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Quality Assurance in Haematology

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1 Quality Assurance in Haematology

2 Introduction QA is the sum of all those activities in which the laboratory is engaged to ensure that information generated by laboratory is correct. QA is not restricted to the development and retention of quality control charts but rather includes all aspects of laboratory activities that affects the results produced, from the choice of methods, to the education of personnel, to the handling of specimens and reporting results. The real purpose of QA activities is to determine how correct or incorrect the results emanating from the lab are, and to allow those managing the lab to determine whether or not the lab is fulfilling its functions satisfactorily.

3 Introduction – cont’ 3 major activities of QA :
1 ) Preventive – those activities that are done prior to the examination of the specimen or sample and that are intended to establish systems conducive to accuracy in analytical testing ( eg : preventive maintenance and calibration of instruments, testing of media, orientation and training of personnel )

4 Introduction – cont’ 2 ) Assessment – those activities that are done during testing to determine whether the test systems are performing correctly ( eg : the use of standard and controls, maintenance of control charts ) 3 ) Corrective – those activities that are done, when error is detected, to correct the system ( eg : equipment troubleshooting, recalibration of instruments )

5 QA in Haematology Laboratory
QA in haematology lab is intended to ensure the reliability of the lab tests. The objective is to achieve precision and accuracy 4 components of QA programme : 1 ) Internal Quality Control ( IQC ) 2 ) External Quality Control ( EQC ) 3 ) Standardization 4 ) Proficiency surveillance

6 Accuracy - the closeness of the estimated value to the true mean - can be checked by the use of reference materials which have been assayed by independent methods of known precision Precision - reproducibility of a results, whether accurate or inaccurate within a define frame time ( eg: within the same day, from week to week etc ) - can be controlled by replicate tests, check tests on previously measured specimens and statistical evaluation of results

7 Internal Quality Control ( IQC )
based on monitoring the haematology tests procedures that are performed in the lab includes measurements on specially prepared materials, and repeated measurements on routine specimens, statistical analysis and day by day data obtained from the tests which have been routinely carried out is intended to ensure that there is continual evaluation of the reliability of the work of the lab and that control is exercised over the release of the results it is primarily a check of precision but not necessarily accuracy

8 External Quality Control ( EQC )
is the objective evaluation by an outside agency of the performance by a number of laboratories on material which is supplied specially for the purpose is usually organized on a national or regional basis analysis of performance is retrospective the objective is to achieve comparability, not necessarily accuracy unless the specimens have been assayed by reference lab, using methods of known precision, alongside a reference preparation of known value

9 Standardization Refers to both materials and methods
A material standard or reference preparation is used to calibrate analytic instruments and to assign a quantitative value to calibrators A reference method is an exactly defined technique which provides sufficiently accurate and precise data for it to be used to assess the validity of other methods International reference preparations are not freely available for routine use but are intended to act as standards for assigning values to commercial ( or lab produced ) ‘secondary standard’ or calibrators

10 Proficiency surveillance
Implies critical supervision of all aspects of laboratory tests ( collection, labelling, delivery, storage of specimens before the tests are preformed and of reading and reporting of results ) Also includes maintenance and control of equipment and apparatus It is necessary for correct interpretation of test results, for the lab to establish normal reference values that are valid for their test methods and their local population

11 Control materials Specially prepared
It may be anticoagulated WB, preserved pooled red cells, plasma or serum It can be used to check for accuracy if the value has been reliably determined ( eg : reference centre ) Should have controls of high, normal and low values At least 1 control specimen should be used for every batch If large specimens, use 1 control for every 20 specimens The same material is used for EQC or also as calibrator

12 A reference standard is a substance ( eg: Hb std ) that has been characterized by chemical or physical means and has been specific values. International reference standard are manufactures by or on behalf an international organization (eg : WHO and International Council for Standardization in Haematology) A reference material is a substance ( eg : plasma ) or device ( eg : reference beads ) that conform to national ar international reference std. This material is used to ensure accuracy of the test procedure A calibrator is a substance or device that conforms to a reference std or specification. It is used to calibrate an apparatus or to adjust a measurement to obtain accurate results

13 Statistics of QC Mean ( x ) the total score of all the measurements divided by the number of measurements Standard deviation ( SD ) – variation in measurement obtained in lab tests formula: SD = Σ ( x – x )2 n – 1 n : number of measurement Coefficient of variation ( CV ) – relation of SD to the actual measurement formula : CV = SD X 100% x

