QUALITY ASSURANCE and QUALITY CONTROL Flashcards by Janus Palermo

Process by which lab ensures quality results by closely monitoring preanalytical, analytical, & post analytical stages of testing

QUALITY ASSURANCE

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Examples of Preanalytical phase; everything that precedes test performance:

Test ordering
Patient preparation
Patient ID
Specimen collection
Specimen transport
Specimen processing

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Examples of Analytical phase; everything related to assay:

Test analysis
Quality control (QC)
Reagents
Calibration
Preventive maintenance (involves machines)

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Examples of Postanalytical phase; everything that comes after test analysis:

Verification of calculations & preference ranges
Review of results
Notification of critical values
Result reporting
Test interpretation by physician
Follow-up patient care
Delta check

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Part of analytical phase of quality assurance; process of monitoring results from control samples to verify accuracy of patient results

Quality Control (QC)

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It is the average of data points:

Mean

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It is the midpoint of distribution

Median

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It is the most frequent observation

Mode

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It is the difference between highest and lowest value; easiest measure of spread

Range

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Most frequently used measure if variation:

Standard Deviation (SD)

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An index of precision used to compare the dispersion of two or more groups of data with different units/concentrations

Coefficient of variation (CV)

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Used to determine if there is a significant difference between the means of two groups of data; compares accuracy

T-test

mnemonic: “ATM”
A - Accuracy
T - T-test
M - Mean

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Used to determine if there is a significant difference between the SD of two groups of data; compares precision:

F-test

mnemonic: “SPF”
S - SD
P - Precision
F - F-test

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____% of the data fall between +/- SD from the mean

68%

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_____% of the data fall between +/-2 SDs from the mean.

95%

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_____% of the data fall between +/-3 SDs from the mean

99%

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Relationship of SD with Dispersion:

Directly proportional

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Relationship of SD with Precision:

Inversely proportional

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Nearness or closeness of assayed values to the true value:

Accuracy

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Nearness or closeness of assayed valued to each other

Precision (Reproducibility)

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Ability of an analytical method to maintain accuracy and precision over an extended period of time

Reliability

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Degree by which a method can easily be repeated

Practicability

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Ability to measure the smallest concentration of the analyte of interest

Analytical sensitivity

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Ability to measure only the analyte of interest

Analytical specificity

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Also known as linearity; range of values over which lab can verify accuracy of test system

Reportable range

Formerly call 'normal value'; can vary for different patient populations.

Reference interval

Reference interval is established by testing minimum of ____ healthy subjects & determining range in which 95% fall

120 healthy subjects

Verifying reference interval includes how many study subjects/individuals?

as few as 20 study individuals (as few as 40 study individuals) - Bishop 8th edition

Reporting a positive result in a patient who has the disease

True Positive (TP)

Reporting a positive result in a patient who doesn't have the disease

False Positive (FP)

Reporting a negative result in a patient who doesn't have the disease

True negative

Reporting a negative result in a patient who has the disease

False negative

% of population with the disease that test positive; ability of the analytical method to detect the proportion of individuals with the disease

Diagnostic Sensitivity

Formula of Dx. Sensitivity:

Dx. Sensi = TP / (TP + FN) x 100

% of population without the disease that test negative; ability of the analytical method to detect the proportion of individuals without the disease

Diagnostic Specificity

Formula of Dx. Specificity:

Dx. Speci = TN / (TN + FN) x 100

Important in "ruling out" the disease and selecting screening test:

Diagnostic Sensitivity

Important in "ruling in" the disease and for confirmatory test:

Diagnostic Specificity

% of time that a positive result is correct; Totality positive result

Positive Predictive Value (PPV)

Formula for PPV:

PPV = TP / (TP + FP) x 100

% of time that a negative result is correct; Totality of negative result

Negative Predictive Value (NPV)

Formula for NPV:

NPV = TN / (TN + FN) x 100

Assayed on a regular schedule to verify that a laboratory procedure is performing correctly:

QC samples

For new instrument or new lot of reagents, analyze QC materials for ____ days

20 days Note: also make new LJ chart for new reagent/instrument

Characteristics of ideal QC materials:

1. Must resemble human samples 2. Inexpensive and stable for long periods 3. No communicable disease 4. No known matrix effects 5. With known analyte concentrations (for assayed controls) 6. Convenient packaging for easy dispensing and storage

Most common presentation for evaluating QC results; shows each QC result sequentially over time; also called a Shewart plot

The Levey-Jennings Control Chart

When are you going to stop plotting in the LJ chart?

Once there is a new reagent or instrument.

Errors observed on LJ charts:

Trend Shift Outliers

LJ chart error where control values are increasing or decreasing for six consecutive runs

Trend

Main cause of trend error:

Deterioration of reagents

LJ chart error where six consecutive values are on the same side of the mean

Shift

Main cause of shift error:

Improper calibration of instrument

Highly deviating values; control result outside established limits:

Outliers

1 control >+/- 2s from mean. warning flag of possible change in accuracy or precision

1 (2s)

1 control >+/- 3s from mean

1 (3s)

2 consecutive controls >2s from mean on same side

2 (2s)

2 consecutive controls differ by >4s

R (4s)

4 consecutive controls >1s from mean on same side

4 (1s)

10 consecutive controls on same side of mean

10x

Example of Westgard rules that are random errors:

1(2s) 1(3s) R(4s)

Example of Westgard rules that are systematic errors:

2(2s) 4(1s) 10x

Type of error that is present in all measurements; due to chance; no means of predicting it; error that doesn't recur in regular pattern:

Random error

Error that influences ALL observations consistently in one direction; recurring error inherent in test procedure;

Systematic error

Examples of Random errors:

- Error due to dirty glassware - Use of wrong pipet - Voltage fluctuation - Sampling error - Anticoagulant or drug interference

Examples of Systematic errors:

- Dirty photometer - Faulty ISE - Evaporation or contamination of standards or reagents

Also known as external quality assessment; consists of evaluation of method performance by comparison of results versus those of other laboratories for the same set of samples:

Proficiency testing

Components of a QA program:

- Patient identification - Collection of samples - Testing - Delta checks - Critical values/Panic values - Data reporting - Preventive maintenance

Comparison of patient data with previous results:

Delta checks

Failed delta check deviation:

>20% deviation

QUALITY ASSURANCE and QUALITY CONTROL Flashcards

(69 cards)