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WS/T 493-2017: Guide to the estimation of the measurement uncertainty of reference methods in enzymology reference laboratiories
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Guide to the estimation of the measurement uncertainty of reference methods in enzymology reference laboratiories
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Basic data | Standard ID | WS/T 493-2017 (WS/T493-2017) | | Description (Translated English) | Guide to the estimation of the measurement uncertainty of reference methods in enzymology reference laboratiories | | Sector / Industry | Health Industry Standard (Recommended) | | Classification of Chinese Standard | C50 | | Word Count Estimation | 42,475 | | Date of Issue | 2017-09-06 | | Date of Implementation | 2018-03-01 | | Regulation (derived from) | State-Health-Communication (2017) 14 | | Issuing agency(ies) | National Health and Family Planning Commission of the People's Republic of China | WS/T 493-2017: Guide to the estimation of the measurement uncertainty of reference methods in enzymology reference laboratiories
---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Guide to the estimation of the measurement uncertainty of reference methods in enzymology reference laboratiories
ICS 11.100C50
People's Republic of China Health Industry Standard
Enzymology reference laboratory reference method measurement uncertainty
Assessment Guidelines
Released on.2017-09-06
Implementation of.2018-03-01
Issued by the National Health and Family Planning Commission of the People's Republic of China
Table of contents
Preface Ⅲ
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Abbreviations 2
5 Measurement uncertainty 2
5.1 Error and uncertainty 2
5.2 Sources of uncertainty 3
5.3 Classification of uncertainty 5
6 Evaluation of measurement uncertainty 6
6.1 General steps for evaluating measurement uncertainty 6
6.2 Process of evaluating measurement uncertainty 6
7 Specific steps to assess measurement uncertainty 7
7.1 Provision to be measured 7
7.2 Measurement procedures and measurement models for the IFCC reference method to measure the concentration of enzyme catalytic activity 9
7.3 Identify all possible sources of measurement uncertainty 12
7.4 Drawing the cause and effect (fishbone) diagram of the measurement process and the uncertainty calculation formula of the whole measurement process 16
7.5 List the value of each input 17
7.6 Calculate the standard uncertainty of each input and draw the estimated table 18
7.7 Calculate the concentration of enzyme catalytic activity (μkat/L) 25
7.8 Evaluation of the uncertainty of the synthetic standard in the whole process of measurement 25
7.9 Calculate the expanded uncertainty (U) and determine the synthesis factor (K) and unit 27
7.10 Contribution graph of input quantity to measurement uncertainty and main input quantity 27
8.Uncertainty report 28
8.1 General 28
8.2 Required information 29
8.3 Reporting standard uncertainty 29
8.4 Report expanded uncertainty 29
8.5 Compliance with limits 29
Appendix A (informative appendix) Finding the source of measurement uncertainty and drawing of causal (fishbone) diagram 31
Appendix B (informative appendix) Common sources and values of uncertainty 36
Appendix C (informative appendix) Data distribution function 38
Foreword
This standard was drafted in accordance with the rules given in GB/T 1.1-2009.
Drafting organizations of this standard. Beijing Hospital, Beijing Aerospace General Hospital, First Affiliated Hospital of Nantong Medical College of Jiangsu Province, Guangdong Provincial Hospital of Traditional Chinese Medicine, Shanghai
Shanghai Municipal Clinical Laboratory Center, Peking Union Medical College Hospital of Chinese Academy of Medical Sciences, Beijing Shijitan Hospital.
The main drafters of this standard. Yang Zhenhua, Chen Baorong, Wang Huimin, Huang Xianzhang, Wang Jing, Ju Yi, Qiu Ling, Zhang Man.
Enzymology reference laboratory reference method measurement uncertainty
Assessment Guidelines
1 scope
This standard specifies the source of measurement uncertainty, the steps for evaluating measurement uncertainty, and the procedures for the evaluation of the
Report method.
This standard applies to the measurement uncertainty of the enzymatic reference laboratory evaluation reference method for measuring the concentration of enzyme catalytic activity, and also applies to the
The measurement uncertainty evaluation of other reference methods measured by the principle of spectrophotometry can also be used by accredited assessors in the assessment process
use.
