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Transcript
Many lab professionals think Quality
in a Medical Laboratory is ….
• Accurate
• Timely
RESULTS
• Reliable
• Reproducible
INSTITUTE OF BIOCHEMISTRY WELCOMES YOU ALL TO THE
CME
ON
“QUALITY ASSURANCE IN CLINICAL LABORATORY
UP, CLOSE & PERSONAL”
8 rights make Quality in a Medical
Laboratory is ….
•
•
•
•
•
•
•
•
Choosing the Right test
Collecting Right Specimen
After Right patient preparation
Testing by the Right method
Reporting the Right based on
Right Reference intervals at the
Right time and at the
Right Price
Where can you go wrong in a lab ?
Material
Suppliers
X
r
M
Equipment
Tissue
Process or
Techniques
Y
s
M
Result:
 Accuracy
 Precision
 Reliability
 Efficiency
 Confidentiality
Microbial
Contamination
Physical Damage
or Contamination
Environment
Personnel
Information
Patient or Client
(sample sources)
Quality is ….
• A subjective term - for which each person has his / her own
definition
• Technically Quality can have two meanings
• A product or service that fulfills the defined and expected
requirement
• stated and implied needs
• A service or product free from defects & deficiencies
Stages of Quality - Hierarchy
QUALITY
MANAGEMENT
QUALITY SYSTEM
QUALITY ASSURANCE
QUALITY CONTROL
WHO definition of QA & QC is ….
• QA - Includes Internal QC, External QA, pre-analytic
phase, test standardization, post-analytic phase,
management, and organization (WHO, 1992)
• QC - Internal quality control (IQC) – set of procedures
for continuously assessing laboratory work and the
emergent results; immediate effect, should actually
control release of results (WHO, 1981)
Quality Assurance & Quality
Control - difference is ….
• QA is for correction & prevention of errors or defects
in the entire lab
• QC is detection of errors and defects in testing process
Purpose of Internal & External QC
Internal QC
• For CONTINUOUS & IMMEDIATE (DAILY) monitoring
of the laboratory work and the emergent results in order to
decide whether the results are reliable enough to be released
to physicians (WHO, 1981)
• Measures Precision & Repeatability of the systems &
methods in use in the lab.
• Illusion of ‘short term accuracy’ of the lab results.
• Do not detect the accuracy or trueness of patient results over a
‘longer term’
Purpose of Internal & External QC
External QC
• For PERIODIC AND RETROSPECTIVE monitoring of lab
results by an independent external agency to indicate to the
laboratory and its staff the accuracy or bias in their systems &
methods
• Lab can know its shortcomings and change their Internal Quality
Assurance procedures.
Why EQAS is necessary?
• Serves as an educational tool and help to monitor & improve the
performance of the lab
• Measures the accuracy or bias of its results and stability of
methods – Over a longer period of time in terms of years
• Mandatory requirement for applicant & accredited labs
• Non participation or repeated failures in an EQAS or PT
programme may result in temporary suspension or cancellation of
accreditation for those non EQAS tests
• Gives the laboratories, both the management & technical staff,
added confidence in their patient test results
WHAT DOES IT IDENTIFY ?
• Identifies systematic kit & reagent problems, water quality
problems, analyte calibration stability and status, equipment
performance
•Indicator of where to direct improvement efforts
•Identifies training needs of lab personnel
• Benchmarks the lab’s performance against others
• Early Warnings System for Problems
HOW SHOULD IT BE USED ?
• Should only be used for motivating staff & not to
punish them
• Inaccurate lab results are not due to technicians
• But due to failure of lab systems
HOW SHOULD IT BE USED ?
•EQAS / PT samples should be treated exactly as the patient
samples Only then the correct situation in the lab can be found
fixing the problem becomes easy
Never
• Run the calibration on the day of reporting EQAS sample if it is
not a scheduled /required calibration
• Repeat the EQAS samples where as the patient samples are tested
only once and give the mean of multiple runs
• Ask a specific analyst run the EQAS / PT sample
REMEMBER EQAS ….
