Basics of laboratory internal quality control, Ola Elgaddar, 2012
Basics of laboratory quality control Ola H. Elgaddar MBChB, MSc, MD, CPHQ Lecturer of Chemical Pathology Medical Research Institute Alexandria University Ola.firstname.lastname@example.org
Total Quality Management (TQM) - A continuous approach that seeks to improve quality and performance which will meet or exceed customer expectations. - This can be achieved by integrating all quality-related functions and processes throughout the organization. - TQM requires the involvement of everyone; management, workforce, suppliers, and customers (feedback) - Divided into four sequential categories: plan, do, check, and act
In a medical lab, we have threemain stages that need control:1) Pre-analytical2) Analytical3) Post-analyticalAll of them should be under tight control
1) Pre-analytical:• Patient & specimen identification• Patient preparation• Specimen collection, transport and handling• Monitoring personnel
IQC is used, on daily basis, in the decision toaccept or reject results of patients samplesand enables the lab to describe and monitorthe quality of its work.EQA permits a comparison of quality betweenlaboratories and thus describes the “state ofthe art ” for that area of laboratory workencompassed by the EQA program .It is used to confirm results of IQC
3) Post-analytical:• Transcriptional errors• Unclear report format or information
IQC procedures• A stable control material which mimics patient’s sample is analyzed (day to day)• Individual measurements are plotted on a control chart (Levey Jennings charts)• Evaluation whether measurement is “in control” (Westgard multi-rules)
Control materialIFCC defines control material as a solutionanalyzed solely for Q.C. purpose and not forcalibrationCriteria to be considered:• 1. Matrix• 2. Reconstitution• 3. Stability• 4. Assayed or un assayed• 5. Appropriate analyte level
1) Matrix:-BASE from which the control material isprepared.-Ideally the same matrix as specimen so thatthey behave like a specimen.- Controls available are HUMAN BASED orBOVINE BASED
2) Reconstitution:• Liquid / lyophilized (Liquid controls better)• Reconstitution material• Quantity of solvent (volume?)• Mixing• Waiting (when to use the reconstituted control)• Vial to vial variation(Standardization of these factors necessary)
3) Stability:• Expiry date and stability after reconstitution should be considered• Desirable is one year supply of the same lot, so that the lab can have its own QC range for a longer period of time.
4) Assayed / Un-assayed QC:• Assayed QC material are the usually used type in our labs• They have manufacturer values for each instrument / method• Those values should be considered as guidelines only till each lab establish its own QC range• Minimum period of time for a lab to establish its own range is 20 days• Ideally, a new QC lot should be run, hand in hand with the old lot, its values are established before it is run routinely.
5) Appropriate analyte level• The used QC material should be covering the measured range of the analyte, both in its normal and pathological range.• It is preferable to have a control value near the medical decision level.• Ideally, there are two levels of QC material used in Chemistry analysis and three levels for hormones and tumor markers.
Plotting QC result on Levey Jennings control chart• Mean and SD of QC material (manufacturer or each lab’s values)• Y-axis: control value Vs X-axis: time of run• Most autoanalyzers plot the charts, otherwise they should be drawn manually• A chart is plotted for each control level
Evaluating QC results using Westgard rules• Detects whether results are “in control” or not.• Detects the type of laboratory error
• Random error, RE, or imprecision is described as an error that can be either positive or negative, whose direction and exact magnitude cannot be predicted, where the distribution of results when replicate measurements are made on a single specimen.• Usually, due to error in pippetting
• Systematic error, SE, or inaccuracy is an error that is always in one direction, displacing the mean of the distribution from its original value.• In contrast to random errors, systematic errors are in one direction and cause all the test results to be either high or low.• Either constant or proportionate• Usually, due to error in calibration