Hematology Test 1 Chapter 2

What does the diagnostic specificity of a test for a given disease represent?

Proportion without the disease who have a negative test result.

The tubing that brings the lyse reagent to the hemoglobin cuvette on an automated cell counter is pinched and not delivering any reagent. All hemoglobin values are greater than 20 g/dL. This represents what type of error?

Constant systematic

How are Westgard rules used to interpret control data?

"Westgard rules" are generally used with 2 or 4 control measurements per run, which means they are appropriate when two different control materials are measured 1 or 2 times per material, which is the case in many chemistry applications.

What is a one-tailed test?

.If the sample has one (high or low) values.

A patient's white blood cells (WBCs) are counted on an automated cell counter 10 times. The mean white count is 8000/mL, and the standard deviation (SD) is 300. What is the coefficient of variation (CV)?

3.8% % CV = (SD/mean) × 100 = (300/8000) × 100 = 3.8%

Which is true regarding reference ranges?

Are ranges of values for an analyte in normal healthy people

Laboratory certification is available from what agency?

Board of Certification of the American Society for Clinical Pathology.

What is the formula for the coefficent of variation (CV%)?

CV=(SD)x100/mean

What is a delta check?

Comparison of current results of a lab test with previous results for the same test on the same patient.

What dispersal limits are established for control results?

Control results must fall within predetermined dispersion limits, typically +SD.

List the agencies that address hematology and hemostasis quality.

Data Innovation North America Clinical and Laboratory Standards Institute Centers for Medicare and Medicaid Services American Proficiency Institute College of American Pathologists The Joint Commission Laboratory Medicine Quality Improvement/

What is a constant systematic error ( or bias, in laboratory vernacular)?

Is a constant difference between the new and reference assay regardless of assay magnitude.

What is a primary standard?

Is a material of known,fixed composition that is prepared in pure form, often by determining its dry mass on an analytical balance.

What is the definition for analytical specificity?

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

A laboratory gets numerous complaints regarding the length of time it takes hematology results to get to the emergency department. What would be an appropriate response?

Make this a quality assurance project.

What is the common term for low-end assay interference?

Noise

List some examples of postanalytical quality efforts?

Publication of reports, timeliness, and patient satisfaction.

What is QA?

Quality Assurance- is the broader concept, encompassing pre-analytical, analytical, and postanalytical variables.

List some examples of preanalytical quality efforts?

Test orders, test request forms, stat orders and timeliness, specimen collection, specimen transport, and specimen management.

A clinical laboratory scientist performs 30 replicate hemoglobin determinations on a single blood sample. When statistics are used to determine the precision of the method, the mean is 13.8 g/dL and 1 SD is 0.1 g/dL. This means that 95.5% of the results on this specimen lie:

between 13.6 and 14.0 g/dL.

A purchased hemoglobin standard is used to adjust a hemoglobinometer. This standard is being used as a:

calibrator.

Define variance

expresses the deviation of each data point from its expected value.

A laboratory comparing its results to those of other laboratories on the same specimen is an example of:

external quality assessment.

The best way to prevent errors in the laboratory is to:

hire professionals with integrity.

What is accuracy?

how close a measurement is to the true value; implies freedom from error

A patient specimen is analyzed on an instrument known to be in control from previous assays performed on a calibrated instrument and gives a hemoglobin result of 13.2 g/dL. Two hours later it is evaluated on another instrument that is being evaluated for purchase by the laboratory. The result is 11.8 g/dL. This result, when compared with the first, is:

inaccurate.

Define median

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

Proper specimen collection and patient satisfaction are components of:

quality assurance.

A test that is positive in all patients who have the disease but also in some who do not have the disease is:

sensitive

The control values for both controls for the prothrombin test were ranging between the mean and ±1 SD for the first 19 days of use. Starting on day 20, the values for both were consistently between +1 and +2 SDs. This is an example of a:

shift.

What is a null hypothesis?

states that there is no difference among the groups being compared.

The precision limits of a method are defined by:

the SD.

