2. QC Flashcards by Samantha Boyer

variable that can assume any value within the range of scores that define the limits of the variable

continuous

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Assume a defined set of integers

discrete

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Values fall into unordered categories or classes

nominal/categorical

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Numbers that are discrete and ordered (ranked)

ordinal data

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Mean, range, variability, and distribution of a data set

descriptive statistics

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Concerned with the relationship among different sets or samples of data

inferential statistics

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The closeness of the agreement between the measured value of an analyte to its “true” value.

accuracy

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procedures used to measure accuracy

Comparison of methods
Testing proficiency samples
Recovery experiments

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calculate system’s bias

known value - result

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describe recovery experiment

small amount of concentrtated analyte is spiked into patient sample
percent recovery is found

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percent recovery

% recovery = (spiked result - baseline result)/analyte added

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A systematic error in a method or error caused by some artifact or idiosyncrasy of the measuring system.

Presence of nonrandom events.

bias

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Ability to produce the same value for replicate measurements of the same sample.

precision

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how to measure precision

Validated by running the same sample multiple times

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Closeness of agreement between results of successive measurements carried out under the same conditions

within-run analysis

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Closeness of agreement between results of measurements performed under changed conditions of measurements

between-run analysis

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normal curve around QC mean reflects that…

most of your results fall around the predictive value, but some do not.

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SD is a measure of…

dispersion

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A range around an experimentally determined statistic that has a known probability of including the true parameter

confidence interval

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A statistical measure of the dispersion of data points around the mean

Reflection of precision
Measure of variability

Coeffecient of variation

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statistical equalizer

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variance =

s^2 = 𝛴(x - mean)^2

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SD to CV

1
2
3

68%
95%
99%

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standard deviation

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Defined to be an observation with a large random error

outlier

examples of random errors

Temperature fluctuations unstable instrumentation changes in reagents variation in manual techniques (pipetting, mixing, timing) operator variations

random error affects... systematic error affects...

precision accuracy

Consistently low or high by the same amount over the entire concentration range

constant systematic error

constant systematic error caused by...

Contaminants in the reagent that affect the results by the same amount in all samples

Consistently low or high by an amount proportional to the concentration of the analyte.

proportional systematic error

proportional systematic error caused by...

Incorrect assignment of the amount of analyte in the calibrator. Side reactions of the analyte

Management philosophy for organizational development and a management process for improving the quality of workmanship

total quality management (TQM)

Purpose is to “substantiate the continued accuracy of the test system throughout the laboratory reportable range of the test results for the test system.”

calibration

Refers to procedures for monitoring and evaluating the quality of the analytical testing process of each method to ensure the accuracy and reliability of patient test results and reports.

quality control

factors to consider when selecting QC materials (5)

- The materials must be stable. - The materials must be available in aliquots or vials. - The materials can be analyzed periodically over a long span of time. - There is little vial-to-vial variation. - The concentration of analyte should be in the normal and abnormal ranges.

3 forms of QC materials

- lyophilized or freeze-dried pooled - frozen pooled - liquid pooled

---------- QC material has target values that are determined by the manufacturer. ----------- QC material has no predetermined target values.

assayed unassayed

Show the difference between the observed values and the expected mean

Levey-Jennings control charts

2 values 4 SDs away (one +, one =)

R4s violation

10 values above or below mean

10x violation

4 values 1SD away

41s violation

3 potential causes of a trend

Reagents begin to deteriorate Light source continually diminishes in luminescent intensity Monochromatic filter becomes delaminated

4 potential causes of a shift

Change in incubation temperature Contamination of reagents Changes in calibrator values Changes in pipette volumes

trend of 7 points

7T violation

advantages of QC computer programs

Real-time review Early detection of Q C problems Documentation of the Q C process

questions to ask when patient results change suspiciously

Does this deviation from normal represent a bias in the assay? Is this shift in assay results for this patient a result of a treatment or procedure? Do these results correlate with other same assay testing? (Glucose: POC, Heme & BB: transfusion, dilution)

steps taken toward QC problem resolution

1. Rerun that same aliquot 2. Pour fresh QC aliquot 3. New vial of QC material 4. Look for obvious problems (Clots, low reagent levels, mechanical faults) 5. Recalibrate 6. Involve QC supervisor, and/or instrument support.

AMR is taken over the...

range of linearity

axes for finding linearity/AMR

Concentrations of analytes on x-axis instrument response on y-axis

Range of analyte concentrations that can be directly measured without dilution, concentration, or other pretreatment.

analytical measurement range (AMR)

Range of analyte concentration that can be released after performing dilutions, concentrations, or other pretreatments.

clinical reportable range (CRR)

This range includes all the data points that define the range of observations for a healthy population.

reference range (RR) therapeutic range for drugs

laboratory results that may represent serious conditions relative to the patient.

critical range (CR)

valid CR results need to be...

relayed to the licensed care provider and documented. MD, RN, etc. NOT secretary or unit clerk. First name, last name, credentials Your First name, last name, date, time.

criteria that divide individuals for reference studies into groups

partitioning criteria

Include factors that affect the reference individual, specimen collection, and specimen handling

preanalytical variables

if reference study data does not form a normal distribution...

you must use nonparametric methods, which make no specific assumptions concerning the mathematical form of the probability distribution represented by the observed reference values.

CLSI guidelines for reference studies

A minimum of 120 reference values be used Reference interval be determined by the nonparametric method

Procedure in which two consecutive laboratory results on a patient are compared. If the difference between the two values exceeds a predetermined value (per institution), then the result is flagged.

Delta checks

Verification and release of patient results using software-based algorithms with decision-making logic via the Laboratory Information System (L I S)

autoverification

An example of external quality control wherein an agency or organization provides biological samples whose concentrations are unknown to the testing clinical laboratory.

proficiency testing