QUALITY ASSURANCE IN THE CLINICAL CHEMISTRY LABORATORY

Quality Control (QC)

It involves the process of monitoring the characteristics of the analytical processes and detects analytical errors during testing, and ultimately prevent the reporting of inaccurate patient test results.

It is one component of the quality assurance system, and is part of the performance monitoring that occurs after a test has been established.

It is a system ensuring accuracy and precision in the laboratory by including quality control reagents in every series of measurements.

Standard
Control
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Quality Control Reagents:

Sensitivity

It is the ability of an analytical method to measure the smallest concentration of the analyte of interest.

Specificity

It is the ability of an analytical method to
measure only the analyte of interest.

Accuracy

It is the nearness or closeness of the assayed
value to the true or target value.

recovery,
interference and
patient sample comparison.

Accuracy is estimated using 3
types of studies:

Recovery study

determines how much of the analyte can be identified in the sample.

Interference study

determines if specific compounds affect the laboratory tests like hemolysis, turbidity and icteric.

Sample comparison study

is used to assess presence of error (inaccuracy) in
actual patient sample.

Reproducibility

Precision is also known as

Precision

It is the ability of an analytical method to give repeated results on the same sample that agree with
one another.

Practicability

It is the degree by which a method is easily repeated.

Reliability

It is the ability of an analytical method to maintain accuracy and precision over an extended period of time during which equipment, reagents and personnel may change.

Diagnostic Sensitivity

It is the ability of the analytical method to detect the proportion of individuals with the disease.

More true (+) and Less False (-)

Screening tests require high sensitivity so that no case is missed.

Diagnostic Specificity

It is the ability of analytical method to detect the proportion of individuals without the disease.

More True (-) and less False (+)

Confirmatory tests require high specificity to be certain of the diagnosis.

Intra-lab Quality Control (Internal QC)

It involves the analyses of control samples together with the patient specimens.

It detects changes in performance between the present operation and the "stable" operation.

Inter-lab Quality Control (External QC)

It involves proficiency testing programs that periodically provides samples of unknown concentrations to participating clinical laboratories.

It is also used to determine state-of-the-art interlaboratory performance.

The College of American Pathologists (CAP) proficiency program is the gold standard for clinical laboratory external QC testing.

ensure our clinicians that patient results are accurate.

The ultimate goal of proficiency testing is to

2 Controls (Normal, and Abnormal)

General Chemistry:

(Low, Normal, and Abnormal)

Immunoassay:

20 days (all level of controls)

New instrument

20 days (all level of controls)

New lot numbers

5 days

Highly precise assays (with CV less than 1%) such as blood gases

Matrix effects

are results of improper product manufacturing, use of unpurified human and nonhuman analyte additives and altered protein components.

40 to 100, 8 to 20 days, 4 hours

It is recommended by Westgard et al and Clinical Laboratory Improvement Amendments (CLIA) that _________ samples be run by each method in duplicate
on the same day over _________ , ideally within ______, to determine its accuracy and precision.

precision study

The first step in method evaluation is the _______ which estimates the random error.

(mmol/L) or percentages

It is determined for each test method and is expressed either in measurement units of the analyte

VARIATIONS

Are errors encountered in the collection, preparation and measurement of samples, including transcription and releasing of laboratory results.

Random Error

It is present in all measurements; it is due to chance.

It is a type of error which varies from sample to sample.

It is the basis of varying differences between repeated measurements -variations in technique.

Systematic Error

It is an error that influences observations consistently in one direction (constant difference).

It is a measure of the agreement between the measured quantity and the true value.

It is detected either positive or negative bias.

Constant Error

It refers to a difference between the target value and the assayed value.

It is independent of sample concentration.

It exists when there is a continual difference between the comparative method and the test method regardless of the concentration.

Proportional /Slope/Percent Error

It results in greater deviation from the target value due to higher sample concentration.

It exists when the difference between the test method and the comparative method values is proportional to the analyte concentration.

handwritten labels and request forms.

highest frequency of clerical errors occurs with the use of

29%

Nonlaboratory personnel were responsible for ____ of the errors with regard to laboratory results.

Online computer input

most error-free means of requesting laboratory tests.

preanalytical and postanalytical stages

Most laboratory errors occur in the

STATISTICS

It is the science of gathering, analyzing, interpreting and presenting data.

Inferential Statistics

are used to compare the means or standard deviations of two groups of data

F-test

is used to determine whether there is a statistically significant difference between the standard
deviations of two groups of data

Median

is the value of the observation that divides the observations into two groups, each containing
equal number of observations. It is the midpoint of a distribution; 50th centile

Mode

is the most frequent observation; it is used to describe data with two centers (bimodal).

Range

is the simplest expression of spread or distribution; it is the difference between the highest and lowest score in a data

Standard Deviation Index (SDI)

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

t-test

is used to determine whether there is a statistically significant difference between the means of two groups of data

Mean

Is a measure of central tendency. It is associated with symmetrical or normal distribution.

Standard Deviation (SD)

Is a measure of the dispersion of values from the mean. It helps describe the normal curve. A measure of the distribution range.
It is the most frequently used measure of variation.
describes the distribution of all values around the mean.