Define mean

the average value in a data set it is determined by adding all the values & dividing the sum by the # of values in the set.

State the conventional levels for significance (rejecting the null hypothesis).

0.05 (5%) or 0.01 (1%).

State the acceptable SD limits for establishing biologic reference intervals (normal ranges).

95% of observations are x+ 2.0 SD from the mean

What is alternative hypothesis?

Research hypothesis (there IS a relationship between variables)

What is the student's t-test?

The student's t-test compares the mean of a data set(sample) of a new or modified assay to the sample mean of a reference assay.

How are control results plotted?

They are plotted on a Levey-Jennings chart that displays each data point compared with the mean and limits .

What is the value of the Levy-Jennings chart?

They are useful to identify problems relating to shifts, trends, and dispersion.

When can a new lot be rejected?

They can be rejected when more than one specimen data point pair generates a variance greater than 10% or when all variances are positive or negative.

According to the US Food and Drug Administration, what are the categories of assays?

They categorizes assays as approved, cleared, modified cleared, analyte- specific reagent (ASR), research use only (RUO), and laboratory-developed tests ( "home-brew").

What steps should be taken on a patient sample that has results above the linear limit?

They must diluted and reassayed. Results from the diluted specimens that fall within the linear range are valid; however, they must be multiplied by the dilution factor to produce the final concentration.

What is the minimum number of samples used in establishing a reference interval by the process of transference?

They only need to assay 30 specimens, approximately 15 males, and 15 females.

How is the median value of a sample set identified?

To find the median, the data should be arranged in order from least to greatest. If there is an even number of items in the data set, then the median is found by taking the mean (average) of the two middlemost numbers.

What is a calibration?

Use of standards (calibrators) establishes reference points for analyzers to measure at specified concentrations. Sets the relationship between concentration of an analyte and instrument's "signal".

Define mode

value that occurs most often

What is variance?

variance expresses the deviation of each data point from its expected value.

What is the definition of ROC?

A ROC curve is 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 continuous variable.

What are the forms of continuing education for the laboratorian?

Associate degree (2-year) or medical laboratory tech. Bachelor degree (4-year) or medical laboratory-Scientist. Master's degree or professional Doctorate in Clinical Laboratory Science (DCLS).

How is ANOVA different from a T-Test?

An ANOVA test can be applied to more than two sets of data.

What is the difference between the diagnostic sensitivity and the analytical sensitivity of a laboratory method?

Analytical sensitivity represents the smallest amount of substance in a sample that can accurately be measured by an assay. ... "Diagnostic sensitivity" is the percentage of persons who have a given disorder who are identified by the assay as positive for the disorder.

Under what testing circumstances is it extremely important to use an assay that has a very high diagnostic sensitivity?

Assays that possess high sensitivity and low specificity make effective screening tests.

Under what testing circumstances is it extremely important to use an assay that has a very high diagnostic specificity test?

Assays with high specificity provide effective confirmation when used in follow-up to positive results on screening assays.

What is the educational difference between a clinical laboratory tech. and the clinical laboratory scientist

Associate degree (2-year) or medical laboratory tech. Bachelor degree (4-year) or medical laboratory-Scientist.

What is the Bland-Altman Difference Plot used for?

Bland-Altman plots are extensively used to evaluate the agreement among two different instruments or two measurements techniques. Bland-Altman plots allow identification of any systematic difference between the measurements (i.e., fixed bias)

What is the moving average concept?

Dr. Brian Bull proposed a method of employing patient RBC indices to monitor the stability of automated blood cell analyzers, recognizing that the RBC indices, mean cell volume (MCV), mean cell hemoglobin (MCH), and hemoglobin concentration (MCHC) remain constant on average despite individual patient variations.

What are the Westgard rules?

Dr. James Westgard has established a series of internal QC rules that are routinely applied to long term- deviations.

Why are lot-to-lot reagent comparisons performed?

Each change in reagent lots can adversely affect the consistency and quality of patient results. Good laboratory practice requires evaluation of each new reagent lot prior to use.