2 Normative references
The following documents are indispensable for the application of this document. For dated reference documents, only the dated version applies to this article
Pieces. For undated references, the latest version (including all amendments) applies to this document.
JJF1001-2011 General measurement terms and definitions
JJF1059.1-2012 Evaluation and expression of measurement uncertainty
CNAS-GL06..2006 Guidelines for the Evaluation of Uncertainty in Chemical Analysis
3 Terms and definitions
The following terms and definitions defined in JJF1001-2011 apply to this document.
3.1
System formation provides reference.
Example 1.A certain amount of serum derived from a larger amount of serum.
Example 2.An unbiased or randomly selected subgroup of a set of measurement results.
3.2
Verification by checking and providing objective evidence to show that it can meet the specific requirements of the intended application.
Example. The measurement program that is usually used to measure the nitrogen concentration in water is also confirmed to be able to measure the nitrogen concentration in human serum.
Note. The expected application or user needs are outside the measurement system and have nothing to do with it; but the performance is part of the measurement system or measurement program, that is, it
Within the measurement system (verification).
3.3
Through inspection and provide objective evidence to show that a specified item can meet specific requirements.
Example. Demonstrate that the performance of the measurement system or regulatory requirements are met.
Note 1.The prescribed items can be processes, measurement procedures, substances, compounds or measurement systems.
Note 2.The specific requirements can be to meet the manufacturer's technical performance.
Note 3.In chemistry, the verification of the nature or activity of the entity involved requires the description of the structure or characteristics of the entity or activity.
4 Abbreviations
The following abbreviations apply to this document.
5 Measurement uncertainty
5.1 Error and uncertainty
5.1.1 The error is a single value. In principle, the value of the known error can be used to correct the result. The uncertainty is in the form of an interval
It shows that when evaluating an analysis process and the specified sample type, it can be applied to all the measurement values described. For most medical experiments
In terms of testing items in the laboratory, the measurement uncertainty is related to the measurement value. Generally, the uncertainty value cannot be used to correct the measurement result. this
In addition, the difference between error and uncertainty is also reflected in. the revised analysis result may be very close to the measured value, so the error can be
ignore. The uncertainty can be large because the analyst is not sure how close the measurement results are. The uncertainty of the measurement result is not
It can be interpreted as representing the error itself or the residual error after correction.
Note. Error is an ideal concept, it is impossible to know exactly.
5.1.2 It is generally believed that the error contains two components, called random component and systematic component, including the following.
--- Random errors usually result from unpredictable changes in the amount of influence. These random effects make the measured repeated observations
Make a change. Random errors in analysis results cannot be eliminated, but they can usually be reduced by increasing the number of observations;
Note. The arithmetic mean value or the experimental standard deviation of the mean value of a series of observations is a measure of the uncertainty of the mean value produced by some random effects.
Random error that is not the mean. The exact value of the random error of the average value produced by these random effects is unknown.
---Systematic error is defined as the error that remains constant or changes in a predictable way during a large number of analyses of the same measured
Differential component. It is independent of the number of measurements, so it cannot be used by increasing the number of analyses under the same measurement conditions.
It reduces. include.
● Constant system error. For example, reagent blanks are not considered in quantitative analysis, or inaccuracy in calibration of multi-point equipment,
It may be constant at a given measurement value level, but it may also change with the level of different measurement values;
● Unstable systematic error. In a series of analyses, the influencing factors have undergone systematic changes in quantity, such as
Insufficient control of conditions will produce unconstrained systematic errors.
Example 1.During chemical analysis, the temperature of a group of samples is gradually increasing, which may cause gradual changes in the results.
Example 2.During the entire test, the sensors and probes may have aging effects, which may introduce inconstant system errors.
5.1.3 Another form of error is false error or excessive error. This type of error makes the measurement invalid, and it is usually caused by human error or instrumentation.
The generator fails. Digital carry when recording data, bubbles in the flow cell of the spectrometer, or accidental cross-contamination between samples, etc.
Common causes of errors. Include the following.
