B - CHAPTER IV: QUALITY CONTROL IN CLINICAL CHEMISTRY Flashcards
1
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– a degree to which a set of inherent characteristics fulfills requirements (ISO 9001:2008)
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QUALITY
2
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- part of quality management focused on fulfilling quality requirements (ISO 9000:2000)
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QUALITY CONTROL
3
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• System of assuring the quality of total laboratory performance
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QUALITY CONTROL
4
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• Involves the periodic systematic surveillance of people, tools, methods and reagents
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QUALITY CONTROL
5
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– part of quality management focused on providing confidence that the quality requirements will be fulfilled (ISO 9000:2000)
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QUALITY ASSURANCE
6
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- Set of activities or plan that aims to maintain the highest degree of excellence for the diagnosis & treatment of disease and maintenance of health
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QUALITY ASSURANCE PROGRAM
7
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AREAS of QUALITY CONTROL:
- All [?] are involved.
- The laboratory’s relation to other [?]
- Laboratory [?] should be collected in a manual to be revised at least once a year or when procedures are changed.
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patients, laboratory personnel, laboratory equipment, and laboratory tests
hospital departments
policies and procedures
8
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SYSTEM CONCEPTS of QUALITY CONTROL:
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9
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– establishes norms that must be met
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- Quality Control Surveillance System (QCCS)
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– established to offer education of why errors occur; provide a program to remedy defects
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- Q.C. Corrective System
11
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– established to prove that corrective measures have produced favorable results.
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- Objective Q.C. Parameters
12
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PROCEDURES in QUALITY ASSURANCE PROGRAM
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13
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A. CONTROL of PRE-ANALYTICAL VARIABLES FACTORS:
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14
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B. CONTROL OF ANALYTICAL VARIABLES MAIN FACTORS:
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- Choice of analytical methodology
- Calibration procedures
- Proper documentation of analytical variables
- Proper labeling & use of reagents
- Preventive maintenance of analytical instruments
- Periodic calibration of pipetting devices
- Periodic checking of °T of refrigerator & heating units
- Periodic checking of procedure manuals
- Monitoring of technical competence
- Inventory of control materials
- Control assurance that safety measures are operational
15
Q
C. CONTROL of POST-ANALYTICAL VARIABLES FACTORS:
A
- Verification of calculations of the final results
- Check test results for possible transcription errors
- Results should be easy to read & interpret
- Timeliness of reporting values to patient chart
- Procedures for informing physicians about results that require immediate attention
16
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FACTORS Involved in QUALITY CONTROL
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- STANDARD
- CONTROL MATERIAL
17
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o A substance of known composition
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STANDARD
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o Its value is established by an analytical procedure different from that used in the clinical laboratory
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STANDARD
19
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o A substance which resembles the unknown specimen (patient’s sample)
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CONTROL MATERIAL
20
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o Analyzed daily together with the unknown
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CONTROL MATERIAL
21
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o The values obtained from the assays are used for the computation of the mean and the SD
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CONTROL MATERIAL
22
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Types of Control Material:
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a. Commercial Control Sera
b. Pooled Sera
23
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- are collected daily in the laboratory and pooled for storage in the refrigerator
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Excess non-hemolyzed sera without gross lipemia
24
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- When [?] are collected, centrifuge to remove gross contamination
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1 – 2 liters
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- Filter and divide into aliquots of [?] each
5 mL
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- Stopper and store at
-20°C
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- [?] as needed and mix well before use
Thaw
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ELEMENTS of QUALITY CONTROL:
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– extent to w/c the measurement approximates the true value of the quantity being measured
