Method Evaluation & Quality Control Flashcards
is used to verify the acceptability of new
methods prior to reporting patient results.
method evaluation
The foundation for monitoring performance (known
as QC)
descriptive statistics
The three most commonly used descriptions of the center of a data set
Mean, median, mode
There are four commonly used descriptions of
spread:
Range, SD, CV, SDI
the most frequently used
measure of variation.
SD
represent the “average” distance from the center of the
data (the mean) and every value in the data set.
CV
a calculation to show the number of SDs a value is from the target mean.
SDI
Three
factors are generated in a linear regression
Slope, y-intercept, correlation coefficient (r)
is a measure of the strength of the
relationship between the two methods.
correlation coefficient (r)
indicates that both variables increase and
decrease together,
positive r
indicates that as one variable increases,
the other decreases.
negative r
An r value of ___ indicates no relationship,
0
r = ___
indicates a perfect relationship.
1.0
An alternate approach to visualizing paired data is the difference plot, which
is also known as the:
Bland-Altman plot
The difference between test and reference method results is called
error
is present in all measurements and can be either
positive or negative, typically a combination of both positive and negative errors
on both sides of the assigned target value.
Random error
influences observations consistently in one direction
higher or lower
Systematic error
exists when there is a
continual difference between the test method and the comparative method
values, regardless of the concentration.
Constant systematic error
exists when the differences between the test
method and the comparative method values are proportional to the analyte
concentration.
Proportional error
TRUE/FALSE: The CLIA final rule requires
that waived tests simply follow the manufacturer’s instructions.
TRUE
Systematic error can be due to constant or proportional error and is estimated
from three types of study:
recovery, interference, and COM
Ability of a method to detect small quantities or
small changes in concentration of an analyte.
Analytic sensitivity
Ability of a method to detect only the analyte it is
designed to determine, also known as cross-reactivity.
Analytic specificity
Also known as linear or dynamic
range. Range of analyte concentrations that can be directly measured
without dilution, concentration, or other pretreatment.
AMR (analytic measurement range)
Range of analyte that a method can
quantitatively report, allowing for dilution, concentration, or other
pretreatment used to extend AMR.
CRR (clinically reportable range)
Method evaluation begins with a _____
precision study
Ability of an analytic test to measure a known amount of
analyte; a known amount of analyte is added to real sample matrices.
Recovery
Effect of (a) compound(s) on the accuracy of detection of a particular analyte.
Interference
Body component (e.g., fluid and urine) in which the analyte is to be measured.
Matrix
The purpose of this type of study is
to determine how much of the analyte can be detected (recovered) in the
presence of all the other compounds in the matrix.
Recovery studies
examines patient samples by the method being
evaluated (test method) with a reference method.
COM studies
designed to determine if specific compounds affect the
accuracy of laboratory tests.
Interference studies
A nonparametric regression method for
comparison studies. It is a robust method that is resistant to outliers.
Passing-Bablok regression
Linear regression analysis (orthogonal least
squares) used to compare two methodologies using the best fit line
through the data points
Deming regression
Defines the strength of relationship
between two variables.
Correlation Coefficient (r)
Indicates the proportion of
variation explained by one variable to predict another.
Coefficient of Determination (r2 or R2)
determined for each test based on the amount of error that will not negatively
affect clinical decisions.
Allowable error
in the laboratory involves the systematic monitoring of analytic processes to
detect analytic errors that occur during analysis and to ultimately prevent the
reporting of incorrect patient test results.
Quality Control
Threshold at which the value is statistically unlikely.
Control limits
Material analyzed only for QC purposes.
Control material
QC
for general chemistry assays generally uses ____ levels of control, while
immunoassays commonly use ____.
two;three
TRUE/FALSE: The underlying
rationale for running repeated assays is to detect random errors that affect
precision.
TRUE
With a new instrument or with new lots of control material, the different levels
of control material must be analyzed for ____ DAYS
20
are
the criteria used to decide that a given method meets the clinical
requirements.
QC specifications
“voice of the customer”
“the
performance the health care provider needs”
QC specifications
“voice of the process”
“natural
variation of a given test”
QC limits
A pair of medical decision points that span the
limits of results expected for a defined healthy population.
Reference interval
Subject preparation, prescription medications, collection time, sample storage, stress, food/beverage ingestion
Preanalytic factors
Precision, accuracy, lot to lot reagents, linearity, interference, recovery
Analytic factors
Statistical test that makes no specific
assumption about the distribution of data.
Nonparametric method
Statistical test that assumes the observed values, or
some mathematical transformation of those values, follow a (normal)
Gaussian distribution
Parametric method
To establish a reference interval, it is recommended that the study includes at
least ____ individuals.
120
- Changes in reagent formulations by the vendor
- Minor changes in reagents due to lot to lot variations
- Differences between reference interval & test popuations-selection bias
Common Problems Encountered when Monitoring
Reference Intervals
Ability of a test to detect a given disease or
condition.
Diagnostic sensitivity
Ability of a test to correctly identify the absence
of a given disease or condition.
Diagnostic specificity
Chance of an individual having a given
disease or condition if the test is abnormal.
Positive predictive value
Chance an individual does not have a given
disease or condition if the test is within the reference interval.
Negative predictive value
To define an appropriate cutoff, laboratorians often use a graphical tool
called the:
receiver operator characteristic (ROC)
can be used to determine the most efficient cutoff for
a test and are an excellent tool for comparing two different tests.
ROC curves
