2016, Volume 32, Number 3, Page(s) 171-177
A Six Sigma Trial For Reduction of Error Rates in Pathology Laboratory
Zeynep TOSUNER, Zühal GÜCİN, Tuğçe KIRAN, Nur BÜYÜKPINARBAŞILI, Seval TURNA, Olcay TAŞKIRAN, Dilek Sema ARICI
Department of Pathology, Bezmialem Foundation University School of Medicine, İstanbul, Turkey
Keywords: Pathology, Quality improvement, Six sigma
A major target of quality assurance is the minimization of error rates in order to enhance patient safety. Six Sigma is a method
targeting zero error (3.4 errors per million events) used in industry. The five main principles of Six Sigma are defining, measuring, analysis,
improvement and control. Using this methodology, the causes of errors can be examined and process improvement strategies can be identified.
The aim of our study was to evaluate the utility of Six Sigma methodology in error reduction in our pathology laboratory.
Material and Method: The errors encountered between April 2014 and April 2015 were recorded by the pathology personnel. Error follow-up
forms were examined by the quality control supervisor, administrative supervisor and the head of the department. Using Six Sigma methodology,
the rate of errors was measured monthly and the distribution of errors at the preanalytic, analytic and postanalytical phases was analysed.
Improvement strategies were reclaimed in the monthly intradepartmental meetings and the control of the units with high error rates was
Results: Fifty-six (52.4%) of 107 recorded errors in total were at the pre-analytic phase. Forty-five errors (42%) were recorded as analytical and 6
errors (5.6%) as post-analytical. Two of the 45 errors were major irrevocable errors. The error rate was 6.8 per million in the first half of the year
and 1.3 per million in the second half, decreasing by 79.77%.
Conclusion: The Six Sigma trial in our pathology laboratory provided the reduction of the error rates mainly in the pre-analytic and analytic
The “quality system” terminology originates from ISO
9000 Quality Standards that have been used in business life
and industry. A Quality system comprises organizational
structure, liabilities, procedures, operations and sources
that are required for quality management. This system has
also been modified for medical sciences1
medicine specialists emphasized the quality control model
in daily operations such as instrument calibration and
validation, reagent performance, linearity measurements,
and result output. Total quality management including
policies, written documents, organization, personnel,
equipment and safety has been applied in pathology
. Studies concerning quality
management improvement and standardization have also
taken place in the medical literature in Turkey3,4
Six Sigma have been used in industrial sciences for
regulating validity according to statistical analyses and
improving quality and minimizing errors in operation processes. Six Sigma was first used by a Japanese company
in the 70s for decreasing the error rate. The five main
principles of Six Sigma are: 1. Defining, 2. Measuring, 3.
Analysis, 4. Improving, and 5. Control.
It is suggested that Six Sigma can have positive impacts on
efficiency of laboratory safety2,5. Six Sigma approach in
laboratory medicine was first tested in pathology, and the
data of Q-Probes Program created by College of American
Pathologists are present in literature6-8.
Six Sigma is a procedure of detecting errors used for the
purpose of improvement under the roof of total quality
management. Six Sigma is a methodology targeting zero
error (3.4 errors per million events). This method has also
been used as a statistical term demonstrating a process'
degree of deviation from excellence. Six Sigma enables the
determination of the number of defects per million events
via monitorizing the processes. The error risk per million
events is called the “process Sigma level”. The process
Sigma level demonstrates the quantity of value that the process has deceived. There is a close relation between the
Sigma level and characteristics like error, cost of quality
loss (repetitions, time loss, wrong therapy, morbidity and
mortality, etc.) and efficiency per each test result. Elements
of the processes are analyzed according to the process Sigma
levels, and the area of improvement (AOI) is evaluated9.
Total quality management application in surgical pathology
laboratories is rapidly increasing. One of the main
principles in quality management is the analysis and
prevention of errors.
Errors in the pathology unit are classified as pre-analytic,
analytic and post-analytic. Pre-analytic errors include errors
during the process from entry to macroscopical analysis, and
analytic errors include errors from macroscopic analysis to
the reporting phase. Post-analytic errors include reporting/
diagnosis errors and the errors that occur after tissue
processing procedures, such as the tissue disposal process,
archiving, delivery of the reports, communication errors,
laboratory information system errors, comprehensibility of
the reports or misinterpretation errors. Most of the errors
in routine pathology processes are easily recognized before
sign out and are revocable; however, some are unidentified
irrevocable errors harmful to the patient. Reporting errors
in quality management is significant in terms of reducing
the repetition of an error10.
