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Health care delivery is no longer a simple process of examining the patient
and giving him a prescription. Over the years there has been rapid expansion
in the various branches of health care services. As part of this expansion
process and explosion of scientific medical knowledge, laboratory diagnosis
has gained tremendous importance in today's practice. Through the use of
quality control (QC) the laboratory can ensure that the results being issued
by it are reliable enough to allow decisions to be taken with confidence. QC
is the study of those errors which are the responsibility of the laboratory,
and of the procedures used to recognize and minimize them. Incorrect
laboratory results may lead to wrong management decisions with possible fatal
results. The reliability of laboratory results is therefore most important.
It is not sufficient to ‘think’ that ‘my’ results are satisfactory.
This has to be proved with scientific evidence. Laboratory personnel must
know that QC is an obligation to the patient, that it is designed to give the
analyst confidence in the methods used and that its purpose is not to find
scapegoats or to punish those making mistakes.
 Quality Manual
Towards achieving quality, international accreditation
programmes strongly recommend the production of a quality manual by the
laboratory.
The quality manual of a laboratory is a document or a
set of documents describing the organizational structure, responsibilities,
procedures and processes by which the laboratory achieves its objectives and
gains confidence in its work. The manual is indispensable for achieving and
maintaining good overall quality. Furthermore, the preparation of a quality
manual may induce the laboratory to improve quality. Even a non-mandatory
quality manual may be a valuable document for a clinical laboratory in
demonstrating to clinicians and the hospital administration a commitment to
quality.
"The laboratory shall define and document its
policies and objectives for, and its commitment to, good laboratory practice.
The hospital management shall ensure that these policies and objectives are
documented in the quality manual and communicated to, understood by, and
implemented by all laboratory personnel concerned. The quality manual
contents are as follows
 Contents of quality manual
These are:
 Quality Policy and Quality System
Organization
Quality Control
Personnel
Accommodation and Environment
Equipment
Reference Materials
Test Procedures
Handling of Reagents
Sample Collection, Storage and Disposal
Maintenance of Records
Laboratory Reports and Despatch
of Reports
Quality policy
The aim of the laboratory is to provide clinically
useful information through laboratory measurement of samples from patients,
taking into account the allocated resources.
The quality policy is implemented by the following
means;(2)
Proper sample collection, stabilization,
transport, sample preparation and identification.
Reliable analytical work so that systematic
and random errors do not exceed specified limits.
Turn-around time within specified limits for
routine and emergency measurements, and for rare routine measurements.
Data reported in a clear form and supplemented
with relevant information, including reference intervals to allow reliable
clinical interpretation.
Appropriate communication to the clinicians so
that the results will be interpreted correctly and logically integrated into
further (clinical and laboratory) evaluation of the patients, and that the
clinicians become aware of unexpected problems and errors.
Standard operating procedures
The preparation of test procedures comes under the broad
heading of Standard Operating Procedures (SOPs). SOP is a clear, concise and
comprehensive written instruction of a method or procedure which has been
agreed upon and authorized as the operating policy of the department.
In general, SOPs, which mainly contain detailed
descriptions of each analytical method, are essential for maintaining the
same analytical quality over a long period of time. The procedures are a
prerequisite to correct transfer of methods from one laboratory to another.
The contents of SOP are as follows:
Introduction
Principle of method
Specimen types, collection and storage
Reagents, standards and control - preparation
and storage
Equipment, glassware and other accessories
Detailed procedure
Calculations, calibration curve
Analytical reliabilities – (QC and Statistical
assessment)
Hazardous reagents
Reference range and clinical interpretation
Limitations of method (e.g. interfering
substances and troubleshooting)
References
Date and signature of authorization
(Effective date + Schedule for review)
Laboratory errors
Analytical errors are classified into random errors and
systematic errors. It is clear that random errors indicate poor precision
while systematic errors indicate poor accuracy. A few examples of random
errors are pipetting error, transcription error,
wrong sample numbering and labelling, and
fluctuating readings on the colorimeter. Systematic errors could occur due to
wrong procedure, incorrect standard and calibration procedure.
Errors can occur in any of the limb of the cycle of
events taking place in a hospital, starting from the physician examining the
patient and back to the physician (pre-analytical/
analytical/post-analytical).
The physician, after examining the patient, decides and
orders a test, and collects and transports the patient’s samples; this
constitutes the pre-analytical limb of the cycle of events. In the analytical
limb the sample is received by the laboratory and analysed.
The post-analytical limb consists of the transfer of the result to the
physician and a meaningful interpretation of the laboratory data by the
physician, followed by necessary action.
Definition:
Accuracy is the degree of agreement between a
measured value and its ‘true/consensus’ value. On the contrary, inaccuracy,
which is represented by analytical bias, is defined as the % of the
difference between the measured value and the ‘true’ value over the true value.
Therefore, good accuracy means least analytical error.
Precision refers to reproducibility. It refers
to the agreement between replicate measurements. It is quantitatively
expressed as the standard deviation (SD) or more precisely as percent
coefficient of variation (CV), which is defined as SD times 100 divided by
the mean value of the results in a set of replicate measurements. Therefore,
good precision means least CV.