ACCURACY
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– a.k.a reproducibility; degree to w/c repeated results agree to each other
PRECISION
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– ability of a method to detect a particular substance w/o the interference of some other substances present in the sample
SPECIFICITY
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– ability of a method to detect even the smallest amount of that particular substance tested for
SENSITIVITY
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– ability of a method to maintain its accuracy & precision over an extended period of time 6. PRACTICABILITY – degree to w/c the method is easily repeated
RELIABILITY
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STATISTICAL CONCEPTS in QUALITY CONTROL
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➢ A statement of the extent of random variation in any series of measurement
STANDARD DEVIATION
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➢ A measure of the distribution of values around the mean
STANDARD DEVIATION
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Square of the standard deviation
VARIANCE (s2)
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Used to detect significant differences between groups of data
VARIANCE (s2)
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Determine contributions of various factors to the total variation
VARIANCE (s2)
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Percentile expression of the mean
COEFFICIENT OF VARIATION
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Measure of the relative magnitude of variability
COEFFICIENT OF VARIATION
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QUALITY CONTROL Associated Activities:
1. Assay of control samples
2. Instrument maintenance
3. Statistical Data Analysis
4. Proficiency testing survey
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ASPECTS which the laboratory should avoid or minimize:
1. Analytical Bias
2. Random Analytical Variability
3.ERRORS
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❖ Reported values do not fall along the line of slope when graphed
Analytical Bias
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❖ Reported lab results do not correspond to the correct value
Analytical Bias
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Types of Analytical Bias:
a) Proportional bias
b) Constant bias
c) Combined bias
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Problem on Accuracy (Bias) =
Systematic Error
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Refers to laboratory analyses that are subject to imprecision
Random Analytical Variability
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Random Analytical Variability Types:
A. Proportional variability
B. Constant variability
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Problem on Precision (CV)
Random Error
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– can be systematic or personnel-related
ERRORS
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TYPES OF ERRORS:
A. RANDOM ERRORS
B. SYSTEMATIC ERRORS
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Sources cannot be completely controlled or identified
RANDOM ERRORS
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Increase the extent of variability of results
RANDOM ERRORS
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1. Pipets & volumetric glassware w/ manufacturing variation; electronic & optical variations in instruments (e.g. spectrophotometers)
RANDOM ERROR
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2. Variations in the cuvet
RANDOM ERROR
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3. Variations in timing & °T control
RANDOM ERROR
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4. Variations in light, evaporation & °T on serum sample
RANDOM ERROR
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5. Interferences from other substances in the sample
RANDOM ERROR
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Displace the mean value on one direction (may be up or down), but do NOT affect the overall variability as shown by the SD value
SYSTEMATIC ERRORS
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1. Aging phenomena – decomposition of reagents during storage
SYSTEMATIC ERROR
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2. Personal bias of the analyst
SYSTEMATIC ERROR
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3. Laboratory bias
SYSTEMATIC ERROR
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4. Inter- & intra-individual bias
SYSTEMATIC ERROR
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5. Experimental errors or changes in the methods
SYSTEMATIC ERROR
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- Series of values on the control chart that continue to increase or decrease for at least a period of six (6) consecutive days
TREND
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CAUSES of UPWARD TREND:
o Expired lamps/photocells
o Denatured standard
o Contamination of reagents
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CAUSES of DOWNWARD TREND:
o Standards that are too concentrated
o Contamination of reagent
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- Values that distribute themselves on one side of the mean for at least six (6) consecutive days
SHIFT
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CAUSES of UPWARD SHIFT:
o Partial electrical failure in instrument
o New standard is over-diluted
o Denatured standard that has stabilized
o Improperly prepared reagent
o Inaccurate timer
o Deteriorated indicator
o Dirty glassware
o Overheating in °T-sensitive analysis
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CAUSES of DOWNWARD SHIFT:
o Increased concentration of standard & reagents
o Contaminated reagents
o Inaccurate timer
o Under-heating in analysis
o Contaminated glassware
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DIVISIONS of QUALITY CONTROL