---False errors are not always obvious. When the number of repeated measurements is large enough, outlier testing should usually be used to check this
Whether there is suspicious data in the group data. All positive results in outlier tests should be treated with care and should be reported to
The experimenter verified. Normally, a certain value cannot be eliminated based on statistical results alone.
---The measurement uncertainty of the error difference is unacceptable, and this type of error cannot be calculated into the measurement uncertainty. However, the factor
Errors caused by word carry can be corrected, especially when this error occurs in the first digit.
5.1.4 All identified significant system effects of the measurement results should be corrected. Measuring instruments and systems usually require measurement standards or
The reference material is adjusted or calibrated to correct the system influence. The uncertainty and correction process related to these measurement standards or reference materials
The uncertainty that exists in it should be considered.
5.1.5 The uncertainty obtained with this document does not consider the possibility of false errors or excessive errors.
5.2 Sources of uncertainty
5.2.1 Common sources
In actual work, the uncertainty of the results may come from many sources, such as incomplete definitions, sampling, matrix effects and interference, environmental regulations
Uncertainty of parts, quality and capacity instruments, reference values, estimations and assumptions in measurement methods and procedures, random changes, etc.
5.2.2 The main source of uncertainty in the enzymatic reference laboratory
5.2.2.1 Pre-measurement stage
5.2.2.2.1.1 Sampling and sample preparation
The main task of the enzymology reference laboratory is to assign values to the commissioned samples, and generally there is no sampling problem. But if you still accept the assessment of sample variability
During work such as variation, sample stability, etc., internal or external sampling is part of the prescribed procedure, such as random changes between different samples.
Influencing factors such as potential deviations in the sampling procedure constitute the uncertainty component that affects the final result. This document will not be
discuss.
Liquid samples often need to be stored at a deep low temperature (such as -70°C) and must be thawed before measurement. The thawing conditions should be strictly controlled and placed in
18℃～20℃ water bath. In addition, it should be mixed after melting, and the mixing method, time and intensity should be strictly controlled to control the uncertainty
source.
The lyophilized powder sample needs to be reconstituted with distilled water before measurement. The quality of the distilled water added should be strictly controlled, and it should be laboratory-grade water. maybe
When possible, the weighing method should be used to control the amount of water added and specify the method of mixing after reconstitution. These measures are used to reduce measurement uncertainty during sample preparation.
Fixed degree.
5.2.2.2.1.2 Storage conditions
If the test sample is to be stored for a period of time before analysis, the storage conditions may affect the results. Therefore, storage time and storage conditions are also
It is considered a source of uncertainty.
Enzymology reference laboratories should note that certain enzymes are denatured by cold rather than heat. Such as cryopreservation of samples, will accelerate the denaturation of lactate dehydrogenase, from
And produce uncertainty.
5.2.2.2.1.3 Influence of the instrument
The following instruments will affect the measurement results of enzyme catalytic activity concentration, including.
---Spectrophotometer. The main sources of uncertainty are wavelength accuracy, half-wave width, accuracy of reading, noise and drift, etc.;
--- Pipette. Maximum allowable error (MPE) and repeatability;
---Balance. Maximum allowable error, etc.
The enzymology reference laboratory should use the most advanced analytical instruments, and check the performance of the instrument before use to ensure that the performance is within the specified parameters.
The uncertainty can be evaluated according to the parameters claimed by the manufacturer.
5.2.2.2.1.4 Reagents
There are many sources of uncertainty in the preparation of enzyme reaction reagents, even if the raw materials of the preparation reagents have been tested, because the detection process exists
Certain uncertainties, such as the inability to know the concentration of the titration solution in some cases. Many organic indicators are not 100% pure and may contain
Isomers and inorganic salts. For the purity of such substances, manufacturers usually only indicate that it is not lower than the specified value. Assumptions about purity levels will
Introduce an uncertainty component.
Changes in the concentration of various components in the reaction mixture may be the source of measurement uncertainty. the speed of the enzymatic reaction is affected by the concentration of various substances.
