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Content – Annex. Content. Checklists Glossary of terms References. Annex – Checklists. Checklists. IQC software Administrative capabilities -Easy set-up and modification -Online (real time) connection with LIS -Full sample & IQC traceability -“Accreditation-conform” documentation

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content

Content – Annex

Content
  • Checklists
  • Glossary of terms
  • References

Statistics & graphics for the laboratory

checklists

Annex – Checklists

Checklists
  • IQC software
  • Administrative capabilities
  • -Easy set-up and modification
  • -Online (real time) connection with LIS
  • -Full sample & IQC traceability
  • -“Accreditation-conform” documentation
  • -Up-to-date data safety
  • “IQC”-capabilities
  • -Transparent & efficient data presentation
  • -Great variety of rules
  • -Rule selection logic
  • -Automatic release
  • -Automatic “flags” and remedial action
  • (but with open decision logic)
  • IQC-sample
  • Nature
    • Correspond with patient sample
    • Compatible with the test
  • Concentration: medically relevant
    • Number of levels
  • Stability (liquid versus lyophilized)
  • Lyophilized
    • Variation in fill content
    • Accuracy of reconstitution
  • Target mean
    • Sufficient digits
    • System specific
    • Uncertainty
  • Target SD/CV
    • Representative for system
    • Uncertainty

Statistics & graphics for the laboratory

checklists3

Annex – Checklists

Checklists
  • “Stable” imprecision
  • Instrument stability (general system robustness), e.g.:
  • Pipetting
  • Temperature
  • Photometer (wavelength/intensity/sensor)
  • Test stability & reproducibility (individual test robustness)
  • Total/within-day CV (CVa,tot/CVa,w ratio)
  • Calibration tolerance (within/between lot), -function
  • Reagent (within/between lot)
  • Test robustness
  • Note: Ideally, a GUM-type variance analysis of all elements should be available.
  •  Decide about approaching the variation by IQC and/or quality assurance

Statistics & graphics for the laboratory

checklists4

Annex – Checklists

Checklists
  • IQC-measurement-frequency and location
  • Minimum: 2 samples per run
  • Desirable: ~1-2% of patient samples
    • -Make a cost/benefit calculation
  • Frequency should be related to test stability: requires knowledge of instrument and test
  • Consider “dummy” measurements before 1st IQC
  • Frequency may depend on the control rule
  • Block: Maximizes chance of assignable cause of variability between subgroups
  • Continuous: Maximizes chance of assignable cause of variability within subgroups
  • Basic statistics
  • Calculations
  • Mean
  • SD
  • CV
  • Gaussian (normal) distribution
  • Graphic of the usual & the cumulated distribution
  • Probabilities within certain distances (s) of the mean
  • Probabilities outside certain distances (s) of the mean
  • 1-sided and 2-sided probabilities
  • Important values for s
  • Convention on “rare events”
  • Possibility of wrong decisions
  • The 1st IQC principle: monitoring the outsides
  • Metrology, knowledge of
  • The total error concept (TE, SE, RE)
  • Concept of maximum allowable total error (TEa) (process specifications)
  • Critical error

Statistics & graphics for the laboratory

checklists5

Annex – Checklists

Checklists
  • TEa
  • Apply TEa values from the following hierarchy
  • • 1. Clinical models (e.g., cholesterol; glucose)
  • • 2. Biological variation (obtain the database)
    • -Bottom-line values
  • No numbers from 1-2: 3. Expert models
  • No numbers from 1-3: 4. Regulation
  • No numbers from 1-4: 5. Better state-of-the-art
  • Note: Critically review the proposed numbers.
  • Rule selection
  • Statistical basis: A rule is chosen based on Pfr and Ped. SD-limits are taken from stable performance.
  • TEa basis: From a specification for TEa, critical error values can be calculated.
  • From the critical error values, adequate IQC rules can be selected, naturally, on statistical basis.
  • Selection tools: power functions, OPSpecs, the TEa/CVa,tot ratio; the IQC decision tool
  • Power of control rules
  • Ped should be 90%
  • Realistic errors to be detected by IQC are
    • D SE = >2
    • D RE = >3 • REstable
  • Ped AND Pfr increase with
    • lower s-limits (2s > 3s)
    • n (note, some rules are connected to the number of materials: multiples of 2, 3 with 2 or 3 materials)
  • Generally, do not consider rules with Pfr >1%
  • Ped increases by combination of rules
  • Ped of mean and variance rules > than single or combined rules
  • Ped for SE > RE
  • Pfr at non-zero can be minimized by movement of the power curve
  • The power curve should have a good steepness

