2. QC Flashcards
variable that can assume any value within the range of scores that define the limits of the variable
continuous
Assume a defined set of integers
discrete
Values fall into unordered categories or classes
nominal/categorical
Numbers that are discrete and ordered (ranked)
ordinal data
Mean, range, variability, and distribution of a data set
descriptive statistics
Concerned with the relationship among different sets or samples of data
inferential statistics
The closeness of the agreement between the measured value of an analyte to its “true” value.
accuracy
procedures used to measure accuracy
Comparison of methods
Testing proficiency samples
Recovery experiments
calculate system’s bias
known value - result
describe recovery experiment
small amount of concentrtated analyte is spiked into patient sample
percent recovery is found
percent recovery
% recovery = (spiked result - baseline result)/analyte added
A systematic error in a method or error caused by some artifact or idiosyncrasy of the measuring system.
Presence of nonrandom events.
bias
Ability to produce the same value for replicate measurements of the same sample.
precision
how to measure precision
Validated by running the same sample multiple times
Closeness of agreement between results of successive measurements carried out under the same conditions
within-run analysis
Closeness of agreement between results of measurements performed under changed conditions of measurements
between-run analysis
normal curve around QC mean reflects that…
most of your results fall around the predictive value, but some do not.
SD is a measure of…
dispersion
A range around an experimentally determined statistic that has a known probability of including the true parameter
confidence interval
A statistical measure of the dispersion of data points around the mean
Reflection of precision
Measure of variability
Coeffecient of variation
statistical equalizer
CV
variance =
s^2 = 𝛴(x - mean)^2
SD to CV
1
2
3
68%
95%
99%
standard deviation
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
- Rerun that same aliquot
- Pour fresh QC aliquot
- New vial of QC material
- Look for obvious problems (Clots, low reagent levels, mechanical faults)
- Recalibrate
- 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