Several measurement and classification systems for errors
are introduced in surgical pathology. A system that focuses
on the clinical impact to the patient has been described by
Raab et al.11. In this system, errors were separated into
two categories; major and minor errors. Major errors were
subclassified in 4 categories causing no harm, near miss,
harm and unknown in measure of clinical severity. Minimal
harm was described as being associated with unnecessary,
further noninvasive testing, or a delay in diagnosis or
therapy of <6 months. The second category, mild harm,
represented unnecessary but invasive further testing,
a delay in diagnosis or therapy over 6 months, or minor
morbidity due to this delay. The third category, moderate
harm, included situations where moderate morbidity due
to a delay in therapy or unnecessary therapy occurred due
to the unjustified diagnosis. The last category, severe harm,
included loss of life, limb, or other body part, and any longlasting
morbidity of over 6 months11,12.
In our study, we aimed to examine all of major and
minor errors that had been encountered in our
department in a 1-year period and to assess the effect of
Six Sigma implementation in error reduction and process
In our pathology laboratory, the ISO 9001 program is
used as the standard program for quality management and
26,000 cases (16,000 biopsies and 10,000 cytology samples)
are assessed in a year. Errors concerning both biopsy and
cytology samples encountered between April 2014 and
April 2015 were recorded.
Pathology personnel (specimen registery personnel,
laboratory technical personnel, or pathologist) determined
the error, and recorded the characteristics of the error in a
follow-up form including his/her own errors. The standard
form is shown in Figure 1.
Error follow-up forms were examined by the quality control
supervisor, administrative supervisor and the head of the
department. The causes of errors were investigated and
revocable errors were corrected. Six Sigma principles were
applied to the evaluation of problems in our department
for 6 months.
In the defining phase, the causes and characteristics of
problems and the damages they caused were investigated.
The distribution of errors at pre-analytic, analytic and postanalytic
phases was examined in the measuring phase. In
the analysis phase, problem-solving activities were applied
regarding the prevention of the occurrence of errors.
Finally, the implementations for reducing all these errors
were initiated in the improvement phase. An example of
Six Sigma is presented in Figure 2.
Click Here to Zoom
|Figure 2: Implementation of Six Sigma method in
the cross-cassetting problem.
Regarding these errors, intradepartmental meetings were
held in monthly periods and error analyses were carried out.
Extradepartmental meetings with the responsible clinical
staff were organized in order to optimize sample delivery
procedures. In the intradepartmental meetings, where
the employees could express their problems and which
were based on the possible legal dimensions of the errors,
activities aiming to increase efficiency and to decrease
errors were performed. In these meetings, the employees
were given the opportunity to work in fields where they felt
most productive and solution offers about the problems
of employees were prioritized. With this purpose, not
only was a quality file created which all employees of the
pathology unit could access via their computers, but also
a platform was formed where errors, critical-diagnosis,
biopsy-cytology correlations, examination requests and the
number of denied samples were handled.
Additionally, a double-checking control system was
initiated in the phases of recording and macroscopy,
macroscopy and embedding, embedding and sectioning, and the other operations after sectioning and the delivery of
the slides. In this system, the technical personnel working
in successive steps, such as reception staff and macroscopy
staff, checked each other. For example, all of the recorded
specimens were listed and checked by two staff members
(delivery and reception staff). After recording, the list was
also double-checked by the reception and macroscopy
staff. In any problematic circumstance, the staff member
in charge called the quality control supervisor. The quality
control supervisor checked the materials and forms and
communicated with the corresponding specialists of the
clinical departments if needed. Hence all of the sub-units
were double-checked and connected to the quality control
unit (Figure 3).
The quality control supervisor also checked the quality of
processing, sectioning and staining by checking 10 random
slides prepared from different tissues every day.
The present immunohistochemistry staining machine was
replaced with a new and more automated device.
In the control phase, units with high error rates were
checked among employees.
Fifty-six (52.4%) of 107 recorded errors in total were at the
pre-analytic phase. Forty-five errors (42%) were recorded
as analytical and 6 errors (5.6%) as post-analytical.
Distribution of the errors with standard error classification
in preanalytical, analytical and postanalytical
phases are shown in Table I
. The number of errors differed
between each month and these are shown in Figure 4
highest number of errors (n=41) was detected in May 2014,
while the lowest number was detected in August 2014,
December 2014 and February 2015 (n=2). Eighty-nine
errors were detected in the first semiannual period, while
18 were detected in the second semiannual period.
