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analyte1) The substance to be measured. CLSI recommends using the term “measurand” “for a particular quantity subject to measurement.”
2) a substance measured in the laboratory. a chemical for which a sample (such as water, air, or blood) is tested in a laboratory. for example, if the analyte is mercury, the laboratory test will determine the amount of mercury in the sample.
analytical quality assurance (aqa)Used with charts of operating specifications (OPSpecs charts) to indicate the level of assurance for detecting critical sized errors. For example, 90% AQA(SE) means there will be at least a 90% chance of detecting the critical systematic error when operating within the allowed limits for imprecision and inaccuracy for the given control rules and total number of control measurements (N).
analytical quality requirementUsed here to refer to a quality requirement in the form of an allowable total error (TEa). Often defined on the basis of proficiency testing criteria for acceptable performance, such as the CLIA requirements for regulated analytes.
analytical runGenerally defined by CLIA as an 8 hour to 24 hour interval during which control materials must be analyzed. According to CLSI C24, a run is “an interval (i.e., a period of time or series of measurements) within which the accuracy and precision of the measuring system is expected to be stable. In laboratory operations, control samples are analyzed during each analytical run to evaluate method performance, therefore the analytical run defines the interval (period of time or number of specimens) between evaluations of control results. Between quality control evaluations, events may occur causing the measurement process to be susceptible to variations that are important to detect.”
application characteristicsRefer to those properties of a method which determine whether the method can be implemented in the particular laboratory of interest, assuming the method will perform acceptably. Characteristics such as cost, sample size, specimen type, etc.
assayed control materialA control solution or control material for
biasmeasUsed here to represent the bias of a measurement procedure relative to a comparative method or a comparative group in proficiency testing.
bland-altman plotThe display of paired-data from a comparison of methods experiment by plotting the differences between the test and comparative results on the y-axis versus the average of the test and comparative results on the x-axis. Similar to a traditional “difference plot”, except that the average of the test and comparative results provides the x-value rather than the value of the comparative result alone.
centers for disease control
clinical laboratory improvement amendments of 1988
combined standard uncertaintyStandard uncertainty of the result of a measurement when that result is obtained from the values of a number of other quantities, equal to the positive square root of a sum of terms, the terms being the variances or covariances of these other quantities weighted according to how the measurement result varies with changes in these quantities. [ISO]
control chart"A graphical method for evaluating whether a process is or is not in a `state of statistical control.` The determinations are made through comparison of the values of some statistical measure(s) for an ordered series of samples, or subgroups, with control limits" [ASQ]. In healthcare laboratories, the Levey-Jennings chart is commonly used to plot the result observed for a stable control material versus time, usually the day or run number.
control ruleA decision criterion for interpreting control data and making a judgement on the control status of an analytical run. Symbolized here by AL, where A is the abbreviation for a particular statistic or states the number of control measurements, and L is the control limit. An analytical run is rejected when the control measurements fulfill the stated conditions, i.e., when a certain statistic or number of control measurements exceeds the specified control limits.
criteria for acceptabilityCLIA`s term for the decision criteria applied to assess the validity of an analytical run. Another name for QC procedure, with emphasis on definition of the decision criteria or control rules for interpreting control measurements.
critical-error graphA power function graph on which is imposed the critical-error that needs to be detected. Facilitates the estimation and comparison of the probability for error detection by different QC procedures.
crrchurchill research range
clinically reportable range
cumulative control limitsControl limits calculated from estimates of the mean and standard deviation that represent a time period longer than a month. Common practice is for laboratories to calculate monthly control statistics. Cumulative statistics can be easily calculated from monthly statistics that tabulate the sum of the individual values and the sum of the squares of those values. See the lesson QC - The Calculations for more detailed discussion, equations, and examples.
decision level for critical interpretation (xc)See medical decision level.
deming regressionAn alternate regression calculation that can be employed when ordinary linear regression may not be reliable. This technique takes into account the imprecision of both the test and comparative methods. When the analytical range of comparison results is narrow, ordinary linear regression may give a slope that is too low and a y-intercept that is too high. The correlation coefficient is used as a practical measure of when alternate regression techniques should be applied. When r is less than 0.99 or 0.975, depending on the source of the recommendation, Deming regression or Passing-Bablock regression should be used instead of ordinary linear regression.