What is system-wide comparability?

Each site validates its instrument-reagent systems, perhaps relaying on central laboratory support. Subsequently, the system is validated as a whole.

What are the components of assay feasibility?

Feasibility studies include a review of assay throughput (number of assays per unit time), dwell time ( length of assay interval from specimen sampling to report), cost per test, cost/benefit ratio, turnaround time, and the technical skill required to perform assay.

How are calibrators prepared and used in the clinical laboratory?

Follow the instrument or reagent manufacturer's instructions for calibration. If not available, choose a frequency that is dictated by your internal QC frequency. Assess the required frequency of calibration when validating assays. Depending on the stability of the assay it may be necessary to recalibrate more/less frequently. Re-calibrate every time a reagent batch is changed, unless you can demonstrate that changing reagent lot numbers does not adversely affect control values and patient results. Re-calibrate when your QC results are showing a systematic bias - calibration can eliminate trends or small analytical bias. Re-calibrate after major instrument maintenance, such as lamp changes, which can cause shifts in QC values.

What is the definition of accuracy?

How closely a measured value is to an accepted value (target)

What is a two-tailed test?

If the sample has two (high and low) values.

What is linearity?

Is the ability to generate results proportional to the calculated concentration or activity of the analyte?

What issues should be considered in the evaluation of a new test or instrument?

Issues of operator safety, footprint, overhead, compatibility with laboratory utilities and information system, the need for middleware, frequency and duration of breakdowns, and distributor support and service.

What slope and intercept are generated in a perfect correlation regression analysis?

It generates a slope of 1 and a y intercept 0.

What is the formula by which a positive predictive value is derived? And what does it predict?

It is derived from a true positive and false positive. It predicts the probability that an individual with a positive assay result has the condition or disease.

What is the formula by which a negative predictive value is derived? What does it predict?

It is derived from true negative and false-negative tests. It predicts the probability that an individual with a negative assay result does not have the disease or condition.

When is re-calibration necessary?

It is necessary whenever reagent lots are updated unless the laboratory professional that the reportable range is unchanged using lot-to-lot comparison.

What is the use of proficiency systems in the clinical laboratory?

Laboratory managers and directors assess and document professional staff skills using proficiency systems. They may be also used to assess applicants for laboratory positions.

Why do laboratories participate in proficency systems?

Many state health agencies provide proficiency testing surveys, requiring laboratories to participate as a condition of licensure.

How is variance calculated?

Measures the extent to which values in a data set vary -subtract each individual value from the mean for the group -Square each result -Add results -Divide the sum of the squares by the number of values minus one to get an average of the squared variations from the mean

What procedures are included in a validation study?

Method validation includes proof of accuracy; precision; reportable ranges, including the analytical measurement range (AMR); and detection of interfering substances.

What does the p scale represent?

Power is expressed as P, which stands for the probability that the test is able to detect an effect.

In which situation is quality control material acceptable?

QC material is only acceptable if all the site's reagents and QC materials share the same lot number, which may not apply if the coagulometers are different.

What is QC?

Quality Control processes are employed to document assay validity, accuracy, and precision, including external quality assessment, publication of reference intervals and therapeutic ranges (when applicable), and lot-to-lot validation.

What are reference intervals used for?

Range of test results for a given analyte that is seen in healthy population of individuals.

What steps can be performed in the laboratory to ensure continued reliability of the assay?

Regularly scheduled validity rechecks, lot-to-lot comparisons, instrument preventive maintenance, staff competence, and scheduled performance of internal QC and external quality assessment procedures.

What is precision?

Reproducibility: Closeness of the observations to each other. Implies freedom from variation.

One of two controls that have been evaluated over the last 28 days gives a result on day 29 between 2 and 3 SDs of the mean; the other control is within 2 SDs of its mean. What is the correct procedure to follow?

Rerun the control and, if acceptable, continue with patients.

What is the formula that is used to calculate diagnostic sensitivity test?

Sensitivity (%) = TP/(TP + FN) x 100

What does the diagnostic sensitivity of a test for a given disease represent?