Click Here to Zoom
|Table I: The distribution of the errors in pre-analytical, analytical and postanalytical phases
The overall error rate of our laboratory was 0.041% in 4.1
per million cases (107 errors per 26.000 cases) in one year.
The error rate was 6.8 per million in the first half of the year
and 1.3 per million in the second half.
Pre-analytic errors were subclassified into intradepartmental
and extradepartmental errors. The intradepartmental
error ratio was 58.3%, while the extradepartmental ratio
was 31.7%. No errors regarding the cytology interpretationbiopsy
correlation were recorded.
Of the recorded 107 errors, 2 errors were major errors. One
of the major errors was a pre-analytic phase error. A kidney
core biopsy in two fragments was delivered to the pathology
laboratory in frozen state in 10% formalin. Both routine
examination and direct immunofluorescein application
failed due to erroneous fixation and preservation. The
patient underwent an additional biopsy procedure. The
other major error was the discharge of a tonsillectomy
specimen before the completion of the reporting process.
This was noticed when the relevant pathologist wanted to
receive additional pieces from the specimen for further
evaluation. The specimen had accidentally been discharged
by the macroscopy assistant. Further evaluation was
available by application of an immunohistochemistry panel
to the present two blocks of the specimen in order to exclude
lymphoma. The final diagnosis of the case was chronic tonsillitis. The clinician of the patient was informed about
the failure and follow-up of the patient was recommended.
All of the remaining errors were minor errors and were
corrected before the pathology report finalization.
The initial immunohistochemistry device required 2 hours
of manual handling procedures. Technical problems were
also encountered regarding the software system, and
technical support was needed 4-5 times per month. The
workload of technical personnel was reduced by 50% by
moving to a more automated system that required 1 hour
of manual handling procedures.
When the first semiannual and second semiannual periods
were compared, the number of errors was 89 in the first
semiannual period while this number was 18 in the second
semiannual period, decreasing by 79.77%.
The Association of Directors of Anatomical and Surgical
Pathology (ADASP) recommends the usage of Quality
Assurance and Improvement plans and monitors in the
pre-analytic, analytic and post-analytic phases in order to
enhance patient safety, minimize error rates, ensure timely
delivery of reports and monitor physician competence13
. A formal root cause analysis is recommended for
incidents in which there is significant patient harm14
Dhir et al described a multiple-step algorithm of a formal
root cause in an incident in which there was an error in
specimen accessioning. After the identification of errors,
changes in procedures were implemented based on “oneby-
In our institute we initiated the Six-Sigma trial as a formal
root cause after the erroneous discharge of the tonsillectomy
specimen that is stated as a major error in our study.
Identification (“Defining”) of the probable causes of errors
provided the construction of the one by one accessioning
double-checking system in the laboratory. Thanks to the
implementation of this system, the error rates decreased by
Organization of the intradepartmental and extradepartmental
meetings provided training for the personnel on the
main principles of pathology laboratory processing. Pereira
et al. compared two 9-month periods during which a
monthly anatomic pathology quality and safety conference
was held and noticed a marked improvement in the second
time period with fewer cases of incomplete examination,
incorrect tumor classification, incorrect tumor staging and
clinically significant incorrect diagnosis16.
We observed the highest error rate (52.4%) in the preanalytic
phase. Pre-analytic component constitutes up to
80% of recorded cases based on a study revealing errors in a
ISO 9002:1994 certified clinical laboratory17. When the
cause of higher rate of pre-analytic errors was investigated,
the main reasons of errors in pathology unit were
considered to be the carelessness of recording personnel as
well as psychological burden due to being face to face with
the patient constantly.
In our study, we predominantly tried the Six Sigma
methodology in order to reduce the rate of errors in preanalytic
and analytic phases because of the high number
of errors assessed in these phases. This is a limitation
of our study because this system could have also been
applied for post-analytic errors including interpretation
errors. Another limitation is the lack of the examination
of the second review considerations of the consulted cases that were initially reported in our institute. Hence the
interobserver variability and the error rate of interpretation
results (if present) could be detected. Unfortunately we
were unable to reach the majority of the second review
results because of the lack of guidelines regarding the
interdepartmental consultation protocols.
All of the mentioned errors in this study were recorded
errors and it should be considered that unrecorded errors
might also be present. This situation may depend on
overlooking the errors or trying to solve the problems with
direct relations without recording. However, checking
the errors by recording through a transparent procedure
should be the target for a pathology laboratory with a lower
error rate. Finally, training and further studies regarding
the implementation of this system in Turkey will provide
more efficient pathology units with low error rates.
The authors want to thank Yücel Duduoğlu for her time
and technical support about the Six Sigma methodology in
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