Transcript I. Introduction to Laboratory Medicine

Unit #7 - Basic Quality
Control for the Clinical
Laboratory
Cecile Sanders, M.Ed.,
MT(ASCP),
CLS (NCA)
Unit #7 - Basic Quality Control
for the Clinical Laboratory
 Introduction
– The results obtained from laboratory
analyses are used to diagnose,
prescribe treatment, and/or monitor
the health or progress of the patient.
Since such importance is placed upon
test results, they must be as reliable
and accurate as possible.
Unit #7 - Basic Quality Control
for the Clinical Laboratory
 Elements
of a Total Quality Control
Program (may be referred to as QC,
QA, or TCM, among others)
–
–
–
–
–
–
Current procedure manual
Documentation
Qualified personnel
Fire and safety program
Use of appropriate standards and controls
External proficiency testing
Unit #7 - Basic Quality Control
for the Clinical Laboratory

Standards and Controls
– Standard
A
substance that has an exact known value and that,
when accurately weighed or measured, can produce a
solution of an exact concentration
 Also called “reference materials”
 Not usually used on a daily basis
 Used to calibrate new instruments, recalibrate
instruments after repair, at manufacturer’s
recommended intervals, or if a method is out of
control
Unit #7 - Basic Quality Control
for the Clinical Laboratory
– Control
A
solution that contains the same constituents
as those being analyzed in the patient sample
 Most are commercially produced from pooled
sera
 The manufacturer has analyzed each lot of
serum for a variety of test components and the
expected range of assay values for each
component is provided to the laboratory when
shipped
Unit #7 - Basic Quality Control
for the Clinical Laboratory
– Control (cont’d)
 Controls
are analyzed with each patient test or
batch of tests and the results are compared
with the manufacturer’s range of values
 For most tests, a “normal” control and an
“abnormal” control are analyzed with each
patient test or batch of tests
 Results are plotted on a QC record called a
Levey-Jennings Chart
Unit #7 - Basic Quality Control
for the Clinical Laboratory
Example of Levey-Jennings Chart
Unit #7 - Basic Quality Control
for the Clinical Laboratory
 Accuracy
- closeness of a result to the
actual value
 Precision – “reproducibility” or closeness
of values to each other
Unit #7 - Basic Quality Control
for the Clinical Laboratory
Unit #7 - Basic Quality Control
for the Clinical Laboratory
 Mean,
Variance and Standard Deviation
– these must be determined for each
test or analysis to be used for quality
control
– Mean ( ) = the average for a set of values
– Standard Deviation (s or SD) = a measure
of the scatter of the sample values around
the mean and is derived from the
calculation of the variance (s2)
Unit #7 - Basic Quality Control
for the Clinical Laboratory
– Calculating the
variance
Unit #7 - Basic Quality Control
for the Clinical Laboratory

Using Standard
Deviation in QC
– When a set of values
with a normal
distribution is
plotted on a graph,
the distribution of
the values around the
mean forms a
Gaussian Curve (also
known as a normal
frequency or normal
distribution curve)
Unit #7 - Basic Quality Control
for the Clinical Laboratory
 Using
Standard Deviation in QC (cont’d)
– Clinical laboratories establish the standard
deviation for each laboratory test or
analysis
– A common choice is plus or minus 2 s or SD,
most often written as ± 2 s or ± 2 SD
Unit #7 - Basic Quality Control
for the Clinical Laboratory
– The mean and ± 2 SD
are plotted on a
Levey-Jennings chart
(green line is )
Unit #7 - Basic Quality Control
for the Clinical Laboratory
Every time the control is run, the value is
plotted on the L-J chart
Unit #7 - Basic Quality Control
for the Clinical Laboratory

As long as the control value are between the ± 2
SD lines on the L-J chart (in this case, the lines
are colored yellow), the control values are “in
control”
Unit #7 - Basic Quality Control
for the Clinical Laboratory

