Uncertainty of Measurement Application to Laboratory Medicine 鏡檢組 蔡雅雯 2014/09/09

Transcription

1 Uncertainty of Measurement Application to Laboratory Medicine 鏡檢組 蔡雅雯 2014/09/09

2 Objectives Definitions Methodology Equation of Measurement Uncertainty Measurement Uncertainty Goal Examples

3 Uncertainty of measurement (UM) Definitions 意即量測系統的不精密性 量測系統在可能發生的各種變因 ( 不同次操作 校正 維修 更換試劑批號等 ), 產生量測結果的變異程度, 用標準差 SD CV 來表示 UM=Intermediate Imprecision. MU -2sd +2sd Result Bias of procedure Reference value, inter lab comparison

4 ISO 15189: 定量量測值的量測不確定度實驗室應決定在檢驗階段的每項量測程序其用於報告病人樣本的定量量測值之量測不確定度 實驗室應明訂每項量測程序其量測不確定度的性能要求, 並定期審查量測不確定度的估計值 附註 : 可在中間精密度條件下, 採取量測品管物質的量值 須包括量測程序中合理可能的常規改變 當實驗室解釋量測的量值時, 應考慮量測不確定度 實驗室應為使用者提供量測不確定度估計值

5 Guidelines Clinical and Laboratory Standards Institute C51A. Expression of Measurement Uncertainty in Laboratory Medicine. Eurochem/CITAC Quantifying Uncertainty in Analytical Measurement, 3 rd. National Pathology Accreditation Advisory Council, Australia Requirements for the Estimation of Measurement Uncertainty. Singapore Accreditation Council, Singapore. (2013). A Guide on Measurement Uncertainty in Medical Testing.

6 Sources of Uncertainty Uncertainty of Measurement

7 Methodology The bottom-up approach 4 Comprehensive categorization of the measurement in which each potential source of uncertainty is identified and quantified. Provides the combined standard uncertainty of the result Not suitable for routine use The top-down approach Uses available laboratory performance information, such as method validation, intra-laboratory and inter-laboratory data The estimates of overall uncertainty associated with the result produced by a given measuring system.

8 Steps Define the measurand of measurement procedures a) quantity intended to be measured b) system c) kind-of-quantity and measurement unit d) method e) limitations and interference 6-month QC data collected across routinely encountered events (e.g. calibrator and reagent changes, different operators, equipment maintenance, environmental fluctuations ) Calculate the standard deviation (SD) or coefficient of variation (CV%) Calculate the expanded measurement uncertainty

9 Examples of Measurand Definition

10 Expanded Measurement Uncertainty Confidence level (P) Coverage factor (k) 90 % % 1.96 (~2) 99% 2.58 Expanded Measurement Uncertainty = Uc (CVa) * k Where, k=2 (95 % coverage factor)

11 Equation of Measurement Uncertainty 量測不確定度是個總和概念, 不能與結果值相對應, 與量值 y 對應的是擴充不確定度,kUc(y) Result=y±kUc(y) Where, k=coverage factor

12 Measurement Uncertainty Goal 1) Internationally agreed performance goals (e.g. Cholesterol, HbA 1 C) 2) Acceptable limit based on intra-individual biological variation Optimum CV imp 0.25 CV intra Desirable CV imp 0.50 CV intra Minimum CV imp 0.75 Cv intra Where CV imp = Coefficient of variation derived from intermediate measurement precision (several runs, operators, reagent and calibrator batches) CV intra = Coefficient of variation derived from intra-individual biological variation of the specified measurand

13 Example Cholesterol Mean SD CV Control mg/dl 4.0 mg/dl 2% Control mg/dl 5.0 mg/dl 2% 該實驗室 Cholesterol 之擴充不確定度 (expanded measurement uncertainty) 為 2*CVa=2*2%=4% (k=2) 若某病人生化 Cholesterol 結果為 200 mg/dl, 此數據並不代表病人血中膽固醇就是 200 mg/dl, 而是代表病人血中 Cholesterol 濃度在 200±U 的範圍內的某一點 若檢驗 ( 前 ) 時無作業疏失,±U 即代表量測技術上的測定誤差所導致的變動範圍 U= 測定值 *2CVa, 意即 U=200*2(2%)=8mg/dL, 若檢驗過程無任何錯誤時, 病人血中真正 Cholesterol 為 200±8 (192~208 mg/dl) 的範圍內 (95% CL)

14 NCEP and CLIA Criteria for Lipid and Lipoprotein Testing

15 Clinical Applications Indication of the confidence the lab has that the report is correct. Comparison of results with reference values and previous results. Clinical interpretation and patient management. An essential component of traceability.

16 Clinical Applications Example

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18 References 1. 定量檢驗品管 - 檢驗作業指引 2010 年 台灣醫事檢驗學會 ( 2. Requirements for the estimation of measurement uncertainty National Pathology Accreditation Advisory Council, Australia. 3. Evaluating measurement uncertainty in clinical chemistry Vicki Barwick, LGC. 4. Technical Guide 4: A Guide on Measurement Uncertainty in Medical Testing The Singapore Accreditation Council. 5. Uncertainty of Measurement in Quantitative Medical Testing Australian Association of Clinical Biochemistis.

19 Thank You.