Short description of the categories of proficiency testing programs, management of external quality control assays, and evaluation of results

1. External Quality Control
Dr. Adel A. Elazab
Associate Professor of Clinical Pathology
Faculty of Medicine
Ain Shams University, Cairo, Egypt

3. Inter-laboratory comparisons and other
performance evaluations that may extend
throughout all phases of the testing cycle,
including interpretation of results;
determination of individual and collective
laboratory performance characteristics of
examination procedures by means of
interlaboratory comparison

4. A program in which multiple samples are
periodically sent to members of a group of
laboratories for analysis and/or identification,
in which each laboratory’s results are
compared with those of other laboratories in
the group and/or with an assigned value, and
reported to the participating laboratory and
others

5.  Introduced into laboratory medicine more than
60 years ago as an educational tool to address
observations that results for aliquots of the same
sample were different when measured by
different laboratories.
 PT/EQA programs have evolved in scope and
sophistication and are now an essential
component of a laboratory’s quality management
system.
 PT/EQA is a component of laboratory
accreditation requirements

8.  Ideal samples for a PT/EQA program would fulfill a
range of criteria:
◦ Stable for the conditions under which they will be
transported and stored
◦ Homogeneous across all the aliquots produced
◦ Have analyte concentrations that include the expected
clinical range
◦ Include appropriate sample types (e.g., urine, whole blood,
serum)
◦ Available in sufficient volume
◦ Inexpensive enough for cost not to be an impediment
◦ Behave in clinical laboratory measurement procedures in
◦ the same manner as patient samples
◦ Samples from a single donor or pooled samples from
multiple donors can be used

9.  Single-donor samples:
◦ Interfering substance may be
present that influences 1 or
more of the measurement
procedures.
 Pooled samples:
◦ Dilute an interfering substance
◦ Limited by interactions of
components such as serum
proteins or urine complexes
from different donors may
cause aggregation or
precipitation that necessitates
further processing and
potential modification of the
matrix

10.  Samples have traceable reference values (when
reference values are used)
 Behave like patient samples (commutability)
 The laboratory may also consider cost
 Similarity of PT samples to patient samples
 Method compatibility with peer groups
 Size of peer groups
 Frequency of challenges
 Timeliness and usefulness of reports
 Educational content
 Customer service

12.  category 1 programs are limited because of:
• Technical aspects such as a lack of reference measurement
procedures, absence of certified reference materials, inability to
prepare commutable samples;
• Practical considerations such as the difficulty of preparing
samples covering the full measuring interval and the complicated
logistics of preparation and distribution of fresh or frozen
samples;
• Psychological limitations such as lack of awareness of the quality
factors important in PT/EQA or unwillingness to adopt these;
• Economic concerns because distributing commutable samples in
sufficient quantity and providing target values with reference
measurement procedures is expensive

13.  PT samples should be tested in the same manner as
patient samples, to the extent possible
 Some laboratories may improperly test PT samples
differently from patient samples, by repeat testing of
PT samples when patient samples are tested only
once, or by having a specific analyst test PT samples
rather than rotating PT testing among all the
personnel who perform patient testing.
 There should be no attempt to produce “best” results
by replicate analysis or testing immediately following
internal QC or recalibration

14.  The core content of the result report should
resemble as closely as possible the content of
a routine clinical result report
 If the usual report is deemed inappropriate
for a PT report, it may equally be
inappropriate for a clinical report
 A copy of all PT reports should be retained
within the laboratory in order to verify the
information handling by the PT provider.

15.  Sending a set of samples from an organizing body to a group of
participating laboratories for measurement of 1 or more analytes
present in the samples
 Samples are intended to simulate the clinical samples usually
measured
 Laboratories are not informed of the analyte concentration or
activity in a particular sample
 Timely schedules for running and reporting results are included
 Laboratory perform measurements in the same manner as for
patient samples
 Results for the samples are returned to the PT/EQA organizer for
evaluation of conformance to the expected results

16.  The organizer prepares a report that includes:
◦ the results reported by a laboratory
◦ the method used for the measurements
◦ the target values expected for each analyte
◦ evaluation of whether the individual laboratory’s results
met the performance requirements
◦ Reports may also include evaluation of the performance of
the various measurement procedures used by the
participants
 The laboratory evaluates its performance according
to the provider report

17.  Limits or quality standards around the target value are
established against which performance can be assessed by:
◦ Regulatory: wider like US CLIA, German Rili-BAeK
◦ Statistical: ± 2-3 SD
◦ Clinically-based: on a difference that may affect clinical decisions or on
biological variation
 Total error limits including bias, imprecision, and analytical
nonspecificity can contribute to the variation in a single result
 Have different limits to separately assess bias and imprecision
when replicate samples are included
 PT/EQA limits are set as a minimum standard to identify results
that indicate poor performance. Thus, meeting these standards
may not indicate that performance is optimal nor that
performance meets all clinical needs

