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Quality Assurance in Hematology Dr.Mohamed Iqbal Musani, MD. Introduction. QA is the sum of all those activities in which the laboratory is engaged to ensure that information generated by laboratory is correct.

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introduction
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 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.
introduction cont
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 testing ( eg : preventive maintenance and calibration of instruments, testing of media, orientation and training of personnel )

introduction cont4
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 )

qa in haematology laboratory
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 )

slide6
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

internal quality control iqc
Internal Quality Control ( IQC )
  • based on monitoring the haematology tests procedures that are performed in the lab
  • includes measurements on CONTROLS & 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
external quality control eqc
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 with results of other labs.
control materials
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
statistics of qc
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

analysis of data
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
slide12
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
slide13
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
internal qc
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
external qc
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 )
slide18
A deviation index ( score ) =

actual results – weighted median / mean for test

weighted SD

Interpretation :

0.5 – excellent

0.5-1.0 – satisfactory

1.0- 2.0 – acceptable

> 2.0 – defect requiring attention

slide19
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 )

references
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