Effects include substrates, activators, inhibitors, buffers, etc. When the enzyme coupling reaction is used to measure the concentration of enzyme activity, various tool enzymes (referring to
Show enzyme, auxiliary enzyme) and corresponding substrate. The reference method has done research and regulation of the optimum concentration of various substances in the reagent. In the preparation of reagents
At the same time, as long as the advanced balance is used for weighing, the concentration changes are small and often negligible, and their standard uncertainty is not calculated. But note
It is intended to weigh very small hours, such as pyridoxal phosphate in ALT and AST measurement reagents, and 5'AMP in CK measurement reagents. It is best to pass the experiment
Verify that these substances can cause greater measurement uncertainty due to weighing errors.
The aging of the reagents and the preparation of different batch numbers will also cause measurement uncertainty. If the reagents are prepared before each batch measurement, the measurement results
The results include the uncertainty caused by the preparation of reagents and remove the effects of reagent aging.
A small amount of impurities may inhibit or activate the catalytic activity of the enzyme, which may be a very important source of measurement uncertainty. Have
It is necessary to formulate stricter requirements for the raw materials used to prepare enzyme measurement reagents, such as the content of D-alanine in L-alanine and the content of glycine in diglycine.
Quantity and so on.
5.2.2.2.1.5 Principle of measurement-Hypothetical quantitative relationship of chemical reactions
When it is assumed that the analysis process is carried out in accordance with the quantitative relationship of a specific chemical reaction, it may be necessary to consider deviations from the expected chemical reaction definition.
Quantity relationship, or incomplete reaction or side reaction.
5.2.2.2 Measurement phase
5.2.2.2.1 Environmental conditions during measurement
Volumetric glass instruments are generally used at an ambient temperature different from the calibration temperature. The total temperature effect should be corrected, but the liquid and
The uncertainty of the glass temperature should be considered. Similarly, when the material is sensitive to possible changes in humidity, humidity is also important, at this time humidity
The impact should also be corrected.
5.2.2.2.2 Effects of samples
The recovery rate of the analyte in a complex matrix or the response of the instrument may be affected by the matrix composition. The species of the analyte will make this effect
The sound becomes more complicated. The stability of the sample (analyte) may be affected during the analysis process due to changed thermal conditions or photodecomposition.
Health changes. When using "feed samples" to estimate the recovery rate, the recovery rate of the analyte in the sample may be different from the recovery rate of the feed sample.
This introduces uncertainty that needs to be considered.
5.2.2.2.2.3 Blank correction
The value and suitability of blank correction will have uncertainty, which is especially important in trace analysis.
5.2.2.2.2.4 Other important sources of uncertainty
The speed of enzyme-catalyzed reactions is affected by changes in pH. Generally speaking, each enzyme has its optimal reaction pH, and the reaction speed increases with the change in pH.
Rise or fall. This component should be considered when evaluating measurement uncertainty. Different enzymes react inconsistently to pH. When evaluating measurement uncertainty
Always calculate the sensitivity factor.
Multiple chemical substances can often be used to prepare the same pH buffer, and appropriate raw materials should be selected. At this time, not only the pKa of the raw material must be considered
In order to ensure sufficient buffer capacity, it is also necessary to consider whether the raw material itself can inhibit or activate the catalytic activity of the enzyme.
5.2.2.2.4.2 Temperature during enzyme-catalyzed reaction
Temperature has a significant effect on the concentration of enzyme catalytic activity. Generally speaking, an increase in temperature will accelerate the reaction, but after a certain temperature, due to enzyme
The protein denatures and the reaction speed slows down. When evaluating the measurement uncertainty, the sensitivity coefficient of temperature influence is often calculated.
5.2.2.3 Post-measurement stage
The molar extinction coefficient should be used when calculating the enzyme activity concentration, and the uncertainty of this coefficient should be considered. Some instruments use linear regression, press
The calculation result of the slope sometimes leads to a poor fit, so a larger uncertainty is introduced.
Rounding can lead to inaccuracies in the final result, but these are rarely predictable, so it is recommended not to be in the calculation process, but in the calculation process.
Finally, the contract is revised, so it may not be necessary to consider the uncertainty caused by the revision.