• SUPPLEMENTS Internal Quality Control
• NEVER a SUBSTITUTE for Internal QC
• Both measure 2 different aspects of quality
INTERPRETATION OF EQAS REPORTS
1.VIS – Variance Index Score
2. SDI –Standard Deviation Index
3. Z-Score – Classical & Robust
Variance Index Score
• First proposed by the United Kingdom National Quality Control
Scheme (UKNEQUAS)
• CCV (Chosen Co-efficient of Variation) & DV (Designated Value)
used to calculate VIS
• CCV is just the Allowable Limit of Error for an analyte (TEa) Sum of both imprecision and bias
• Set & recommended by WHO after studying the performance of
many Indian labs
CCV of some common Analytes
Glucose
Urea
Creatinine
7.5
10
10
Sodium
Potassium
Chloride
2.3
5.0
6.0
CK
T.Bilirubin
T.Protein
7.3
19.2
7.5
AST
ALT
ALP
12.5
17.3
15.5
Albumin
Calcium
Uric acid
Cholesterol
7.5
6.0
7.7
7.5
Amylase
LDH
Phosphorus
Bicarbonate
15.5
15.5
7.8
9.0
TGL
14
HDL- C
7.6
HDL
7.6
Iron
15
Calculation of VIS
Designated Value [DV] = 120 mg %
Participant's result
= 95 mg%
% Variation [%V]
= Participant's Result - Designated value
--------------------------------------X 100
Designated value
120-95
120
X 100 =
=
Variance
Index
=
%V
X
CCV
VIS = 277
25 X 100
120
20.8
100 = 20.8
X
7.5
100 =
277
Calculation of VIS
How to read the EQAS results ?
• Check the VIS & OMVIS values for each parameter every month
• Check if your value is close to DV
• Closer it is lower will be your VIS & better is your lab’s accuracy
• Remember If your VIS is < 50 it is regarded and given as zero score
•Even if >400, it is still given as 400 only
Interpretation of VIS
VIS
Performance
< 100
Very good
100 -150 good
150 -200 satisfactory room for improvement
> 200
Not acceptable
• If VIS of >200 on two or more occasions for the same analyte,
them check your standardization procedures & calibration
• Indicates an accuracy problem (systematic error / bias )
Interpretation of VIS
Check the monthly OMVIS.(Overall Mean VIS) cumulative
performance over a period
OMVIS
Performance
< 100
Very good - your result are very close to DV
150-200 Need to take care of those parameters for which
the reported values are very different from the DV for that particular
method
> 250
You are probably reporting many wrong results &
you should take urgent steps to locate the problem and correct them
• The ‘Method Mean' - Mean obtained from results of all
Calculation
VIS
– Method
Mean
participating labs
followingofthe
same
method including
results of
outliers
• The ‘Designated Value’ is the value obtained after excluding
results, from labs with same method, which are > 3SD of Method
Mean and recalculating the mean after eliminating the outliers - Mean
of ‘inliers only’
The 'Reference Mean' - Mean obtained at the organizing lab after
exposing the QC samples to ambient temperature (25-35 C) for a
period of 7- days (transport time) and analysing them on five
different days
The reference mean is shown against the method by which it was
analysed in the organizing lab
Mean value obtained at
the Reference Lab (CMC)
after exposing 5 vials to
ambient Temp. for 9
days and analyzing them
on 5 diff. days
Mean value obtained at the
Reference Lab (CMC) after
exposing 5 vials to ambient
Temp. for 9 days and analyzing
them on 5 diff. days
Mean value of results from
of all participating labs with
same method
Value given (DV) is the mean of all
participating labs for that method after
excluding results from labs outside 3SD
of the Mean Value (of the participating
labs with the same method)
STANDARD DEVIATION INDEX
• Another Statistical tool – assigned to the lab by
the EQAS / PT provider on the performance of
the lab for each analyte in a EQAS cycle
• A measure of relative inaccuracy / relative bias
What is normal or Gaussian
distribution ?
Out of 100 results
• 68.2% of values fall
within ± 1SD
• 95.5% of values fall
within ± 2SD
• 99.7% of values fall
within ± 3SD
IS KNOWING SDI USEFUL ?
• Yes - A measure of the result around a mean among a
group of values
• Since 95 % of all results in a normal population fall
within ± 2 SDs of the mean, +2 SD is considered an
acceptable laboratory value
• Expressed in the units being measured
IS KNOWING SDI USEFUL ?
• The number of Standard Deviations that your lab’s mean differs
from the Peer Group Mean
• . Difference is converted into SD units (SDI)
•The SDI indicates how large / small the difference is between
your result and target value
•Simply said
‘Difference between your result and group mean in
terms of the number of standard deviations from
the overall mean’
IS KNOWING SDI USEFUL ?
• Actual magnitude of the difference in the units of the
test may look too small or too large
• To figure the actual size of this inaccuracy / bias in
concentration units, you need to multiply by the actual
SDI by of the group SD.
• For e.g if the group mean is 102 mg/dL for TGL and
group SD is 5 mg/dL and your SDI score is 1.2
• Actual quantitative difference is 1.2 x 5 = 6 mg/dL
IS KNOWING SDI USEFUL ?
• Any SDI of 2.0 or greater in a EQAS cycle for any
analyte deserves special concern – indicates some for of
systematic error
• Any test whose average SDI is 1.0 or greater deserves
some special attention because your method shows a
systematic difference from the group.
• Likely to lead to unacceptable results in future
• SDI up to 1.0 – your performance is satisfactory – your
result is with 1 SD of the group – you are with in the
68.7 % of lab’s result whose values are close to mean
IS KNOWING SDI USEFUL ?
if you observe SDIs such as -0.4, 0.2, -0.5 - 0.5, - 0.5 and -1.0 (all
negative) for an analyte in successive
cycles, your method is generally
running on the low side and is
negatively biased, on average, by +0.6
SDI
You are reporting precise pateint
values but lower than the true value
by 0.6 SD ()
So better
calibrate your instrument and analyte
or requires instrument maintenance
Z-Score
• Classical Z Score – same as SDI
• Can be used for internal quality control also
Z-Score
• Robust Z score statistic is used when the distribution of results
of participating labs is not Gaussian (not ‘normally’ distributed)
and there are varied results / outliers
• Both accuracy and precision (repeatability as well as
reproducibility) are assessed in terms of robust Z score - both
within and between labs Z score (ZB & ZW)
•The participant labs are asked to analyse the same sample
TWICE and submit both results to the EQAS provider
Z-Score
Z-Score
Robust Z score =
Normalised Lab’s result- Median result of all labs )
Normalized IQR ( Inter Quartile Range)
It is calculated based on the “median” value (central value) and the
‘interquartile range’
All results from participating labs are arranged in an ascending manner (lowest
to highest) the central value is taken as the median
The 25th and 75th percentile values are calculated The ‘interquartile range is the
difference between the 75th & 25th percentile
The 25th quartile (Q1) is the value below which a quarter of the results lie.
Similarly, the 75th quartile (Q3) is the value above which a quarter of the results
lie.
IQR = Q3 - Q1
Normalized inter quartile range (NIQR): NIQR = IQR x 0.7413 (a
constant)
Z-Score
The between laboratory Z-score (ZB) =
(S - median ) / (IQR x 0.7413)
S = (A + B)/[square root of (2)] = standardised sum of
the two results for a laboratory (where A and B are
results of two samples of the same test).
Within laboratory Z-score (ZW) =
(D- median / (IQR X 0.7413)
D = (A - B)/[square root of (2)] = standardized
difference between the two results for a laboratory While
testing two specimens in an EQAS / PT programme by
a lab performance both ZW and ZB should be
considered simultaneously for assessing the performance
Z-Score
Interpretation of Robust Z-scores:
Z score less than 2 - Satisfactory
Z score 2 but less than 3 - Questionable perfromance
Z score more than 3 – Unsatisfactory
Both ZB & ZW should be < 2
Using only one Z-score may misleading
ZW < 2 ZB > 2 = Higher bias i.e low reproducibility
ZB < 2 ZW > 2 = low precision (i.e., low repeatability)
For assessing laboratory's technical competency, both
ZW and ZB value should be low at the same time.
EXERCISES ON INTERPRETATION
OF EQAS REPORTS
Dr.V.K.Ramadesikan
Why Analysis of EQAS reports is important ?
• True benefit of EQAS /PT proficiency testing, lies in
carefully & critically evaluating your results and report
• Proper analysis of EQAS testing results can reveal
problems even before failure in EQAS or even an
adverse patient result
• Potential problems can be recognised by recognising
patterns from graphs
• Review both the present cycle results as well as
performance from previous cycle for the same analyte
• Graphs of Z score or SDI or VIS or % deviation
for trends
• Otherwise trends will be missed
How to recognise problems ?
• Results may consistently be different from the
target peer group mean - All results on one side
of the mean (may be close to mean or at variable
distances from mean) – Systematic Error
• Majority of results are close to the target value
but some show larger deviation s on one side or
both side of mean – Random Error
• Reasons and hence corrective action differs
How to recognise problems ?
