Transcript Reference Ranges

QUALITY
ASSESSMENT
What is Quality Control?
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Quality Control in the clinical laboratory is a
system designed to increase the probability
that each result reported by the laboratory is
valid and can be used with confidence by the
physician making a diagnostic or therapeutic
decision.
Control Materials
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Control Values
Initially use manufacturer’s insert as guidelines
Clinical Laboratory Improvement Amendments
(CLIA) requires that each Lab perform their own
study to set limits
Recommend minimum 20 measurements
Over a 2 week period or 10 working days
Should be processed the same way as patient
samples
Investigate
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When results are out of control,
You must resolve the problem
Not just go past it without knowing the cause
Especially true for systematic errors
Stop bad habits!!!
Just repeating the control or just opening
a new control without investigating
 Most often eliminates the immediate
problem but not the real problem
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Develop good habits
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Inspect the charts
Random or systematic error?
Identify type of error with potential cause(s)
Relate possible causes to recent changes
Verify the solution and document!!
Control specimen is “out of control?”
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“Out of control” means that there is too much dispersion in your
result compared with the rest of the results – it’s “weird”
This suggests that something is wrong with the process that
generated that observation
Patient test results cannot be reported to physicians when there is
something wrong with the testing process that is generating
inaccurate reports
Remember … No information is better than wrong information
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Control specimen is “out of control?”
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Things that can go wrong and what to do:
ie. Corrective methods
 Instrumentation
malfunction ( fix the machine)
 Reagents deteriorated, contaminated, improperly
prepared or simply used up (get new reagents)
 Tech error (identify error and repeat the test)
 Control specimen is deteriorated or improperly prepared
(get new control)
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Random or systematic
13S and R4S usually associated with
random error
 22S, 41S, and 10X most often associated
with systematic errors
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LJ Control Charts
A LJ Control Chart depend on the use of IQC specimens and
is developed in the following manner:
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Put up the IQC specimen for at least 20 or more assay runs and
record down the O.D./cut-off value or antibody titre (whichever is
applicable).
Calculate the mean and standard deviations (s.d.)
Make a plot with the assay run on the x-axis, and O.D./cut-off or
antibody titre on the y axis.
Draw the following lines across the y-axis: mean, -3, -2, -2, 1, 2,
and 3 s.d.
Plot the O.D./cut-off obtained for the IQC specimen for
subsequent assay runs
Major events such as changes in the batch no. of the kit and
instruments used should be recorded on the chart.
Reference Ranges
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Results are most typically interpreted with respect to
the range of values found in normal, clinically healthy
individuals.
A result is considered abnormal if the value is less
than the lower limit of the normal range or is greater
than the upper limit.
Reference ranges are determined from measurements
on specimens from a large number (several hundred)
of clinically normal individuals.
Reference Ranges
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The reference range (or reference interval) for a laboratory
test is a reference point to determine whether a disease is
present or absent or if the patient is at risk for future disease
states.
This comparison may be used in monitoring the progression of a
disease or therapeutic drug levels.
Reference ranges may need to be established or confirmed
when a new analyte is measured, a new or different analytical
method is introduced, or there has been a significant reagent
modification by the manufacturer.
Laboratories are urged by manufacturers, as well as required
by (Clinical Laboratory Improvement Amendments ) CLIA , to
establish their own reference ranges.
Establishment of Reference Ranges
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Each lab must establish its own reference ranges
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Factors affecting reference ranges
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Age
Sex
Diet
Medications
Physical activity
Pregnancy
Personal habits ( smoking )
Geographic location ( altitude )
Body weight
Laboratory instrumentation ( methodologies )
Laboratory reagents
reference ranges are defined as being within 2 Standard Deviations
from the mean
Establishment of Reference Ranges
A minimum of 20 observations should be sampled in order to
obtain valid results ( but I’ll use just 6 to save time )
Determine the normal range for fasting plasma glucose using 6
people:
Sample 1 = 98 mg/dl
Sample 2 = 100 mg/dl
Sample 3 = 105 mg/dl
Sample 4 = 106 mg/dl
Sample 5 = 102 mg/dl
Sample 6 = 101 mg/dl
Mean
SD
2 SD
= 102 mg/dl
= 3.0 mg/dl
= 6.0 mg/dl
That means that the normal range for this group is from 102 ± 6,
or 94 – 108, which is ± 2.0 SD from the mean
Levey-Jennings QC Practice Exercise:
Cholesterol example where:
Control 1 has a mean of 200 mg/dL and standard deviation of 4.0 mg/dL.
Control 2 has a mean of 250 mg/dL and standard deviation of 5.0 mg/dL.
Prepare appropriate control charts and interpret the results.
Day
Control 1
Value
Control 2
Value
1
200
247
2
205
250
3
195
255
4
202
243
5
186
254
6
207
263
7
194
251
8
209
264
9
200
253
10
196
244
12s Rule
Violation
13s Rule
Violation
Accept(A),
Warning (W),
or Reject(R)?
Problem 1
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Calculation of Sensitivity and Specificity
Alpha-fetoprotein (AFP) levels are used by obstetricians to help
diagnose neural tube defects (NTD) in early pregnancy. For the
following data, calculate the sensitivity & specificity of AFP for
detecting NTD
NUMBER OF PREGNANCIES INTERPRETATION OF AFP FINDINGS
Problem 2
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For the following precision data, calculate the mean, standard
deviation, and coefficient of variation for each of the two
control solutions A and B. These control solutions were chosen
because their concentrations were close to medical decision
levels (X,) for glucose: 120 mg/dL for control solution A and
300 mg/dl. for control solution B.
Control solution A was analyzed daily, and the following values
were obtained:
118, 120, 121, 119, 125, 118, 122, 116, 124, 123, 117,
117, 121, 120, 120, 119, 121, 123, 120, and 122 mg/dL
Control solution B was analyzed daily and gave the following
results:
295, 308, 296, 298, 304, 294, 308, 310, 296, 300, 295.
303, 305, 300, 308, 297, 297, 305, 292, and 300 mg/dL