5.2.2.4 Other
5.2.2.2.4.1 Influence of laboratory conditions
5.2.2.4.1.1 Temperature and humidity. The temperature and humidity in the laboratory during measurement usually have a certain impact on the measurement, especially for enzymatic measurement, different temperature and humidity
Conditions have different influences on many measurement-related links such as sample addition, heat dissipation of the spectrophotometer, balance weighing, etc., and usually can produce certain
Uncertainty of measurement, but no effective evaluation method has been found yet. Try to keep the temperature and humidity consistent in the laboratory during the measurement is an effective control measurement
The method of uncertainty.
5.2.2.2.4.2 Magnetic field, noise and vibration. As enzymology projects usually use spectrophotometer to measure, strong magnetic field, noise and vibration will interfere with temperature.
For measurement based on electronic signal mode and working principle, the measurement area should be far away from strong magnetic field, noise and vibration area.
5.2.2.2.4.2 Influence of the operator
Regardless of the stage, the operator has a great influence, which may be an important source of measurement uncertainty. To detect and reduce this weight
For measurement uncertainty, operators should be strictly trained and assessed. Different batches are measured by different technicians.
5.2.2.2.4.3 Random influence
There is uncertainty due to random effects in all measurements. When evaluating measurement uncertainty, this item should be regarded as an uncertainty
The source is included in the list.
5.3 Classification of uncertainty
5.3.1 When expressed in standard deviation, the measurement uncertainty component is called the standard measurement uncertainty. If there is a correlation between the components,
Covariance should be considered. The combined effect of several components can be evaluated, which can reduce the total workload of evaluating uncertainty. If the above is combined
The several uncertainty components considered are correlated, and only need to consider the covariance in the synthesis. In the final synthesis, there is no need to consider their relative
Related.
5.3.2 For the measurement result s, its uncertainty is called the composite standard measurement uncertainty, recorded as sc(y), which is an estimated standard deviation,
It is equivalent to using the law of uncertainty propagation to combine all measurement uncertainty components (regardless of how they are evaluated) into the positive square of the overall variance
root.
5.3.3 When reporting measurement results, the extended measurement uncertainty U is often used. The extended uncertainty means that the measured value is
The width of the interval at which a high confidence level exists. U is obtained by multiplying the composite standard uncertainty yc(y) by the inclusion factor Y. Select the inclusion factor K
The time should be based on the required confidence level. For a confidence level of approximately 95%, the value of k is 2.
When reporting the expanded uncertainty, the inclusion factor K should be indicated, because only in this way can the combined standard uncertainty of the measured value be restored to
It is reserved for use when it may be necessary to use this quantity to calculate the combined uncertainty of other measurement results.
6 Evaluation of measurement uncertainty
6.1 General steps for evaluating measurement uncertainty
6.1.1 Step 1.Specify to be measured
Clearly state what needs to be measured, including the measured quantity and the input quantity that is measured (such as the measured quantity, constant, calibration standard value)
Etc.). The technical information related to the measurement shall be given in the description of standard operating procedures (SOP) or other methods.
6.1.2 Step 2.Identify the source of uncertainty (see Appendix A)
List possible sources of uncertainty. Including the uncertainty of the parameters contained in the measurement model relationship specified in the first step
Source, but also consider that there may be other sources. Should include those sources of uncertainty caused by chemical assumptions.
6.1.3 Step 3.Quantification of the uncertainty component (see Appendix A)
Draw a causal (fishbone) diagram and uncertainty calculation formula; list the value and value of each uncertainty source identified and listed in the second step
Calculate the size of the relevant uncertainty component. It is often possible to evaluate or determine the individual components of uncertainty associated with a large number of independent sources. also
It is important to consider whether the data listed reflect all sources of uncertainty. Often need to plan other experiments and research to
Ensure that sources of uncertainty have been fully considered.
6.1.4 Step 4.Calculate the combined uncertainty and expanded uncertainty
The information obtained in the third step is only some quantized components of uncertainty. They may be related to a single source or several
The combined effects of the sources of uncertainty are related. These components should be expressed in the form of standard deviation and in accordance with the relevant rules of the uncertainty propagation law
Perform synthesis to obtain the combined standard uncertainty, and select an appropriate inclusion factor to give the expanded uncertainty.
6.2 The process of evaluating measurement uncertainty
The process of evaluating measurement uncertainty is shown in Figure 1.
Figure 1 The process of evalu...
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