Pre-analytical
The pre-analytical system shall take care of the
following aspects(3),as each can have a major effect
on the accuracy of the result:
Patient preparation
Request forms
Specimen collection, containers, labelling and phlebotomy equipment and procedure
Specimen transport
Specimen preparation
Specimen storage
Analytical
The following aspects(3) shall be monitored, evaluated,
implemented and maintained to ensure the accuracy and precision of the test
carried out:
Quality of distilled water
Calibration of measuring and testing
instruments including balances, thermometers, incubators, waterbaths,
autoclaves, centrifuges and semi-automatic pipettes, and regular servicing
and maintenance of equipment.
It is essential to use a standard calibrator which is
traceable to national/international reference material. The laboratory shall
obtain evidence of traceability to the reference material from the supplier.
Precision can be maintained through the use of suitable QC material, either
commercial or prepared in-house. The QC material should be analysed at predetermined intervals along with patient
samples to monitor systematic and random errors. Such QC material shall also
be traceable to a national/international certified reference material so that
the accuracy of measurements can be monitored.
All data relating to the laboratory’s internal QC
practices and performance in external quality assessment schemes (scoring,
ranks, etc.) shall be recorded, reviewed and corrective actions implemented.
Stability
of reagents
Laboratory personnel should be aware that the stability
of all reagents kept at room temperature will go down from the stated values
if the temperature exceeds 350C.
Use
of calibration graphs
A fresh standard curve should be carried out for the
analyses described in this manual whenever:
the calibrator is changed
new reagents are introduced
problems with QC are encountered
Post-analytical
In order to avoid transcriptional errors in the results
of the test, the reporting/signatory technicians shall verify the results
entered manually or through on-line instrument interfaces before the results
are reported or despatched.
Rectification
of laboratory errors
It is therefore essential to continually ask the
following questions.
Is there an analytical error?
If so, what type of error is this?
What could have been the causes for this
error?
How to rectify this error?
It is important to identify analytical errors and
classify them as either random or systematic errors. Towards this end, the
laboratory should implement internal QC procedures. This involves preparation
of a QC pool, either human or bovine, quantification of unavoidable
laboratory errors, construction of Levey-Jennings chart and daily analysis of QC along with
every batch of patients’ samples.
Preparation of QC pool
Ethanediol stabilized liquid serum QC pool
has been established in the authors’ laboratory (4) based on the
WHO method (5). This procedure is applicable to both pooled human
serum as well as bovine serum. This preparation is economical and appropriate
for use in the laboratories in developing countries.
Use of
patients’ s era
A serum pool can be prepared by salvaging the extra
serum from leftover patients’ samples after analysis. Samples that are
significantly haemolysed or lipemic
or icteric should be excluded. Similarly, samples
that show positive tests for HIV antibodies and Hbs
antigen should also be excluded. In view of the dangers in handling
infectious blood samples, use of animal-based QC pool is recommended.
Use of bovine serum
Collect about 2-3 litres of
fresh bovine blood in a 5-litre clean plastic bucket. Allow to clot at room
temperature for about 30 minutes.
Slice the clot into small pieces using a sharp knife and
leave the bucket at 2-80C for 12 hours to enable the serum to ooze
out. Decant the crude serum into a one litre beaker
or flask.
Transfer this crude serum into several glass centrifuge
tubes (size 15 x 120 mm) and then centrifuge for 10 minutes at 3500 rpm and
decant the clear serum into a clean bottle.
Transfer one litre serum into
a one-litre plastic bottle.
Mix the contents well and store the container at –200
C for 12 hours or until frozen.
While monitoring day-to-day laboratory performance with
internal QC, it is preferable to use different levels of QC materials to
cover the entire pathological ranges. Therefore, methods of preparation of
three levels of QC (low, normal and high) are described below.
If the preparation of all three levels of QC pool is not
possible, it is essential to make use of at least one level, viz. normal
level.
The procedures described below for the preparation of
all three QC levels are applicable to both human serum and bovine serum.
Preparation
of normal-level QC serum
Remove the container from the freezer and fix it upside
down over a one-litre plastic measuring cylinder.
Collect the first 830 mg, which will be rich in all constituents. Add 150 ml
of ethanediol to this and mix well. Take an aliquot
and measure the levels of various analytes. Use 20
ml distilled water to dissolve the various substances that will be added to
the serum in order to increase the levels of these to the desired normal
levels. Total volume = 830+150+20 = 1000 ml
The QC serum thus prepared will contain 15% (V/V) ethanediol.
Preparation of high-level QC serum
Freeze one litre of clear
serum at -200C. Remove the container from the freezer and fix it
upside down over a one-litre plastic measuring
cylinder. Collect the first 700ml, which will be more concentrated and rich
in all constituents. Add 127.5 ml of ethanediol to
this and mix well. Take an aliquot and measure the levels of various analytes. Use 22.5 ml distilled water to dissolve the
various substances that will be added to the serum in order to increase their
levels to the desired levels. Total volume = 700 +127.5+22.5 = 850 ml.
The QC serum thus prepared will contain 15% (V/V) ethanediol. 
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