Sensitivity refers to a test's ability to designate an individual with disease as positive. A highly sensitive test means that there are few false negative results, and thus fewer cases of disease are missed. The specificity of a test is its ability to designate an individual who does not have a disease as negative.

How does a secondary standard differ from a primary standard?

So basically, secondary standard serves the purpose of external quality control for smaller labs. This makes it essential that the secondary standard must first be standardized against the primary standard. standard solution one must use aquous solution of high grade purity.

What is the formula for a Diagnostic specificity test?

Specificity(%)= TN/ (TN+FP) x 100

What are controls?

Specimens similar to blood or plasma with known values. Used to monitor QC. Treated as a patient specimen. Should produce results with the pre-established range.

What are two keys to assay reliability?

Staff integrity and professional staff competence.

The antinuclear antibody (ANA) test is positive in almost all people who have systemic lupus erythematosus (SLE). It is also positive in some patients who do not have SLE. The antideoxyribonucleic acid (anti-DNA) test is positive only in people with SLE but not in all who do. Which of the following is true?

The ANA test is a good screening test, and anti-DNA test is a good confirmatory test.

What two hematology and coagulation assays are used to monitor the therapeutic range?

The INR for prothrombin time is used to monitor the effects of oral warfarin (Coumadin) therapy. The therapeutic range for monitoring treatment with unfractionated heparin using the PTT assay must be established locally by graphically compring the regression of the PTT results in seconds agaist the results of the chromogenicanti-Xa heparin assay.

What are proficiency or survey testing samples?

The aliquots are often called survey or proficiency testing specimens. They include preserved human subject plasma and whole blood, stained peripheral blood films, and bone marrow smears, and photomicrographs of cells or tissues.

What does the central laboratory do to reduce confusion generated from multiple reference intervals

The central laboratory may develop and publish a system-wide RI from individual facility intervals, presuming the individual RIs are similar.

What are delta checks?

The current analyte result is compared with the result for the same analyte from the previous specimen from the same patient.

What is mode?

The data point that appears most often?

What is the proportional systemic error?

The highest the analyte value, the greater the deviation from the line of identity. Proportional errors are caused by malfunctioning instrument components or a failure of some part of the testing process.

Explain the development of a local laboratory's adult reference interval.

The laboratory professional carefully defines the desired healthy population and recruits reprensentative subjects who meet the criteria to provide blood specimens.

When a laboratory is establishing a completely new reference interval for an analyte, what is the most important characteristic within the reference sample group?

The laboratory professional carefully defines the desired healthy population and recruits representative subjects who meet the criteria to provide blood specimens. The chosen healthy subjects should match the institutions population demographic in terms of race and age.

What threshold is selected when performing ROCs?

The limit is finally selected is the one that provides the largest true-positive and the smallest false-positive rate.

What confidence interval is used for most reference ranges established by clinical laboratories?

The limits at mean +2 SDs encompass 95.46% of results from healthy individuals, known as the 95.5% confidence interval.

What is the p scale range?

The power of a statistical test is defined as its ability to reject the null hypothesis when the null hypothesis is false.

What is the range of Pearson r (correlation coefficient)?

The range is from -1.0 to +1.0.

What happens to an assay run when a control is outside the control limits?

When a value falls outside of these limits the analysis should stop,patient results held, and the test system investigated. Reviewing the pattern of points plotted over time is useful in spotting shifts and trends in method calibration.

What is the difference between within-a-day precision and day-to-day precision?

Within-Run" precision is the result of running the same sample several times in the same run. "Day-to-Day" precision is evaluated as the facility utilizes an analyzer over multiple days.

What is the formula to calculate the mean?

You add the sum of all data points than you divide by the number of data points.

What is the standard deviation (SD)?

a commonly used measure of dispersion, is the square root of the variance and is the mean distance of all the data points sample from the sample mean.

How do accuracy and precision differ?

accuracy describes the difference between the measurement and the part's actual value, while precision describes the variation you see when you measure the same part repeatedly with the same device.