examination procedureSet of operations having the objective of determining the value or characteristics of a property. [ISO]
expanded uncertaintyQuantity defining an interval about the result of a measurement that may be expected to encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand.
fda1) functional demonstration and acceptance
2) abbreviation for food and drug administration. organization responsible for, among other things, laser safety.
gaussian curve gaussian distribution normal curve normal distributionRefers to a symmetrical bell-shaped distribution whose shape is given by a specific equation (called the normal equation) in which the mean and standard deviation are variables. It is commonly assumed that the random error of an analytical method fits the Gaussian distribution and therefore can be characterized by calculating the standard deviation. The standard deviation is not a valid statistic if a distribution is not Gaussian.
interference experimentA method validation experiment which estimates the systematic error resulting from interference and lack of specificity. One test sample is prepared by adding the suspected interferer to a sample containing the analyte of interest. A second aliquot of the original sample is diluted by the same amount, then both samples are analyzed by the test method. The average difference of replicate measurements and the average difference for a group of interference samples provide an estimate of constant systematic error.
joint commission for accreditation of healthcare organizations
laboratory accreditation program
levey-jennings control chartA commonly used control chart in which individual control measurements are plotted directly on a control chart with limit lines drawn either as mean ± 2s or mean ± 3s. Time is displayed on the x-axis usually in terms of days or runs.
limit of blank (lob)Highest measurement result that is likely to be observed (with a stated probability) for a blank sample; typically estimated as a 95% one-sided confidence limit by the mean value of the blank plus 1.65 times the SD of the blank. [CLSI]
lot number“An alphanumeric and/or symbolic identification placed on the label by the manufacturer that enables the manufacturing history of the product to be traced.” [CLSI]
method developmentRefers to the process of formulating the materials, conditions, and protocol for measuring an analyte. Method development is mainly carried out by industry. Laboratories may make minor modifications to methods to improve performance, in which case, the modified methods should be subject to more rigorous testing and evaluation by the laboratory.
methodology characteristicsThose properties of a method which in principle should contribute to the best analytical performance in the measurement of the analyte of interest. Characteristics such as the specificity of the chemical reaction, optimization of the reaction conditions, etc.
multi-rule quality-control procedureA control procedure that uses two or more control rules for testing control measurements and determining control status. At least one rule is chosen for its ability to detect random errors and one to detect systematic errors.
non-waived testsUsed in the Final CLIA Rule as a category of tests that encompasses both moderate complexity and high complexity tests. QC regulations in the Final CLIA Rule are the same for all non-waived tests, whereas earlier drafts provided different QC requirements for the classes of moderate and highly complex tests.
operating specifications (opspecs)Used here to describe the imprecision and inaccuracy that are allowable and the QC that is necessary to assure, at a stated level, that a defined quality requirement will be achieved in routine operation.
outliersDiscrepant values. Values which do not agree with the pattern of the majority of other values. They may be due to mistakes or they may represent a significant finding. When outliers are suspected, it is best to calculate the data set with and without the outlier values. If their presence changes the conclusion drawn from the data, then the experimental results are not reliable. It is possible to apply a wide variety of statistical tests or rules for purposes of rejecting outliers, however, the choice of rules is always subject to argument. It is always better to inspect the data as it is collected during the experiment, identify discrepant values, and determine their cause.
passing-bablock regressionAn alternate regression calculation that can be employed when ordinary linear regression may not be reliable. This technique is non-parametric and therefore makes fewer assumptions about the nature of the data. It depends on calculating the slopes of all possible pairs of points, ranking those slopes, and selecting a median value. The correlation coefficient is used as a practical measure of when alternate regression techniques should be applied. When r is less than 0.99 or 0.975, depending on the source of the recommendation, Deming regression or Passing- Bablock regression should be used instead of ordinary linear regression.