Statistics & graphics for the laboratory

checklists6

Annex – Checklists

Checklists
  • Input elements for a successful IQC policy
  • The guiding rule (regulation)
  • Knowledge
    • Basic statistics
    • Power functions
    • TE error concept (metrology)
    • TEa (critical errors, specifications)
    • Selection of TEa values (and problems)
  • IQC Software
    • Additional: rule selection tools
  • Adequate samples
  • Adequate frequency (and location) policy
    • Cost/benefit calculations
  • Instrument stability data
  • Test stability and reproducibility data
  • Integrated rule selection (TEa; statistics; costs)
    • Release of patient data
    • Process control
  • Remedial actions policy
    • Release of patient data
    • Process control
  • Integration of IQC in the overall quality management
  • Dedicated personnel

Review your current practice

Which~

  • Tests
    • Stable performance~
    • Known?
    • Compared to manufacturer claim/Peers?
    • Compared to medical requirements?
  • Materials~
    • Sort and concentration
    • Targets (mean & CV)
    • Frequency (run-length)
  • Rules (& software)
  • Remedial actions policy~
    • Responsible for interpretation
    • % of non-billable tests (calibration, IQC, repeat)
  • Remedial actions: success-rate

Statistics & graphics for the laboratory

glossary and abbreviations of terms iqc

Annex – Glossary of terms

Glossary (and abbreviations) of terms – IQC
  • Ped: probability of error detection
  • Pfr: probability of false rejection
  • TEa: total allowable error
  • DSEcrit, critical systematic error: the amount of systematic error that places 5% of results outside TEa
  • DREcrit, critical random error: the amount of random error that places 5% of results outside TEa
  • ARL, average run length: the average number of runs that occur before a run is rejected by the IQC procedure
  • Glossary of terms – IQC rules
  • Control rules with a fixed limit 
  • a) Control rules in the form of Nz•s (N is the number of observations, z•s is a certain number of standard deviations of the Gaussian distribution, commonly used are 2s, 2.5s, or 3s).
  • 13s: refers to a control rule where action is taken when one measurement falls outside the ±3s range around the target value.
  • 22s: refers to the situation where action is taken when two consecutive measurements exceed the same limit, either the +2s or -2s range.
  • b) Range rules
  • R4s: refers to a situation where action is taken when the absolute difference between the highest and the lowest result exceeds 4 • s (Westgard interpretation: one >+2s, the other <-2s).
  • c) Others 
  • 7X(mean): 7 consecutive measurements lie on one side of the target
  • 7t : 7 consecutive measurements show a trend (increasing/decreasing)

Statistics & graphics for the laboratory

glossary of terms iqc rules

Annex – Glossary of terms

Glossary of terms – IQC rules
  • Control rules with variable limit (depending on the number of observations N), however, a fixed probability of false rejections (Pfr): XPfr
  • 10.05: 1 control measurement in a group of N measurements exceeds a limit based on a Pfr of 0.05. The limit widens when N increases (tables are available).
  • X0.05 : The mean of a group of N measurements exceeds a limit based on a Pfr of 0.05 (also called "mean" rules). The limit decreases when N increases (tables are available).
  • R0.05: The range in a group of N measurements exceeds a limit based on a Pfr of 0.05. The limit increases when N increases (tables are available).
  • Chi20.05: The ratio s2obs(N-1)/s2 exceeds the critical chi-square value at a Pfr of 0.05 (sobs is the standard deviation calculated from the control measurements, s is the intrinsic standard deviation) (also called "variance" rules). The limit increases when N increases (tables are available).
  • CS ("CUSUM"): The difference between individual results and the mean is summed up and plotted. Interpretation is either graphical ("V" mask) or with a numerical limit.

Statistics & graphics for the laboratory

references

Annex – References

References
  • Statistical textbooks
  • Basic
  • Miller JC, Miller JN. Statistics for analytical chemistry. 3rd ed. Chichester (UK): Ellis Horwood, 1993.
  • Advanced
  • Sokal RR, Rohlf FJ. Biometry. 3rd ed. New York: W. H. Freeman and Company, 1995.
  • Altman DG. Practical Statistics for medical research. Chapman & Hall, London, 1991.
  • Electronic textbook
  • www.statsoft.com/textbook/stathome.htm
  • http://faculty.vassar.edu/lowry/VassarStats.html
  • Software for laboratory statistics
  • www.cbstat.com
  • www.medcalc.be
  • www.marquis-soft.com
  • IQC-websites
  • www.westgard.com
  • www.marquis-soft.com
  • IQC-software
  • QC-today: www.ilww.com
  • Unity: Bio-Rad
  • EZ Runs: Westgard
  • QC Validator. EZ-rules. Westgard Quality Corporation. www.westgard.com.
  • Useful links
  • Regulation
  • www.iph.fgov.be
  • www.baek.de
  • www.cms.hhs.gov/clia/, and www.phppo.cdc.gov/clia/regs/toc.asp
  • www.cenorm.be
  • www.iso.ch

Statistics & graphics for the laboratory

references10

Annex – References

References
  • IQC-general
  • National Committee for Clinical Laboratory Standards (NCCLS).C24-A2. Statistical quality control for quantitative measurements: Principles and definitions; Approved Guideline – 2nd ed (1999).
  • Westgard JO, Barry PL. Cost-effective quality control. AACC Press, 1995
  • Shewart WA. Economic control of manufactured products. Van Nostrand: 1931.
  • Levey S, Jennings ER. The use of control charts in the clinical laboratory. Am J Clin Pathol 1950;20:1059-66.
  • Westgard JO, Groth T, Aronsson T, Falk H, de Verdier C-H. Performance characteristics of rules for internal quality control: probabilities for false rejection and error detection. Clin Chem 1977;23:1857-67.
  • Hyltoft Petersen P, Ricós C, Stöckl D, Libeer J-C, Baadenhuijsen H, Fraser CG, Thienpont LM. Proposed guidelines for the internal quality control of analytical results in the medical laboratory. Eur J Clin Chem Clin Biochem 1996;34:983-99.
  • Linnet K. Mean and variance rules are more powerful or selective than quality control rules based on individual values. Eur J Clin Chem Clin Biochem 1991;29:417-24.
  • IQC-practice surveys
  • Steindel SJ, Tetrault G. Quality control practices for calcium, cholesterol, digoxin, and hemoglobin. A College of American Pathologists Q-probes study in 505 hospital laboratories. Arch Pathol Lab Med 1998;122:401-8: Recommend 2.5 – 2.7s rule
  • Tetrault GA. QC in the clinical lab: 6 questions for the pathologist. CAP Today 1995 (April):60-1: Recommends 3.5 s rule
  • Steindel SJ. Quality control systems in the clinical laboratory. A survey on implementation in 505 hospital laboratories. Labmedica Int 1999;16:8-12: Recommends 2.5 – 2.7s rule
  • Krishnan S, Webb S, Henderson AR, Cheung CM, Nazir DJ, Richardson H. An overview of quality control practices in Ontario with particular reference to cholesterol analysis. Clin Biochem 1999;32:93-9.

Statistics & graphics for the laboratory

references11

Annex – References

References
  • Quality management
  • ISO 8402: 1994. Quality management and quality assurance - Vocabulary
  • National Committee for Clinical Laboratory Standards (NCCLS). HS1-A (replaces GP26-A). A quality system model for health care; Approved guideline (2002).
  • ISO/DIS 15189.2 Medical laboratories - Particular requirements for quality and competence.
  • Burnett D. Understanding accreditation in laboratory medicine. ACB Venture Publications. London: Association of Clinical Biochemists, 1996.
  • Stewart CE, Koepke JA. Basic quality assurance practices for clinical laboratories. Philadelphia (USA): J. B. Lippincott Company, 1987.
  • Garfield FM. Quality assurance principles for analytical laboratories. AOAC International: 1994.
  • St John A. Critical care testing. Quality assurance. Mannheim: Roche Diagnostics, 2001.
  • Nilsen CL. Managing the analytical laboratory: plain and simple. Buffalo Grove (IL): Interpharm Press, 1996.
  • Metrology
  • ISO VIM. Vocabulaire international des terms fondamentaux et généraux de métrologie.
  • ISO GUM. Guide to the expression of uncertainty in measurement
  • ISO 5725-1. Accuracy (trueness and precision) of measurement methods and results.
  • Stöckl D. Metrology and analysis in laboratory medicine: a criticism from the workbench. Scand J Clin Lab Invest 1996;56:193-7.

Statistics & graphics for the laboratory

references12

Annex – References

References
  • Regulation
  • Praktijkrichtlijn voor het opzetten van een kwaliteitshandboek in erkende klinische laboratoria werkzaam binnen het kader van het RIZIV.
  • Royal Decree from December 3 1999 regarding the authorization of clinical chemical laboratories. Moniteur Belge. December 30, 1999. Implementation document: Praktijkrichtlijn (Practice guideline): www.iph.fgov.be/Clinbiol/NL/index.htm.
  • Guidelines of the German Medical Association (Bundesärztekammer) regarding the quality assurance in medical laboratories (RILIBÄK). Deutsches Ärzteblatt 2001;98, 42:A 2747-59 + 2002;99, 17: A 1187. www.bundesaerztekammer.de/30/-Richtlinien/Richtidx/Labor2002/index.html.
  • QC - THE REGULATIONS. Sharon S. Ehrmeyer, Ph.D. www.westgard.com/guest8.htm.
  • Directive 98/79/EC of the European Parliament and of the Council of 27 October 1998 on in vitro diagnostic medical devices. Official Journal of the European Communities 1998 (Dec 7):L 331/1-L 331/37.
  • CEN prEN ISO 17511 (draft Dec 2000) in vitro diagnostic medical devices - Measurement of quantities in samples of biological origin - Metrological traceability of values assigned to calibrators and control materials (ISO/DIS 17511:2000).
  • CEN prEN 13612 (final draft September 2001) Performance evaluation of in vitro diagnostic medical devices.
  • ISO/DIS 15198 (April 2001). Clinical laboratory medicine - Validation of manufacturer´s recommendations for user quality control.
  • CEN EN 591 (2001) Instructions for use for in vitro diagnostic instruments for professional use.
  • CEN EN 375 (2001) Information supplied by the manufacturer with in vitro diagnostic reagents for professional use.
  • CEN prEN 14136 (draft March 2001) Use of external quality assessment schemes in the assessment of the performance of in vitro diagnostic procedures.
  • ISO/IEC 17025: 1999 - General requirements for the competence of testing and calibration laboratories (former EN 45001).
  • ISO/DIS 15189.2 Medical laboratories – particular requirements for quality and competence
  • ISO/AWI 22869 Clinical laboratory testing -- Guidance on application of ISO 15189.
  • NCCLS EP11-P Uniformity of claims for in vitro diagnostic tests; Proposed guideline (1996).
  • NCCLS EP15-P User demonstration of performance for precision and accuracy; Proposed guideline (1998).

Statistics & graphics for the laboratory

references13

Annex – References

References
  • Dignostic value of tests
  • Büttner J. Diagnostic validity as a theoretical concept and as measurable quantity. Clin Chim Acta 1998;260:131-43.
  • Linnet K. A review on the methodology for assessing diagnostic tests. Clin Chem 1988;34:1379-86.
  • National Committee for Clinical Laboratory Standards. Assessment of clinical accuracy of laboratory tests using receiver operating characteristics (ROC) plots; approved guideline. NCCLS publication GP10-A. Wayne, PA: NCCLS 1995.
  • The Bayes Library of Diagnostic Studies and Reviews. 2nd edition 2002. http://www.ispm.unibe.ch/files/file/261.Bayes_library_handbook.pdf
  • Henderson AR. Assessing test accuracy and its clinical consequences: a primer for receiver operating characteristic curve analysis [Review]. Ann Clin Biochem 1993;30:521-39.
  • Performance specifications
  • Stöckl D, Baadenhuijsen H, Fraser CG, Libeer J-C, Hyltoft Petersen P, Ricós C. Desirable routine analytical goals for quantities assayed in serum. Eur J Clin Chem Clin Biochem 1995;33:157-69.
  • Stöckl D. Desirable Performance criteria for quantitative measurements in medical laboratories based on biological analyte variation - hindrances to reaching some and reasons to surpass some. Clin Chem 1993;39:913-4.
  • www.westgard.com
  • Strategies to set global analytical quality specifications in laboratory medicine. Consensus Statement, Stockholm 1999. Scand J Clin Lab Invest 1999;59:585.
  • Hyltoft Petersen, P. Quality specifications based on analysis of effects of performance on clinical decision making. Scand J Clin Lab Invest 1999;59:517-22.
  • ISO 15196/CD Identification and determination of analytical and clinical performance goals for laboratory methodologies

Statistics & graphics for the laboratory

slide14

Annex

  • STT Consulting
  • Dietmar Stöckl, PhD
  • Abraham Hansstraat 11
  • B-9667 Horebeke, Belgium
  • e-mail: [email protected]
  • Tel + FAX: +32/5549 8671

Statistics & graphics for the laboratory

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