts
* Number of patient results corrected
Lab Man
flashcards
Decks in class (9)
# Cards
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Chapter 4 - Principles Of Instrumentation107
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Chapter 5: Clinical Laboratory Automation39
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Chapter 7: Postanalysis58
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Chapter 10: Quality Control86
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Chapter 10: Quality Control (Handout)36
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Chapter 11: Clinical Laboratory Informatics99
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Chapter 12: Financial Management51
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Chapter 12: Documentation14
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Financial Management27