14 Analysis of data Standard deviation of control specimens
if value assigned to a specimen a number of times, dispersion of results around the mean will indicate the error of reproducibility 95% of results on the same specimen should be within ± 2 SD and 99.7% within ± 3 SD by chance, 1 in 20 of measurement might expected to fall outside 2 SD and only 1 in 333 outside 3 SD If measurement more widely dispersed, this indicates an error in the test

15 Control Charts originally described by Shewhart, 1st applied in clinical chemistry by Levey and Jennings Samples of the control specimen are included in every batch of patients’ specimens and the results checked on a control chart To check precision, it is not necessary to know the exact value of the control specimen Value has been determined reliably by a reference method, the same material can be used to check accuracy or to calibrate an instrument If possible, controls with high, low and normal values should be used Advisable to use at least one control sample per batch even if the batch is very small The results obtained with the control samples can be plotted on a chart

16 Cumulative Sum Method ( CUSUM )
is the running total of the difference bet each measurement and the established mean of the control tests It provides another way to display the data obtained in the precision test More sensitive than control chart – faulty technique or instrument Useful for detecting a change in performance d/t drift ( a consistent error in one direction ) or a slight progressive drift away from the original mean The size of change that the test is design to detect can be varied for individual test, clinical significance

17 Duplicate Tests On Patient’s specimens
provides another way of checking the precision of routine work Test 10 consecutive specimens in duplicate under careful conditions Calculate the differences between the pairs of results and derive the SD Subsequent duplicate tests should not differ from each other by more than 2 SD This methods will detect random errors but it is not sensitive to gradual drift nor will it detect incorrect calibration Impractical for routine blood counts in a busy lab A few consecutive specimens in a batch should be tested from time to time as a rough check

18 Use Of Normal Haematological Data For QC
in healthy individuals the blood count remains virtually constant day by day It is possible to use observations on healthy individuals for quality control I routine lab Analyze 5-10 healthy subjects at intervals and calculating mean and SD for MCV, MCH and MCHC On each occasion the mean should not vary by more than 2 SD and the SDs should remains constant A significant difference in mean indicates a constant error eg : incorrect calibration A random error will result in an increase in SD although the mean may be unaffected

19 Use Of Patient Data For QC
to start this programme it is 1st necessary to assay samples from at least patients in an automated blood counter and to establish the means of MCV, MCH and MCHC Analyse the results in successive batches of 20 specimens By plotting this results on graph, any drift from 3 indices can be readily recognized and used to identify instruments faults This method appears to be as accurate and precise as the of preserved blood controls and is especially sensitive to changes in RBC

20 Internal QC Intended to monitor various aspects of test performance which performed in the lab Measurement on specially prepared materials, repeated measurements on routine specimens as well as statistical analysis, day by day, of data obtained from the routine tests which have been carried out in the lab Measures provide a way to achieve precision



23 External QC The major purpose – to achieve harmonization concordance between labs The principle is that the same material is sent from a national or regional centre to a large number of laboratories All the labs send the results back to the centre where they are analysed and interpreted by one of several procedures From the results returned from the participants, the median or mean and SD are calculated An individual lab can then compare its performance in the survey with that of other labs and with its own previous performance ( using deviation index )

24 > 2.0 – defect requiring attention
A deviation index ( score ) = actual results – weighted median / mean for test weighted SD Interpretation : 0.5 – excellent – satisfactory – acceptable > 2.0 – defect requiring attention

25 Assigned values values are assigned to the test materials by expert lab who also establish the SD of the method under optimal condition To ensure that results are clinically reliable, they should be within a certain percentage of the assigned value

26 Organizations – A ) National External Quality Assurance Programme ( NEQAP ) Pusat Darah Negara B ) Royal Collage of Pathologists of Australia ( RCPA ) C ) International EQA Scheme for Haematology ( IEQAS )





31 References Good Laboratory and Clinical Practices – Techniques For Quality Assurance Professional, P A Carson and N J Dent, 1990 Quality Assurance Practices for Health Laboratories, Stanley L. Inhorn, 1978 Royal Postgraduate Medical School University of London, Dr. S. M. Lewis

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