INTRALABORATORY / INTERNAL
INTERLABORATORY / EXTERNAL
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Q.C. procedures performed on a daily basis within individual laboratories
INTRALABORATORY / INTERNAL
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INTRALABORATORY / INTERNAL Monitoring is carried out using:
o Levey – Jennings Chart
o Westgard Multi-rule Chart
o CUSUM Technique
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Performed on a less frequent basis (e.g. 3x a year) to compare performance b/w or among laboratories
INTERLABORATORY / EXTERNAL
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– graphical representations that display the control observation as a function or time
QUALITY CONTROL CHARTS
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Control results are plotted on the Y-axis (ordinate) vs time on the X-axis (abscissa)
LEVEY – JENNINGS CHART
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IN-CONTROL:
All control values are w/in ± 2SD
One outlier in 20 determinations
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OUT-OF-CONTROL:
Presence of two or more outliers
Presence of a Trend
Presence of a Shift
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- a control value that goes beyond ±2SD
Outlier
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Causes of Outlier
o Contamination of a single specimen
o Faulty pipette
o Incorrect dilution of test
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Uses a series of control rules for interpreting data
WESTGARD MULTIRULE CHART
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False rejection is kept low
WESTGARD MULTIRULE CHART
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Error detection is improved
WESTGARD MULTIRULE CHART
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Analyse samples of the control material by the analytical method to be evaluated (at least 20 days)
WESTGARD MULTIRULE CHART
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One control observation exceeds ±2SD Warning
12S
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2 consecutive values exceed ±2SD
22S
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One value exceeds ±3SD
13S
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One value exceeds +2SD & the other value exceeds -2SD
R4S
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4 consecutive values exceed ±1SD
41S
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10 consecutive values fall on one side of the mean
10X
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Hands-on process with the single mantra of “improvement”
SIX SIGMA
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SIX SIGMA Improved:
performance
quality
bottom line
customer satisfaction
employee satisfaction
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The # of defects per million opportunities (DPMO) is measured
SIX SIGMA
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Provides a display of the differences b/w the observed values & the expected mean
CUMULATIVE SUM (CUSUM) CHART
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Obtain the CUSUM by adding the difference (value from the mean) to the CUSUM of the previous differences
CUMULATIVE SUM (CUSUM) CHART
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o Examine the slope of the CUSUM line
CUMULATIVE SUM (CUSUM) CHART
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o A steep slope suggests the presence of SE (Out of Control)
CUMULATIVE SUM (CUSUM) CHART
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– found in clin. Laboratories w/ microcomputer Q.C. programs
o DECISION LIMIT CUSUM
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Laboratory’s observed mean for material A (Y-axis) compared to the observed mean for material B (X-axis)
YOUDEN PLOT / SCATTER DIAGRAM
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Information about the nature of the SE can be obtained when two diff. control materials have been analyzed
YOUDEN PLOT / SCATTER DIAGRAM
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OTHER QUALITY CONTROL TOOLS
1. CHECK SHEET
2. PARETO CHART
3. CAUSE & EFFECT DIAGRAM
4. FLOW CHART
5. HISTOGRAM
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- Presents information in an efficient, graphical format
CHECK SHEET
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- Accomplished with a simple listing of items
CHECK SHEET
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- Used to identify factors that have the greatest cumulative effect on the system
PARETO CHART
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- Ishikawa or Fish bone diagram
CAUSE & EFFECT DIAGRAM
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- Used to associate multiple possible causes with a single effect
CAUSE & EFFECT DIAGRAM
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- Primary branch
CAUSE & EFFECT DIAGRAM
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- Major branches
CAUSE & EFFECT DIAGRAM
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- Minor branches
CAUSE & EFFECT DIAGRAM
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- Pictorial representations of a process
FLOW CHART
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- Used in identifying where errors are likely to be found in the system
FLOW CHART
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- Provides a simple, graphical view of accumulated data, including its dispersion & central tendency
HISTOGRAM
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- Ease of construction
HISTOGRAM
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1. Patient identification
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2. Proper preparation of patient
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3. Specimen collection, separation & processing
118
1. Choice of analytical methodology
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2. Calibration procedures
120
3. Proper documentation of analytical variables
121
4. Proper labeling & use of reagents