• Random error is an error / mistake / inaccuracy that has no set
pattern. Its occurrence cannot be predicted
• Results on an average are close to target mean. Few results show
large deviations on either side of target
• Detected by sudden, undue % deviation /SDI /Z Score – > 3.5
• Indicates lab’s imprecision / poor reproducibility
• Easily identified – values are far beyond the usual – e.g SDI from
1.5 to 4.0 – 6.0
How to recognise problems ?
• Systematic error – set pattern of error / mistake. Its occurrence
can be explained and corrected
• Constant difference between the participant lab’s value and
group mean All results lie on one side of mean
• Indicates lab’s bias or inaccuracy but good precision
• A progressive increase in deviation on the same side – ‘ shift’ or
stabilizes after a gradual increase ‘trends in
Sources of Random Errors
• Random errors are blunders
• Transcription errors – result not correctly transcribed from the
instrument to workbook or PT sheet or from the Workbook to the
system
• Misplaced decimal points e.g serum potassium 58.2 instead of 5.82
• Result was entered in the wrong instrument or method group on the
result form of PT provider.
• Lab might have changed the method or instrument recently but not
updated with PT provider
Sources of Random Errors
• Mislabeling errors, interchanging results of PT specimens,
misplacing specimens in analyser rack, inappropriate reagents and
standards
• Result of some other analyte entered in the PT form of the
provider in the system
• Wrong units. Result in one unit in the instrument but not converted
to unit of EQAS provider e.g ug /mL instead of ng/L , mg/dL
instead of g/L
• Result found on evaluation report from PT provider not matching
with the result on the report form mistake of PT provider
• Calculation errors (conversion from one unit to another)
Sources of Systematic Errors
• Recalibration if not done earlier – esp if a new lot of reagent has
been used or if the open vial stability of the reagent is doubtful
• Instrument maintenance – major part needs servicing or
replacement (optics, alignment, incubation temperature failure,
Internal QC values having a bias
• Recent instrument malfunction, instrument failure soon after PT
specimen testing
• Assay settings (sample volume, reagent volume, delay time
incubation time no of readings to be taken etc. )
• improper reconstitution of QC materials, water quality, not
following manufacturer’s / PT provider’s instructions while
reconstituting, storing or handling reagents / QC materials
What type of Error is indicated
in green and red ?
Systematic Error
SAMPLE EQAS MONTHLY REPORT
Your result
SAMPLE EQAS MONTHLY REPORT
SAMPLE EQAS END OF CYCLE REPORT
SAMPLE EQAS END OF CYCLE REPORT
SAMPLE CAP EQAS REPORT
SAMPLE CAP EQAS REPORT
SAMPLE CAP EQAS REPORT
SAMPLE EQAS REPORT
Transcription error
Misplacing of specimens or interchanging results
of PT specimens
U1
U2
U3
31.3
13.1
1031.9
909.51
28.31
14.8
U3
U1
U2
Result - 226
Mean – 445
SDI – 4.34
ALT – 226 U/L
Mean – 445
SDI – 4.34
Analytical error – Calculation error
PT was repeated with 1 in 2 dilution as results were
high but the result was not multiplied by 2
Diluted result was sent
SAMPLE EQAS REPORT
SAMPLE EQAS REPORT
Erratic Results – Very poor precision and accuracy
Problem – Internal Controls wide SD due to various
reasons –
• Instrument not maintained & calibrated reagents
problems deterioration
• Analyte not calibrated
• Procedural problems
SAMPLE CAP EQAS REPORT
SAMPLE EQAS REPORT
1. Systemic error may have seeped in the system
anytime after the last EQAS sample reporting –
look at daily controls for any shift in values
2. May be a random error – Keep a watch on daily
controls and follow during next EQAS
3. Wrong sample was tested
4. Wrong preanalytical stage – reconstitution,
storage etc – look at values of other analytes
Are they with in acceptable limits of SDI and in the
same direction ?
SAMPLE CAP EQAS REPORT
SAMPLE EQAS REPORT
1.
2.
Systematic error – one showing a positive bias
and other a negative bias
Needs
Recalibration for analyte
Instrument maintenance
Internal QC Value Mean needs to be reset
SAMPLE EQAS REPORT
SAMPLE EQAS REPORT
1.
2.
3.
Fairly a good performance in terms of
accuracy and precision
Values on either side of mean No Bias
Values within =/- 0.5 SD