Calibration and Quality Control Flashcards
what is accuracy?
closeness to the true value
what is precision?
closeness of values to each other
what is traceability?
an unbroken chain of comparisons of measurements leading to a reference value
what makes a good method?
- the right patient
- right time (clinically relevant)
- right tests (appropriate)
- right results (accurate + precise)
what 3 things lead to a good analytical method?
- definitive method
- reference method
- routine method
why is a definitive method important for a good analytical method?
Exceptional scientific accuracy, suitable for certification of reference material
why is a reference method important for a good analytical method?
Demonstrates small inaccuracies against definitive method
why is a routine method important for a good analytical method?
Sufficiently accurate for routine use against reference method and standard reference material (SRM)
what 3 things make a good calibrator?
- primary standard
- standard refernce material (SRM)
- secondary standard
what is the importance of a primary standard to ensure a good calibration?
- A substance of known chemical composition and high purity
- Can be accurately quantified and used for assigning values to materials and calibrating apparatus
what is the importance of a standard reference material (SRM) to ensure a good calibration?
Reference material issued by an institute whose values are certified by a reference method which establishes traceability
what is the importance of a secondary standard to ensure a good calibration?
A commercially produced standard for routine use calibrated against a primary standard or reference material
what is calibration in practical terms?
“resets” an analyser/test
what does calibration ensure?
- Ensures the measured signal is proportional to the concentration of the analyte
- Results from the local analyser match those from a defined reference method
how is calibration achieved in practical terms
- Measure a series of calibrators of known value
- Generate a relationship between assay/instrument output and analyte concentration
- Use relationship to determine the values of unknown samples
what are the types of calibration?
- single point
- multi point
what is a single point calibration?
A calibration method where only one reference point on a measurement scale is used to adjust the accuracy of a device
what is multi point calibration?
a method of calibrating a measuring instrument by using multiple reference points across its operational range
when chosing the type of calibration needed what should you consider?
- Simplicity/complexity
- Cost
- Time
- Accuracy
- Frequency
what is quality control?
Real time monitoring that the assay is performing within pre-set criteria
how is quality control ensured?
Assurance that results are comparable to previous (yesterday/last week/month/year/etc)
what quality controls are in place in practice?
internal quality controls (IQC)
what 3 things are used in interal quality control?
- set of commercially available material
- one or multiple analytes
- various concentrations across the analytical range
what are 2 examples of setting acceptance criteria?
- manufacturer defined target range (usually very wide)
- laboratories usually define their own targets (narrow for accuracy)
how can you briefly summerise the standard deviation equation?
“Sum of the mean” divided by “mean of the sum”
what percentage is 1SD away from the mean in a normal distribution?
+/- 68.2%
what percentage is 2SD away from the mean in a normal distribution?
+/- 95.5%
what percentage is 3SD away from the mean in a normal distribution?
+/- 99.7%
what does the frequency of IQC depend upon?
Depends on frequency of analysis
- Batch analysis requires IQC at least at the beginning and end
- Continuous flow analysis requires IQC throughout the day
what are Westgard rules?
A well established procedure that uses a set of control rules to judge the acceptability of an analytical run
what are the 2 types of errors?
- systemic
- random
what do systemic errors affect?
accuracy
what do random errors affect?
precision
what is an external quality assurance?
A retrospective review of an assay’s performance
