June 1997
APPLICATION OF THE
MONTH
EXAMPLE PLANNING
APPLICATIONS USING EUROPEAN BIOLOGIC
GOALS:
Cholesterol and glucose
Recommendations on how to use the QC Validator program with the European
biologic goals for imprecision and inaccuracy have been published, along
with some example applications [1]. Two additional applications are illustrated
here to facilitate comparisons between the European biologic goals, the
CLIA analytical quality requirements for total error, and the clinical
quality requirements for medically important changes.
Go back to the cholesterol application
Glucose:
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Glucose application
1. Define the Quality Requirement
For glucose, the EGE-Lab specifications are 1.9 % for bias (interim 4.4%)
and 2.2 % for imprecision. The total error calculated using the interim
bias specification is 8.0% (1.65*2.2 % + 4.4% = 8.0 %).
2. Evaluate the analytical factors
Given a POC method that has stable performance of smeas=2.44%
and biasmeas=2.7%(such as discussed earlier in the QC
planning application for a point-of-care glucose test). The stable
imprecision is a little bit too large, but the stable inaccuracy is well
with the interim specification.
3. Enter parameters in computer program
| The input parameters for the QC Validator program are shown here. A
decision level of 90 mg/dL corresponds to 5.0 mmol/L, which is used here
to be consistent with the earlier example that used a clinical quality
requirement. |
|
4. Obtain OPSpecs chart
Candidate control procedures are selected by pressing the "From Table"
button and choosing individual control rules and N's from the long list
included in the program. For European labs, mean/range rules are of interest
and are included in the list chosen.
5. Assess probabilities of rejection
| The stable imprecision itself is not acceptable, but the stable bias
is less than the interim goal. When the calculated total error is used
to assess QC design, the OPSpecs chart for TEa of 8% and 90%
AQA shows the difficulty of assuring the quality required by the European
biologic goals. The operating point (that represents smeas of
2.44% as the x-coordinate and biasmeas of 2.7% as the y-coordinate)
is far to the right of the allowable limits of imprecision and inaccuracy
for the candidate QC procedures with Ns of 2. |
|
6. Select the control rules and numbers of control
measurements, N
For the glucose method is not possible to assure the quality required by
European biologic goals.
7. Adopt a Total QC Strategy
In a situation
like this, one must stress the non-statistical elements of QC, such as
preventive maintenance, instrument function tests, and personnel training.
You should use a low TQC strategy that emphasizes non-statistical
components.
In this table, the relative number of x's indicate the relative emphasis
on the different components in a Total QC strategy. SQC stands for Statistical
QC. QI stands for Quality Improvement. Other QC includes preventive maintenance,
instrument function checks, performance verification tests, and patient
data QC algorithms.
8. Reassess for changes in performance
Even if bias were reduced to zero, the imprecision would be too great;
a method CV of 1.8% or better is needed to assure the desired quality will
be achieved in routine testing (as shown by the x-intercepts of the OPSpecs
lines for the candidate QC procedures). By comparison, the US CLIA analytical
quality requirement is 10% and would require a method imprecision of 2.3%
or better for these same N=2 QC procedures.
For the clinical quality requirement considered earlier in the glucose
POC application, this method could actually be controlled using x0.01/R0.01
rules, the 12.5s single rule, or the 13s/22s/R4s
multirules with Ns of 2; a method with a CV as large as 3.6% could be tolerated
if bias were zero.
For further discussions and comparisons of the European biologic goals,
the CLIA allowable total errors, and clinical quality requirements, see
references 2-4.
Return to the cholesterol application
References
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1. Hyltoft Petersen P, Ricos C, Stockl D, Libeer J-C, Baadenhuijsen H,
Fraser CG, Thienpont L. Proposed guidelines for the internal quality control
of analytical results in the medical laboratory. Eur J Clin Chem Clin Biochem
1996;34:983-989.
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2. Westgard JO, Seehafer JJ, Barry PL. European specifications for imprecision
and inaccuracy compared with operating specifications that assure the quality
required by US CLIA proficiency-testing criteria. Clin Chem 1994;40:1228-1232.
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3. Westgard JO, Seehafer JJ, Barry PL. Allowable imprecision for laboratory
tests based on clinical and analytical test outcome criteria. Clin Chem
1994;40:1909-1914.
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4. Hyltoft Petersen P, Fraser CG. Setting quality standards in clinical
chemistry: Can competing models based on analytical, biological, and clinical
outcomes be harmonized? Clin Chem 1994;40:1865-1868.Page references for
CLIA QC requirements
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please e-mail us!
Submit your laboratory data and you may receive a free quality control
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Past QC Applications:
Copyright © 1997. All rights reserved.
WesTgard® Quality Corporation, 7614 Gray Fox
Trail, Madison WI 53717
Call 608-833-4718 or e-mail westgard@westgard.com
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