CH. 2 - Quality Assurance

Quality

Implies the ability to provide accurate, reproducible assay results that offer clinically useful information

Reliability

This requires vigilance and effort on the part of all laboratory professionals

Quality Assurance

• Defined as "part of quality management focused on providing confidence that quality requirements will be fulfilled.”

• This is the broader concept, encompassing pre-analytical, analytical, and post-analytical variables.

Pre-pre

Laboratory assay utilization and physician test ordering patterns

Post-post

Analytical variables, and the appropriate application of laboratory assay results

Null hypothesis

It states that there is no difference between or among the means or variances of the populations being compared

Alternative (research) hypothesis

It is the logical opposite of the null hypothesis

Power (P)

• Defined as its ability to reject the null hypothesis when the null hypothesis is false.

• Determined by the sample size (number of data points, n), the design of the research study, and the study’s ability to control for extraneous variables

Mean

It is a standard expression of central tendency employed in most scientific applications

Median

• It is the data point that separates the upper half from the lower half of a data set.

• It is a robust expression of central tendency in a skewed distribution because it minimizes the effects of outliers

Mode

• It is the data point that appears most often in the sample

• It is NOT a true measure of central tendency

Variance (σ2)

It expresses the deviation of each data point from its expected value, usually the mean of the data set (sample) from which the data point is drawn

Standard deviation (SD)

• It is a commonly used measure of dispersion

• This is the square root of the variance and is the mean distance of all the data points in a sample from the sample mean

Coefficient of variation (CV)

• It is the normalized expression of the SD, ordinarily articulated as a percentage.

• It is also the most commonly used measure of dispersion in laboratory medicine.

Accuracy

Measure of agreement between an assay value and the theoretical “true value” of its analyte

Precision

It is established by using repeated within-day, and day-to-day assays, then computing the mean, standard deviation (SD), and coefficient of variation (CV) of the results

Linearity

It is the ability to generate results proportional to the calculated concentration or activity of the analyte

Analytical Sensitivity (LLOD)

These assays are coupled with linearity and AMR studies

Analytical Specificity

It is the ability of an assay to distinguish the analyte of interest from anticipated interfering substances within the specimen matrix.

6

The recalibration interval may be once every __ months.

Recalibration

This is necessary whenever reagent lots are updated.

Once

In the lab, the controls should be run at least ______ per shift.

Levey-Jennings Chart

It assumes that the control results distribute in a Gaussian manner and imprint limits at 1, 2, and 3 SD above and below the mean

Dr. James Westgard

He established a series of internal QC rules that are routinely applied to long term deviations, called the Westgard rules

(δ) Delta-check system

It compares a current analyte result with the result from the most recent previous analysis for the same patient

External Quality Assessment

It validates the accuracy of hematology and hemostasis assays by comparing results from identical aliquots of specimens distributed at regular intervals among laboratories nationwide or worldwide

• Preserved human subject plasma and whole blood

• Stained peripheral blood films

• Bone marrow smears

• Photomicrographs of cells or tissues

Examples of survey or proficiency testing specimens:

Diagnostic efficacy testing

It includes determination of diagnostic sensitivity and specificity, positive and negative predictive value, and receiver operating characteristic (ROC) analysis

False positives

Results are generated from non-disease specimens

False negatives

Results are generated from specimens taken from patients with proven disease

Prevalence

• The total number of events or conditions in a broadly defined population.

• Quantitates the burden of disease on society but is not qualified by time intervals and does not predict disease risk

Incidence

• The number of events occurring within a randomly selected number of subjects representing a population, over a defined time.

• Numbers are non-cumulative.

ROC curve

A further refinement of diagnostic efficacy testing that may be employed to determine the decision limit (cutoff, threshold) for an assay when the assay generates a continuous variable.

Dr. Brian Bull

He proposed a method of employing patient RBC indices to monitor the stability of automated blood cell analyzers

Screening test

It is an assay that is applied to a large number of subjects within a convenience sample where the participant’s condition is unknown

Proficiency testing

All conscientious laboratory directors subscribe to an external quality assessment system, also known as?

Moving average algorithm

GUIDE QUESTION:

What procedure is NOT employed to validate a new assay?

Constant systematic error

GUIDE QUESTION:

You validate a new assay using linear regression to compare assay calibrator results with the distributor’s published calibrator results. The slope is 0.99 and the y intercept is 110%. What type of error is present?

Student t-test

GUIDE QUESTION:

Which is a statistical test that compares means?

Precise but not accurate

GUIDE QUESTION:

The acceptable hemoglobin control value range is 13 6 0.4 g/dL. The control is assayed five times and produces the following five results: 12.0 g/dL 12.3 g/dL 12.0 g/dL 12.2 g/dL 12.1 g/dL

These results are:

5400 to 6600/mL

GUIDE QUESTION:

A WBC count control has a mean value of 6000/mL and an SD of 300/mL. What is the 95.5% confidence interval?

Analytical specificity

GUIDE QUESTION:

The ability of an assay to distinguish the targeted analyte from interfering substances within the specimen matrix is called:

Laboratory-developed test

GUIDE QUESTION:

The laboratory purchases reagents from a manufacturer and develops an assay using a protocol published in a volume of the Methods in Molecular Biology series. How would the FDA classify this assay?

Distribution of proficiency materials to all sites

GUIDE QUESTION:

What process ensures comparability in multi-site validation?

Establishing the RI by transference

GUIDE QUESTION:

A laboratory scientist measures prothrombin time for plasma aliquots from 15 healthy men and 15 healthy women. She computes the mean and 95.5% confidence interval and notes that they duplicate the manufacturer’s statistics within 5%. This procedure is known as:

Control

GUIDE QUESTION:

You purchase a preserved whole blood specimen from a distributor who provides the mean values for several complete blood count analytes. What is this specimen called?

College of American Pathologists (CAP)

GUIDE QUESTION:

What agency provides external quality assurance (proficiency) surveys and laboratory accreditation?

American Society for Clinical Laboratory Science (ASCLS)

GUIDE QUESTION:

What agency provides continuing medical laboratory education?

Preanalytical quality assurance

GUIDE QUESTION:

Regular review of blood specimen collection quality is an example of:

Postanalytical quality assurance

GUIDE QUESTION:

Review of laboratory report integrity is an example of:

Area under the curve

GUIDE QUESTION:

When performing a receiver operating curve analysis, what parameter assesses the overall efficacy of an assay?

Proficiency testing

GUIDE QUESTION:

You require your laboratory staff to annually perform manual lupus anticoagulant profiles on a set of plasmas with known values. This exercise is known as: