Quality control in histopathology laboratory
- 1. Quality Control in Clinical Chemistry/Immunoassays
- 2. Quality Assurance • Quality assurance (aka QA) – refers to planned and systematic processes that provide confidence of a product's or service's effectiveness. – It makes ‘quality’ a main goal of a production. – From the lab perspective, it is all of the procedures, actions and activities that take place to be sure the results given to the physician are accurate
- 3. The Quality Assurance Cycle •Data and Lab Management •Safety •Customer Service Patient/Client Prep Sample Collection Sample Receipt and Accessioning Sample Transport Quality Control Record Keeping Reporting Personnel Competency Test Evaluations Testing
- 4. Quality Assurance & Quality Control • Quality Control (QC) – A procedure or set of procedures intended to ensure that a manufactured product or performed service adheres to a defined set of quality criteria or meets the requirements of the client or customer. – In the laboratory that means ....…
- 5. Cont…… • At the very basic level in the laboratory, Quality Control - QC refers to the measures that must be included during each assay run to verify that the test system is working properly. Monitors analytical process to allow detection of errors. – This requires the routine gathering & processing of data obtained by testing controls along with patient samples. – The processing of the data very often requires use of statistical procedures.
- 6. Cont…… • Also called internal quality control • It checks primarily the precision (repeatability or reproducibility) of the method.
- 7. External Quality Control (EQC). • It includes all QC methods which are performed periodically(i.e. every month, every two months, twice a year) by the laboratory personnel with the contribution of an external center (referral laboratory, scientific associations, diagnostic industry etc.). • It checks primarily the accuracy of the laboratory’s analytical methods. • However, there are certain EQC schemes that check both the accuracy and the precision.
- 8. Cont… • Other terms for external quality control are: interlaboratory comparisons, proficiency testing (PT) and external quality assessments schemes (EQAS).
- 9. Proficiency testing • Besides QC, Labs are required to participate in proficiency testing program • It is to validate particular measurement method • Specimens have a known concentration of analyte but not known to the participating labs • The sample should always be treated/handled like the patient sample
- 10. True Value – True value – an ideal concept, which cannot be achieved – Accepted True value – The value approximating the ‘True Value’; the difference between the two values is negligible. – Error is the discrepancy between the result obtained in the testing process and its ‘True Value’ / ‘Accepted True Value’
- 11. Error • Sources of Error – Reagents – Standards – Technique – Environment – Specimen collection, handling etc.
- 12. Types of error • Classified as either – Pre analytical – Analytical – Post analytical OR – Systematic or Random
- 13. Pre-Analytical error • Includes clerical error, wrong patient, wrong specimen drawn, specimen mis-handled, etc. • Through Quality Assurance measures, the laboratory tries to maintain control over these factors – Well trained phlebotomy staff – Use of easy patient & specimen identification methods, such as bar code identification. – Willingness to be information resource and / or trainers for physicians and floor personnel often involved with specimen collection.
- 14. Analytical error – Analytical error • Random or indeterminate – Hard or impossible to trace, ie fluctuations in elect. temp, effects of light, etc • Systematic or determinant – Have a definite cause, i.e. piece of equipment that fails to function properly, poorly trained personnel, contaminated reagent • Through Quality Control measures, such as always running controls, the laboratory limits these errors.
- 15. Post-Analytical error • Errors that occur after the testing process is complete. – Clerical error. – Delay • Quality Assurance measures must be implemented if problems identified.
- 16. Quality control chart • Mainly the Levey-Jenning’s chart – Require run of quality control samples – Require statistical analysis's- standard deviation – Calculated from the quality control samples in each run for the day
- 17. QC samples – Standard • Highly purified substance, whose exact composition is known. • Non- biological in nature • Uses – Control or patient results can be compared to a standard to determine their concentration – Used to calibrate an instrument so control and patient samples run in the instrument will produce valid results
- 18. QC samples – Controls • Resemble the patient sample – Have same characteristics as patient sample, color viscosity etc. • Come with range of established values • The results of any run / analysis must compare to the ‘range of expected’ results to determine acceptability of the analysis.