Coefficient of Variation (CV)

Is a percentile expression of the mean; an index of precision.
allows a laboratorian to compare SDs with different units.

Variance

Is called the standard deviation squared; a measure of variability. It represents the difference between each value and the average of the data.

SD and variance represent the average distance from the center of the data (mean) and every value in the data set.

95%

The acceptance range is ____ confidence limit which is equivalent to ±

QUALITY CONTROL CHART

It is used to observe values of control materials over time to determine reliability of the analytical method.

It is utilized to observe and detect analytic errors such as inaccuracy and imprecision.

Gaussian Curve (Bell-Shaped Curve)

It occurs when the data set can be accurately described by the SD and the mean.

It is obtained by plotting the values from multiple analyses of a sample.

It focuses on the distribution of errors from the analytical method rather than the values from a healthy or patient population.

Cumulative Sum Graph (CUSUM)

It calculates the difference between QC results and the target means

Common method: V-mask

It identifies consistent bias problems; it requires computer implementation.

Youden/Twin Plot

It is used to compare results obtained on a high and low control serum from the different laboratories.

proportional error

The points falling from a center but on the 45˚ line suggest a

constant error

points falling from the center but not on the 45˚ line suggest a

Shewhart Levey-Jennings Chart

It is the most widely used QC chart in the clinical laboratory.

It allows the laboratorians to apply multiple rules without the aid of a computer.

It is a graphic representation of the acceptable limits of variation in the results of an analytical method.

It easily identifies random and systematic errors.

Trend

It is formed by control values that either increase or decrease for six consecutive days.

Deterioration of reagents

Main cause of trend

Shift

It is formed by control values that distribute themselves on one side or either side of the mean for six consecutive days.

improper calibration of the instrument

Main cause of shift

Outliers

These are control values that are far from the main set of values

These are highly deviating values.

These are caused by random or systematic errors.

Westgard Control Chart

It recognizes that the use of simple upper and lower control limits is not enough to identify analytical problems.

control rule

Westgard used the term _______ to indicate if the analytical process is out of control.

potential problem.

A control value between 2s and 3s is a sign of a

corrective action.

A control value outside the 3s would require

2s , 3s

Some laboratories use the ____ as a warning limit and the ____ as an error limit.

Six Sigma

It is a performance improvement program.

It is a tool that can be used to reduce laboratory errors, increase productivity and improve quality in the clinical laboratory.

To reduce the number of defects to near zero.

Main goal of six sigma

Defects

anything that does not meet customer requirements

Lean System

It is a system for reducing waste ("non valued activities") especially in production or manufacturing processes.

It was conceptualized to improve the automobile industry in terms of the quality and efficiency of automobile production.

Analytical Run

It is a set of control and patient specimens assayed, evaluated and reported together.

Delta Check

It is the most commonly used patient based-QC technique.

It requires computerization of test data so that current results can be compared with past results.

It is the difference between the two consecutive measurements of the same analytes on the same individual.

Interference experiments

These are used to measure systematic errors or inaccuracy caused by substances other than the analyte.

Interferences: hemoglobin, lipids, bilirubin, anticoagulants and preservatives

Linear Range/Dynamic Range

It is the concentration range over which the measured concentration is equal to the actual concentration without modification of the method.

Physiologic Limit

Is sometimes referred to as absurd value.

It helps detect sample concentration or dilution, inadequate sample volume, inadequate reagent
volumes, sudden major problems with the method, or incorrect recording or transmission of the result.

Point of Care Testing (POCT)/Decentralized Testing

It is a type of analytical testing performed outside the confines of the central laboratory, usually by non-laboratorian personnel (nurses, respiratory therapists, etc).

Most commonly used POCT: use of portable whole blood glucose meters for the management of patients with diabetes mellitus.

To deliver quality services and products to customers.

Primary Goal of QA:

Quality Assurance (QA)

It can be envisioned as a tripod with program development, assessment and monitoring, and quality improvement forming the three legs.

Quality Patient Care

It includes effective test request forms, clear instruction for patient preparation and specimen handling, appropriate turn-around time for specimen processing, testing and result reporting, appropriate reference ranges and intelligent result reports.

Recovery experiment

It shows whether a method measures all the analytes or only part of it.

It estimates inaccuracy or systematic error.

Predictive value

It depends on sensitivity, specificity, and prevalence of the disease being test.

When a test cutoff changes, its accuracy (sensitivity/specificity) and predictive value also change.

Bayes' theorem (predictive value theory) describes the relationship between posttest and pretest probability of disease or no disease based on the sensitivity and specificity of the test.

Positive predictive value

It is the probability that a positive test indicates disease;
it is the proportion of persons with a positive test who truly have the disease.

Negative predictive value

It is the probability that a negative test indicates absence of disease. It is the proportion of persons with a negative test who are truly without disease.

Reference Limit/Reference Interval/Reference Value

It is a value obtained by observation or measurement of a particular type of quantity on a reference individual.

It is the range of values into which 95% of non diseased individuals will fall - this definition implies that 5% of non diseased individuals can have laboratory results outside the reference range.

It is the usual values for a healthy population that represents 95% central tendency.