EXTERNAL QUALITY ASSESSMENT
this model is neither achievable nor appropriate in all situations. An analyte that is tightly regulated (eg sodium) may result in an APS target that is much narrower than can realistically be achieved with current technology. Conversely, an analyte with significant biological variation (eg cortisol), may result in an excessively wide APS target which is unable to detect deterioration in assay performance.
0.3 0.25 0.2 0.15 0.1 0.05 0 1 2 3 4 5 Overall mean (mmol/L)
45 40 35 30 25 20 15
10 5 0
0
1.8 1.6 1.4 1.2 1
0.8 0.6
0.4 0.2 0
0 10 20 Overall mean (mmol/L) 30 40 200 400 Overall mean (μmol/L) 600 800
2020 2021 2022 2023 2024
Minimum Desirable Optimal
0.8 0.9 1
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
1.5 3.5 5.5 Overall mean (mmol/L)
2020 2021 2022 2023 2024
Minimum Desirable Optimal
Top: Fig 1. Precision profiles for potassium (left) and urate (right). APS based on optimal EFLM total allowable error is possible for both analytes at certain concentrations.
Middle: Fig 2. Precision profiles for creatinine (top left), total cholesterol (top right) and glucose (botom left). APS based on desirable EFLM total allowable error is possible for all three analytes at certain concentrations.
Botom: Fig 3. Precision profiles for total calcium (left) and HDL-cholesterol (right). APS based on minimum EFLM total allowable error is possible for both analytes at certain concentrations.
0.06 0.05 0.04 0.03 0.02 0.01 0 1 1.2 1.4 1.6 1.8 2 2.2 Overall mean (mmol/L) 2.4 2.6 2.8 3
2020 2021 2022 2023 2024
Minimum Desirable Optimal
60 0.2 0.15 0.1 0.05 0 0 0.5 1 1.5 2 Overall mean (mmol/L) May 2026
WWW.PATHOLOGYINPRACTICE.COM 45 2.5 3 3.5
2020 2021 2022 2023 2024
Minimum Desirable Optimal
7.5 9.5 6 7 8
2020 2021 2022 2023 2024
Minimum Desirable Optimal
Model 3 – APS based on ‘state of the art’ Model 3 is based on the highest level of analytical quality currently available in clinical use (‘state of the art’) and defines acceptable APS as that can be achieved using existing methodologies. This model has been commonly used, due to ease of obtaining data and is a pragmatic method of demonstrating existing capability. However, if a significant number of methods exhibit bias, the resulting APS
80 70 60 50 40 30 20 10 0
150 250 350 450 550 Overall mean (μmol/L) 650 750
may in turn become too lenient, allowing poor performance to become established as the norm. In addition, Model 3 is not related to clinical practice, and APS may either be too lenient or too tight for the clinical utility of the test.
Choice of model The most appropriate model to use therefore depends on the nature of the analyte, the availability and quality of
2020 2021 2022 2023 2024
Minimum Desirable Optimal
2020 2021 2022 2023 2024
Minimum Desirable Optimal
SD (mmol/L)
SD (mmol/L)
SD (μmol/L)
SD (mmol/L)
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