- 19. Statistical concepts • When there are data results of the controls, they can be laid out and evaluated. – Measures of Central tendency ( how numerical values can be expressed as a central value ) • Mean - Average value • Median - Middle observation • Mode - Most frequent observation
- 20. Cont…… • An important tool in the statistical analysis is determining: – Standard Deviation (SD)-a measure of the scatter around the arithmetic average (mean) in a Gaussian distribution (Bell curve, or normal frequency distribution) – Normal or Gaussian distribution (N) is the basis of QC theory – Quality Assessment and Quality Control measures must include a means to identify, classify, and limit error.
- 21. Standard Deviation • For a set of data with a normal distribution, a value will fall within a range of: +/- 1 SD 68.2% of the time +/- 2 SD 95.5% of the time +/- 3 SD 99.7% of the time
- 22. Levey-Jennings Chart • A graphical method for displaying control results and evaluating whether a procedure is in-control or out- of-control • Control values are plotted versus time • Lines are drawn from point to point to accent any trends, shifts, or random excursions • Levey-Jennings chart is the most important control chart in laboratory quality control. • It was firstly introduced in 1952 (Levey S. & Jennings E, 1950).
- 23. Levey-Jennings Chart - Record and Evaluate the Control Values 80 85 90 95 100 105 110 115 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Mean Day +1SD +2SD +3SD -1SD -2SD -3SD
- 24. Findings Over Time • Ideally we should have control values clustered about the mean (+/-2 SD) with little variation in the upward or downward direction • Imprecision = large amount of scatter about the mean. Usually caused by errors in technique • Inaccuracy = may see as a trend or a shift, usually caused by change in the testing process • Random error = no pattern. Usually poor technique, malfunctioning equipment
- 27. Statistical Concepts – Shift – when there are 6 consecutive data results on the same side of the mean
- 28. Statistical Concepts – Trend – when there is a consistent increase OR decrease in the data points over a period of 6 days. (A line connecting the dots will cross the mean.)
- 29. When does the Control Value Indicate a Problem? • Consider using Westgard Control Rules • Uses premise that 95.5% of control values should fall within ±2SD • Commonly applied when two levels of control are used
- 30. Westgard Rules • “Multirule Quality Control” • Uses a combination of decision criteria or control rules • Allows determination of whether an analytical run is “in-control” or “out-of-control”
- 31. Westgard Rules (Generally used where 2 levels of control material are analyzed per run) • 12S rule • 13S rule • 22S rule • R4S rule • 41S rule • 10X rule
- 32. Westgard – 12S Rule • “warning rule” • One of two control results falls outside ±2SD • Alerts to possible problems • Not cause for rejecting a run • Must then evaluate the 13S rule
- 33. 12S Rule = A warning to trigger careful inspection of the control data 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Mean Day +1SD +2SD +3SD -1SD -2SD -3SD 12S rule violation
- 34. Westgard – 13S Rule • If either of the two control results falls outside of ±3SD, rule is violated • Run must be rejected
- 35. 13S Rule = Reject the run when a single control measurement exceeds the +3SD or -3SD control limit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Mean Day +1SD +2SD +3SD -1SD -2SD -3SD 13S rule violation
- 36. Westgard – 22S Rule • 2 consecutive control values for the same level fall outside of ±2SD in the same direction, or • Both controls in the same run exceed ±2SD • Patient results cannot be reported • Requires corrective action
- 37. 22S Rule = Reject the run when 2 consecutive control measurements exceed the same +2SD or -2SD control limit 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Mean Day +1SD +2SD +3SD -1SD -2SD -3SD 22S rule violation
- 38. R4s. The distance of two successive control •values, is over 4s. It is a criterion •sensitive to random errors. The results •should be blocked and not reported to the •patients. (Normally this criterion is used •with two different control levels/across •runs – when used with one level, as in this •example, is applied for two consecutive •runs).
- 39. 41s. Four successive control values lie •between μ+1s and μ+3s or between μ-1s •and μ-3s. It defines a systematic error. The •results should be blocked and not reported •to the patients.