Quality Control Flashcards by Jasela Pabellosa

Ability of a method to measure the smallest concentration of analyte

Sensitivity

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Ability of a method to measure only the analyte of interest

Specificity

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Nearness to the true value

Accuracy

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Determines how much of analyte can be identified in a sample

Recovery study

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Determines a specific compound that affects the lab tests

Interference study

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Used to assess the presence of error im actual patient sample

Sample comparison study

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Repeated results that agree with one another

Precision

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Degree by which a method is easily repeated

Practicablity

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Ability of a method to maintain accuracy and precision over a period of time

Reliability

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Ability of a method to detect the true positive

Diagnostic sensitivity

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Ability of a method to detect the true negative

Diagnostic Specificity

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Involves analyses of control samples together with the patient specimen

Intralab or Internal QC

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Involves proficiency testing programs that periodically provide samples of unknown concentrations to participating laboratories

Interlab or External QC

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Note: some proficiency tests are QUALITATIVE however Chemistry tests should be QUANTITATIVE

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Note:

In external QC, difference of greater than 2SD indicates that the lab is not in control

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Objectives of QC

Stability of machine, reagent and operator

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Note:
Accuracy of any assay depends on the control solutions. Chemistry assay used 2 levels of control solutions while Immunoassay used 3 levels of control solutions

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The different control materials should be analyzed for how many days?

20 days

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For highly precised assays such as blood gases, how many days is the analysis

5 days

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Expected values represented by intervals of acceptable values with upper and lower limit

Control Values

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How are control limits calculated

From the mean and SD

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The ideal control/reference limit

(+/-) 2SD

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Characteristic of ideal QC material

Resembles human sample
Inexpensive and stable for long period of time
No communicable disease
No matrix effect
With known analyte cocentration
Convenient packaging

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Note:
QC materials should be available for 1 year (same lot number)

Bovine QC materials are used but not for immunochem, dye-binding and bilirubin assays

Stabilized frozen controls do not require reconstitution

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Gold standard for external qc testing

CAP Proficiency Testing

Note: Method Evaluation * 40-100 samples should be ran by each method in duplicate on the same day over 8-20 days ideally within 4 hours * If only 40 samples will be measured, daily analysis in duplicate of 2-5 specimens should be followed for atleast 8 days * Most impt. characteristic of method evaluation is to DETERMINE IF THE TOTAL ERROR IS LESS THAN THE ALLOWABLE ERROR

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What are the types of error

Random, systematic, constant, proportional, clerical errors

Error that is due to chance; vary from sample to sample; due to instrument, operator and environmental condotions

Random error

Errors that influences observations consistently in one direction; detected as either positive or negative bias; related to calibration problems, deterioration of reagents etc

Systematic error

Refers to the difference between the target value and the assayed value; dependent on the sample concentration

Constant error

Exists when the difference between the test method and the comparative method values is proportional to the analyte concentration

Proportional / Slope / Percent Error

Highest frequency; occurs with the use of handwritten labels and requests

Clerical error

Note: | First step of method evaluation is the PRECISION STUDY which estimates RANDOM ERROR

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Most error free means of requestinh laboratory tests

Online computer output

Note: Allowable error * is based on the quantity of error that will negatively affect the clinical decisions * the long term precision is sufficient if the total imprecision is less than 1/3 of the allowable error

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It is the measure of central tendency

Mean

Measure of a the dispersion of values from the mean

Most frequently used measure of variation

Index of precision

Coefficient of Variation

Used to compare the means or SD of two groups of data

Inferential statistics

Used to determine whether there is a significant difference between the SD of two groups of data

F Test

Midpoint of distribution

Median

Most frequent observation

Mode

Difference between the highest and lowest score in the data

Range

Difference between the value of a data point and the mean value divided by the group's SD

SD Index

Used to determine whether there is a significant difference between the mean of two groups of data

T-test

It is the system that ensures accuracy and precision in the laboratory

Quality Control System

Describes the distribution of data around the mean

Is used to observe values of control materials over time

QC Chart

It is a population probabilty distribution that is symmetric about the mean; occurs when data elements are centered around the mean with most elements close to the mean

Gaussian curve / Bell-shaped curve

Calculates the difference between QC results and the target means; V-shaped; requires computer implementation

CUSUM

Used to compare results obtained on a high and low control serum from different laboratories; X and Y axis

Youden/Twin plot

Most widely used QC chart in the clinical laboratory

Shewhart Levey-Jennings Chart

Control values that either increase or decrease for six consecutive days

Trend

Control values that distribute themselves on one side of the mean for six consecutive days

Shift

Control values that are far from the main set of values

Outliers

Establish criteria for deciding whether an analytic process is out of control

Multirule

Warning rule

1(2)s

Rejection rule; One control exceeds 3SD; Needs correction

1(3)S

Last 2 controls exceed either mean +/- 2SD

2(2)S

Last or any four consecutive control results exceed either mean +/-1SD

4(1)S

Difference between the highest and lowest control result

R4S

Ten consecutive results are on the same side of the target mean

10x

Acceptable reference limit

+/- 2SD

99% confidence

+/- 3SD

68% confidence

+/- 1SD

95% confidence

+/- 2SD

Is the difference between two consecutive measurements of the same analytes on the same individual

Delta check

Are used to measure systematic errors or inaccuracy caused by substances other than the analyte Ex: hgb, lipids, bilirubin

Interference experiments

Is the concentration range over which the measured concentration is equal tp the actual concentration without modification of the method

Linear range

Absurd value; detect sample contamination or dilution

Physiologic unit

Testing performed outside the confines of central laboratory, usually by non-laboratorian personnel; decentralized testing

Point of care testing

Is a systematic action necessary to provide adequate confidence that the laboratory services will satisfy the given medical needs for patient care

Quality assurance

It shows whether a method can measure all the analyte or just a part of it

Recovery experiment

It is the range of values into which 95% of nondiseased individuals will fall

Reference limit