QUALITY ASSURANCE/CONTROL Flashcards by LYNMIL MORENO

Overall program that ensures that the final
results reported by the laboratory are correct

Quality Assurance

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➔ AKA External Quality Control
➔ Involves proficiency testing
programs
➔ Ex.: National External Quality
Assessment Scheme (NEQAS)

Interlab

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➔ System of ensuring accuracy and precision in the lab
➔ Process of ensuring that analytical results are correct
➔ QC samples are measured periodically in the same manner as clinical samples

Quality Control

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➔ AKA Internal Quality Control
➔ Analyses of control samples
together with patient specimens
➔ Important in daily monitoring

Intralab

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Reagent without any analyte added

Reagent Blank

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➔ Most specific analytical solution
➔ Value will tell the conc. of the
unknown
➔ Only one analyte

Standard

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➔ Value will determine accuracy and
precision
➔ Resembles patient sample
➔ Many analyte

Control

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Indicating a person has the disease when, in fact, he or she does not

False positive

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-Done on apparently healthy
individuals
-Not a basis for treatment
-Less accurate, less expensive

Screening Test

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-Done on sick or ill individuals
-Basis for treatment
-More accurate, more expensive

Diagnostic Test

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Refers to how well the test measures what it is
supposed to measure. It refers to the accuracy of the test, meaning how close the result is to its true value.

Validity

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Indicating a person has the disease when, in fact, he or she does

True positive
(TP)

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Refers to how well the test performs in use over time.
It refers to the precision of the test, meaning how close are the results of a test on repetition or how close the
values are from one another.

Reliability

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Indicating a person has the disease when, in fact, he or she
does not

False positive
(FP)

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Indicating a person does not have the disease when, in fact, he or she
does

False negative
(FN)

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Ability of test to detect the smallest amount of
analyte

SENSITIVITY

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Indicating a person does not have
the disease when, in fact, he or she
does not

True negative
(TN)

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Ability of test to identify correctly those who
have the disease (a) from all individuals with
the disease (a+c)

Diagnostic Sensitivity

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Ability of the test to identify correctly those
who do not have the disease (d) from all
individuals free from the disease (b+d)

Diagnostic Specificity

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Diagnostic Sensitivity formula

TPTP + FN

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Ability of test to detect substances without
interferences

SPECIFICITY

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Diagnostic Specificity formula

TNTN + FP

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Measure of central
tendency

Mean

Middle value

Median

Most frequent value

Mode

Highest value – lowest value

Range

Measures of dispersion

Standard Deviation and Variance

Predictable errors; an error that is constant when measurements are made under the same conditions Causes: deterioration of reagents, improperly made standard solutions, contaminated solutions, calibration problems, failing instrumentation

SYSTEMATIC ERRORS

Index of precision

Coefficient of Variation

Unpredictable errors; often due to instrument, operator, and environmental conditions ➔ Causes: pipetting error, mislabeling of samples, temperature fluctuation, improper mixing of sample and reagent

RANDOM ERRORS

-is the most commonly used histogram in QC ➔ A histogram is/are sheets of rectangular coordinate graphing paper where data for sequential analysis are plotted to locate the source of error

LEVEY-JENNINGS CHART

SYSTEMATIC ERRORS Two types:

Constant error & Proportional error

is a “multi-rule” system ➔ Developed by Dr. James O. Westgard ➔ Based on statistical concepts which is a combination of decision criteria or rules to assess if a system is in control

Wesguard Multirule System

Violated if the IQC value exceeds the mean by ±2SD

12SD

Violated if four consecutive IQC values exceed the same limit (mean ± 1SD)

41SD

Violated when the IQC value exceeds the mean by ±3SD

13SD

Violated when two consecutive IQC values exceed the mean on the same side of the mean by ±2SD

22SD

Violated when one control exceeding the +2s and another exceeding the -2s

R4SD

➔ AKA Linear or Dynamic Range ➔ Range of analyte concentrations that can be directly measured without dilution, concentration, or other pretreatment

Analytic Measurement Range (AMR)

Violated when 10 consecutive IQC values are on the same side of the mean or target value

10x

How close the measured value is to the true value due to systematic error, which can be either constant or proportional

Accuracy

Ability of a method to detect small quantities or small changes in concentrations of an analyte

Analytic Sensitivity

➔ Difference between the true value and the measured value

Bias

➔ AKA Cross-reactivity ➔ Ability of a method to detect only the analyte it is designed to determine

Analytic Specificity

➔ Type of systematic error in the sample direction and magnitude; the magnitude of change is constant and not dependent on the amount of analyte

Constant Error

➔ Effect of a compound/s on the accuracy of the detection of a particular analyte

Interference

➔ Substances that cause interference

Interferents

➔ Lowest amount of analyte accurately detected by a method

Limit of Detection

➔ Lowest amount of analyte that can be reported while achieving a precision target (e.g. lowest concentration at which a CV of 10% may be achieved)

Limit of Quantitation

➔ Type of systematic error where the magnitude changes as a percent of the analyte present, error dependent on analyte concentrations

Proportional Error

➔ Error varies from sample to sample ➔ Causes include instrument instability, temperature variations, reagent variation, handling techniques, and operator variables

Random Error

➔ Body component (e.g. fluid and urine) in which the analyte is to be measure

Matrix

➔ Dispersion of repeated measurements about the mean due to analytic error

Precision

➔ Error always in one direction (may be constant or proportional

Systematic Error

➔ Ability of an analytic test to measure a known amount of analyte ◆ A known amount of analyte is added to real sample matrices

Recovery

➔ Random error + Systematic error

Total Error

➔ Refers to the difference between the measured value and the mean expressed as a number of SDs ➔ An SDI = 0: value is accurate or in 100% agreement ➔ An SDI = 3: 3 SDs away from the target (mean) and indicates inaccuracy ➔ SDI may be positive or negative

Standard Deviation Index