Transcript Quality Control Terms - 36-454-f10

Quality Control Terms
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Gaussian Distribution
• Most of the Statistics we use are Dependent on
a Population following a Normal Gaussian
Distribution
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Normal Gaussian Distribution
• Most of the Statistics we use are Dependent on
a Population following a Normal Gaussian
Distribution
• Prepare Frequency Chart
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Normal Gaussian Distribution
• Most of the Statistics we use are Dependent on
a Population following a Normal Gaussian
Distribution
• Prepare Frequency Chart
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Normal Gaussian Distribution
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Gaussian Distribution
• Mean
• Median
• Mode
Average Value
Middle Value
Most Frequent Value
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Random Error
• Degree of scatter of values around the
mean value when repeat analysis's are
made on the same sample
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Precision
Reproducibility
• Statistical Terms used to measure
Precision
• Variance
• Standard Deviation (SD)
• Coefficient of Variation (CV)
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Most Labs run two controls
• One in the normal range
• One in the Abnormal range
• Sometimes a third control is used
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How are control ranges
determined?
• New lot of controls run many times while
old lot is still available.
• Need from 30 – 60 values
• Best to take some time
• Vary Techs and Shifts
• Avoid ranges that are too narrow
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Standard Deviation
• How spread out the sample values or how
dispersed they are from their mean
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Once ranges have been determined guide lines are set to
determine if a run should be reported
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Assume you are using two controls
Reject run and investigate if:
1 of 2 levels is > 3 S. D.
2 of 2 levels is > 2 S.D.
If 1 of 2 levels is > 2 S.D a second run in a
row
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Decisions based on Q.C. Data
• 1. A new lot of quality control material is run sixty times on
various shifts according to lab protocol. The mean is
determined to be 3.2 mg/dl with a 1 S.D. of 0.2 mg/dl. On
which of the following days is this control material “Out of
Control”.
Normal Control
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Monday
Tuesday
Wednesday
Thursday
Friday
3.7
2.9
4.1
3.3
3.1
Abnormal Control
( 5.5 – 6.5)
6.0
6.1
5.9
6.2
6.0
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Decisions based on Q.C. Data
• 1. A new lot of quality control material is run sixty times on
various shifts according to lab protocol. The mean is
determined to be 3.2 mg/dl with a 1 S.D. of 0.2 mg/dl. On
which of the following days is this control material “Out of
Control”.
Normal Control
( 2.8 - 3.6 )
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Monday
Tuesday
Wednesday
Thursday
Friday
Abnormal Control
( 5.5 – 6.5)
3.7
2.9
4.1
3.3
3.1
6.0
6.1
5.9
6.2
6.0
Answer Wednesday Normal Control > 3.8 (3SD)
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Clinical Decision
Is the patient getting better or worse ?
• The patient’s condition has changed when
the result has changed by more than 3
times the S.D.
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Clinical Decision
Is the patient getting better or worse ?
• Glucose
• 180
176
170
178
169
164
Mean 100
SD
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Clinical Decision
Is the patient getting better or worse ?
• Glucose Mean 100
SD
• 180
176
170
178
169
164
• 3 x5 = 15 180 -15 = 165
5
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Is the patient getting better?
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The patient was under therapy for kidney damage. The MD
ordered daily BUN to help determine any true clinical improvement
of the patient’s kidney function. The 1 S.D. for day to day QC for the
BUN method was 1.5 mg/dl. The patients daily BUN values were
as follows.
Monday
40.0
Tuesday
41.3
Wednesday
37.6
Thursday
40.3
Friday
35.0
Saturday
31.0
What is the “significant change” for this method? __________
On which day did a real change occur?
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Is the patient getting better?
• 2.
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The patient was under therapy for kidney damage. The MD
ordered daily BUN to help determine any true clinical improvement
of the patient’s kidney function. The 1 S.D. for day to day QC for the
BUN method was 1.5 mg/dl. The patients daily BUN values were
as follows.
Monday
40.0
Tuesday
41.3
Wednesday
37.6
Thursday
40.3
Friday
35.0
Saturday
31.0
What is the “significant change” for this method? ____4.5______
On which day did a real change occur?
Friday
40.0 – 4.5 = 35.5
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Is there a change in the method or
between two different methods?
• If the mean of method changes by more
than one SD investigation is needed.
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