On the L-J chart below, note that values for days
5, 8, 11, 17, 25, and 27 are outside the ± 2 SD
yellow lines. Therefore, controls on these days
are “out of control”
Unit #7 - Basic Quality Control
for the Clinical Laboratory
Levey-Jennings
Chart with Values
“In Control”
Control Values

Levey-Jennings Chart
Control Range 80-100
100
95
90
85
80
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Days or Runs
Unit #7 - Basic Quality Control
for the Clinical Laboratory
Trend
– An uninterrupted rise
or decline away from
the mean
– When the 6th value
with a rise or decline
is reached, the values
are “out of control”
Levey-Jennings Chart
Control Range 80-100
Showing Trend 5 through 10
Control Values

100
90
80
1
2
3
4
5
6
7 8
9 10 11 12 13 14
Days or Runs
Unit #7 - Basic Quality Control
for the Clinical Laboratory
Shift
– An uninterrupted
shift of values on one
side of the mean
– When the 6th value on
one side of the mean
is reached, the values
are “out of control”
Levey-Jennings Chart
Control Range 80-100
Showing Shift 5 through 10
Control Values

100
95
90
85
80
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Days or Runs
Unit #7 - Basic Quality Control
for the Clinical Laboratory
The use of a single control is for very basic
laboratory testing in waived CLIA
laboratories
 In moderately and highly complex CLIA
testing laboratories two controls (usually a
“normal” and an “abnormal”) must be run with
each test or batch of tests and Westgard
Rules apply
 Westgard Rules are beyond the scope of this
course and will be covered in advanced MLT
courses
 http://www.westgard.com/mltirule.htm

Unit #7 - Basic Quality Control
for the Clinical Laboratory
Whenever a patient’s test or a batch of tests
are performed and the control(s) is “in
control”, the values obtained for the patient
test(s) are determined to be “acceptable” and
can be released to the doctor as accurate.
 Whenever a patient’s test or a batch of tests
are performed and the control(s) is “out of
control”, the values obtained for the patient
test(s) are determined to be “not acceptable”
and CANNNOT be released to the doctor as
accurate until the problem is identified and
resolved.

Unit #7 - Basic Quality Control
for the Clinical Laboratory

Errors in Laboratory Testing
– May occur at several points
 Preanalytical
– errors made prior to testing the
patient specimen (Ex. Misidentifying the patient
during blood collection, mishandling specimen, etc.)
 Analytical – errors made in the testing process (Ex.
Error in procedure, instrument trouble, etc.)
 Postanalytical – errors made after testing (Ex.
Typing the wrong results in the computer, failure to
notify physician in a timely manner, etc.)
Unit #7 - Basic Quality Control
for the Clinical Laboratory
 Errors
in Laboratory Testing (cont’d)
– Random or Systematic
 Random
Errors – cannot be absolutely identified
(Ex. Differences in techniques between
workers, specimen characteristics, etc.)
 Systematic Errors – variation that may make
results consistently higher or lower than the
mean value for a control (Ex. Trouble with the
instrument, deteriorated reagents, etc.)
Unit #7 - Basic Quality Control
for the Clinical Laboratory

Errors in Laboratory
Testing (cont’d)
– Our goal is to
identify systematic
errors and eliminate
them!

My control results
are “out of control”!
Now what?
Unit #7 - Basic Quality Control
for the Clinical Laboratory

The following steps should be taken in order
when the control results are “out of control”
1. Look at the procedure and evaluate your
technique (Ex. Did I use the right lot #? Are my
reagents in date? Did I make an error in the
procedure?)
2. Re-run the procedure, including controls
3. If results are still out of control, clean/perform
maintenance on equipment and/or open a new
batch of reagents
4. Contact supervisor
Unit #7 - Basic Quality Control
for the Clinical Laboratory
ALWAYS, ALWAYS,
ALWAYS:
DOCUMENT
THE PROBLEM
AND
CORRECTIVE
ACTIONS
TAKEN!!!!!
Unit #7 - Basic Quality Control
for the Clinical Laboratory
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