18.  Determines the accuracy by comparing PT/EQA results to
those from a reference measurement procedure or from a
designated comparison method or to an all-participant (or
all-method) mean/ median. This arrangement is now
referred to as accuracy-based evaluation
 Assess agreement with other measurement procedures
and imprecision among all methods as well as within a
method group
 Peer group evaluation provides valuable information to
assess quality, verifying that a laboratory is using a
measurement procedure in conformance to the
manufacturer’s specifications and to other laboratories
using the same technology

22.  PT/EQA result represents 1 point in time and will
occasionally be a random error
 Repeat the measurement using a stored aliquot
of the PT/EQA sample (assuming the measurand
was stable on storage) to confirm if the problem
has persisted or to conclude that the problem no
longer exists and the original unacceptable result
was a random event, and therefore no corrective
action is indicated. If the repeated result is still
unacceptable, the laboratory conducts further
investigation to identify the root cause, and then
initiates corrective action

23. • Gather data related to the testing event to
include records of calibration, reagent use, QC
results, and maintenance procedures;
• Obtain other data on assay performance, e.g.,
previous PT/EQA results and relevant patient
data;
• Identify the root cause of the error;
• Take corrective action and preventive action if
indicated;
• Monitor the success of the corrective action;
• Document the investigation and the corrective
action.

24. • Was the testing material received in satisfactory
condition?
• Was the appropriate sample tested?
• Were procedures for sample preparation followed?
• Was the appropriate method used for analysis?
• Was the method performed according to
documented procedures?
• Were appropriate reagents and controls used?
• Was equipment operated according to documented
procedures?

25. • Was equipment appropriately maintained?
• Was QC acceptable at the time of testing PT
samples?
• Were results interpreted appropriately?
• Has this problem occurred previously with PT
samples? Are data consistent with previous PT
distributions? Is there a trend leading to failure or is
the current set completely unexpected?
• Did repeat testing on the properly stored residual
sample produce similar results?
• Were patient results acceptable at the time of PT
testing?

26. 1. Clerical error;
2. Methodologic problem;
3. Equipment problem;
4. Technical problem;
5. Problem with proficiency testing materials;
6. Problem with evaluation of results; and
7. No explanation after investigation.

27. • result was not correctly transcribed from the
instrument tape or read-out to the report
form;
• the PT sample was mislabeled;
• an incorrect instrument or method was
reported on the form;
• incorrect units were reported;
• a decimal point was misplaced; or
• an incorrect reporting code was selected on
the report form.

28. • no written procedure (method) for staff to follow;
• procedure steps inadequately, incompletely, or
incorrectly described;
• problem in manufacture of reagents or reference
materials;
• imprecision due to result being close to detection
limit of method;
• imprecision due to variation between reagent lots;
• incorrect assignment of calibrator value;
• calibration is unstable;

29. • inadequate quality control method; e.g.,
− QC material not relevant to analyte concentration, or
− inappropriate QC rules or limits;
• result not within measuring range (linearity) for
instrument or reagent system;
• method is biased;
• method lacks sensitivity;
• method lacks specificity;
• carry-over from previous sample(s);
• inappropriate incubation conditions (time,
temperature, and/or atmosphere);
• method used without validation;
• inappropriate reference intervals applied

30. • obstruction of instrument tubing/orifice by clot or protein;
• misalignment of instrument probes;
• problem with instrument data processing functions;
• problem in manufacture of reagents or reference
materials;
• problem with instrument settings specified by
manufacturer;
• automatic pipettor not calibrated to acceptable precision
and accuracy;
• equipment malfunction;
• errors or omissions in programming of equipment
software applications; and
• scheduled instrument maintenance not performed
appropriately.

31. • failure to follow recommended instrument
function checks (e.g., temperatures, blank
readings, pressures);
• incorrect reconstitution or storage of
reference materials or reagents;
• improper reconstitution, preparation, or
storage of PT material;
• delay in testing after reconstitution of PT
material, causing evaporation or
deterioration;
• failure to follow written procedures;

32. • failure to follow PT instructions;
• failure to act on QC results that indicate a
method problem;
• pipetting or dilution error;
• calculation error;
• contamination of PT sample during
processing

33. • differences between PT samples and patient
samples;
• sample deteriorated in transit (if time- or
temperature-sensitive)
− bacterial contamination
− hemolysis
− nonhomogeneous sample;
• sample contains interfering factors (which
may be method-specific).

34. • inappropriate peer group;
• inappropriate target value from
nonhomogeneous testing material or
lingering [“masked”] outliers
• inappropriate evaluation interval with an
extremely precise method, the acceptable
range may be much narrower than needed for
clinical usefulness
• incorrect data entry by PT provider.

35. An investigation fails to reveal an explanation
for an unacceptable PT result 19 to 24% of
the time

40.  Split-Sample With Another Laboratory
 Internal Split-Sample Procedures
 Audit-Sample Procedure
 Analysis of Manufacturer’s Product Calibrator or
Trueness Control Material
 Analysis of Interlaboratory Quality Control Data
 Averages of Patient Data

41.  Reference Intervals
 Reevaluation of Interpreted Results
 Direct Observation of Technique-Dependent Tests
 Clinical Correlation Studies
 Government and University Interlaboratory
Comparison Programs
 Analysis of Data From Qualitative Alternative
Assessment Procedures

42. YOUR VALUABLE QUESTIONS