Method Evaluation and Quality Control Flashcards
Identify source of analytic variability:
(1) experiments must be redone when blackout happens
power surges
Identify source of analytic variability:
(2) temperature and humidity being kept constant as to why specimens and experiments are in a very controlled environment
environmental conditons
Identify source of analytic variability:
(3) presence or absence of staining in 0.1 antibody may be caused by contaminated buffer solution
contamination
Identify source of analytic variability:
(4) the medical technologist used the wrong speciment on the CBC test machine
operator technique
Identify source of analytic variability:
(5) 3 Tesla MRI produces clearer image and abnormalities are detected faster than 0.3 Tesla MRI
Instrument differences
Identify source of analytic variability:
(6) external features causing abnormal findings due to hemolysis, lipemia, serum proteins, specimen sitting too long or not properly centrifuged.
Matrix effects
Identify source of analytic variability:
(7) two operators reading the EEG on different time scale in same instrument, one may look at it differently than the other.
Operator technique
Other sources of analytic variability:
Reagents
Test accessories
An all-inclusive, comprehensive system monitoring the accuracy of test results where all steps before, during and after the testing process are considered which includes pre-analytic, analytic and post-analytic factors
Quality Assurance/Assessment
Essentials for quality assurance
Commitment to quality
facilities, resources, competent staff
reliable procedures, methods, instrumentation
Quality assurance provides what?
a structure for achieving lab and hospital quality goals
These systems monitor the analytical process, detects and minimize errors during analysis thus preventing reporting of erroneous test results
Quality Control
Quality control requires following published rules such as?
Westgard rules (accompanied by Levy-Jennings chart)
Type of QC done daily and serves as establishment of reference ranges and validation of new reagent lot and/or shipment. It is done following instrument repair
Internal
type of QC which involves proficiency testing wherein laboratory testing performances are determined via interlaboratory comparisons
external
It is integrated within routine workload and analyzed by personnel who are running the test. It is an ongoing evaluation of results to correct unacceptable results and assess employee competency
Proficiency testing
Pre-Analytical and Analytical causes of error
samples
operators
reagents (degradation, QC material degrad., calibrator d.)
laboratory environment (atmospheric environment: dust, temp., humidity; utility e.: electircal, H20 quality, pressure)
measuring system (instrument failure: software, optics drift, electronic instability)
Some post-analytical sources of error
incorrect reference values
physician not notified of a panic or critical value
incorrect interpretation of lab results by physician
incorrect data entry of lab results
some errors involved in sample presentation and integrity
integrity: lipemia, hemolysis, interfering substances, clotting factors, incorrect tube
presentation: bubbles and inadequate volume
some errors involved in operator capacity and staffing
capacity: training, competency (wrong use of machines +insufficient reagents)
staffing: short staffing, correct staffing
A statistical analysis of lab test data helps define:
Reference ranges for patients
Acceptable ranges for control specimens
statistical concept wherein all values are symmetrically distributed around the mean and has the characteristic bell-shaped curve. It is also assumed for all quality control statistics
Gaussian/Normal Distribution
What determines accuracy and precision in Gaussian distribution?
accuracy: mean of curve at center of curve
precision: data is grouped together as represented by a well-rounded bell curve
What does a curve signify if its center is off the mean?
Low accuracy due to systematic error
What does a curve signify if it is spread out resulting in a flatter curve?
low precision due to random errors
What is an error?
difference between test and reference method results
type of error which is:
- present in all measurements
- can be either positive or negative
- can be a result of many factors including instrument, operator dependence, reagent and environmental variations
- an imprecision of the test system causing scattered control values around the mean
Random error
What are the causes of random error?
air bubbles in reagent improperly mixed reagents reagent lines, sampling, reagent syringes improperly fitting pipette tips clogged or imprecise pipettor fluctuations in power supply
type of error which:
- influences observation consistently in one direction
- can be further broken down into constant and proportional
- displacement of mean from original value
- predictable and causes shifts or trends in contorl charts
systemic error
What are the causes of systemic error?
- change in reagent or calibrator lot numbers
- wrong calibrator values
- improperly prepared reagents
- deterioration of reagents or calibrators
- inappropriate storage of reagents or calibrators
- variation in sample or reagent volumes due to pipetter misalignments
- variation in temperature or reaction chambers
- deterioration of photometric light source
- variation in procedure between technologists
It is the amount by which an analysis varies from the correct result (ie: expected: 50, result: 47, bias =3)
bias
it is a mathematical expression of a group of data around a mean
standard deviation
It indicates what percentage of the mean is represented by the standard deviation. It is also a reliable means for comparing the precision or SD at different units or concentration levels expressed as %.
coefficient of variation
T or F: the larger the CV, the less reproducible the results are (less values closer to mean)
True
How many levels of control material are used to establish a QC system?
2-3
It is the material or preparation used to monitor the stability of the test system, within predetermined limits
Control
the purpose of establishing a QC system is ??
to verify the analytic measurement range of the instrument for a specific analyte
It is when QC data results are distributed on one side of the mean for 6-7 consecutive days
shift
It is when there is consistent increase or decrease of QC data points over a period of 6-7 days
trend
What is the corrective action for technical errors?
identify error and repeat test
It is the range of analyte values that a method can directly measure on the specimen without any dilution, concentration or other pretreatment
Analytical Measurement Range
It is the range of analyte values that a method can report as a quantitative result, allowing for specimen dilution, concentration, or another pretreatment used to expand the direct AMR
Clinical reportable range
system flag for comparison of individual patient results throughout the day or week with computer detection of changes from earlier individual patienr results and helpful to identify pre-analytic errors
Delta check (see trans)
It is the normal or expected value for patients defined as being within +/- 2SD from the mean (based on local population by lab)
Reference ranges (see factors affecting this)
values that indicate a life-threatening situation for the patient. They require notification of the value to nurse or physician which must read back results to technician
critical values and read back of results (see trans)