performance characteristic“A property of a test that is used to describe its quality.” [CLSI] For a measurement procedure, the performance characteristics include reportable range, imprecision, inaccuracy or bias, interference, recovery, detection limit, and reference interval. Those properties that describe how well a procedure performs. For a control procedure, the performance characteristics are the probabilities for error detection and false rejection, or the average run lengths for rejectable and acceptable quality. For a measurement procedure, the performance characteristics include analytical range, precision, accuracy, interference, recovery, and also the frequency and duration of analytical errors.
physician office laboratory
provider performed microscopy
primary standard material"Substance of known chemical composition and sufficient purity to be used in preparing a primary standard solution" [IFCC].
primary standard solution"Solution used as calibration standard in which the concentration is determined solely by dissolving a weighed amount of primary standard material in an appropriate solvent, and making a stated volume or weight" [IFCC].
process capabilityAn industrial term used to describe how the inherent variability of a production process under stable operation compared to the allowable variation. SEcrit is an index of process capability for an analytical testing process.
process stabilityUsed here to characterize the performance of the measurement procedure in terms of the frequency of analytic runs having medically important errors (f) that invalidate the medical usefulness.
proficiency sample“A specimen containing analytes of unknown concentration or identification that is sent to laboratories participating in testing programs in order to independently verify the laboratory technical competency.” [CLSI]
proficiency testing
qc acceptability criteriaThe term used by CLIA to indicate the decision criteria or control rules used to monitor test performance during a run of patient specimens.
quality assessmentCLIA’s term for the overall system for assuring the quality of laboratory test results. Includes the monitoring and assessment of general laboratory systems, as well as pre-analytic, analytic, and post-analytic systems, with the objective of identifying problems, making corrections, and improving the quality of testing services.
quality managementAll activities of the overall management function that determine quality policy objectives and responsibilities; and implement them by means such as quality planning, quality processes, quality control, quality assessment, and quality improvement within the quality system. [CLSI, ISO]
reference interval experimentA method evaluation experiment in which specimens are collected from selected individuals in defined states of health in order to characterize the expected range of test values for that population.
reference valuesAll of the values observed for a particular determination when sampling a population of individuals in defined states of health.
regression statisticsUsed here to refer to the terms that are commonly calculated, i.e., the slope, y-intercept, and standard deviation about the regression line.
replication experimentA method validation experiment that estimates the random analytical error. It is performed by making measurements on a series of aliquots of a test solution within a specified time period, usually within the time of an analytical run (within-run imprecision), within a day (within-day imprecision), and over a period of at least 20 days (day-to-day or total imprecision).
reportable rangeThe range of concentration of the substance in the specimen for which method performance is reliable and test results can be reported.
six sigmaA concept for world-class quality and a goal for process performance that requires 6 SDs of process variation to fit within the tolerance limit or quality requirement of a process. Applied in the Method Decision Chart as a criterion that requires bias + 6 SDs to be less than TEa, the allowable total error for the test.
state operations manual
statistical control limitsAs used with Levey-Jennings and Westgard multirule types of QC procedures, these are the lines drawn on control charts to define the range of results expected due to the random error of the method. The limits are often obtained from a group of 20 or more measurements on a particular control material by calculating the mean and standard deviation, then using multiples such as the mean plus/minus 3s, 2s, or 1s to establish rejection limits for different control rules.
total error
allowable total error
total error requirementSee allowable total error.
total qc strategyThe balance of the efforts expended on statistical QC, preventive maintenance, instrument function checks, method performance tests, and quality improvement.
true valueGenerally used to indicate that this is the correct analytical concentration or result.
t-testOften called Student’s t-test. A statistical test of significance in which the difference between two mean values is tested. The null hypothesis is that there is no difference between the two means. The test is carried out by calculating a t-value, then comparing the calculated t-value with a critical t-value which is obtained from a statistics table. If the calculated t-value is greater than the critical t-value, the null hypothesis is rejected; this means that a statistically significant or real difference exists between the mean values being compared. If the calculated t-value is less than the critical t-value, the null hypothesis stands, therefore no difference has been observed between the two mean values.
within-run imprecisionThe random error observable within the time period of a single analytical run.