Labs 1 & 2 Flashcards
Calibration
the act of ensuring that a scientific process or instrument will produce accurate results every time
This is done by testing standards (calibrators) of known concentrations to verify the ability of the instrument to produce results
Establishes linearity
Performed as needed
Pure substance testing specific to 1 analyte
Standard
A highly purified chemical that has an exact known concentration and purity
Different number of calibrators ran based on:
Test type
Range of results
Manufacturers
Single Point Calibration
Not routinely done on advanced chemistry analyzers
Mainly seen on point of care (POC) analyzers and scales
Two Point Calibration
Mainly performed on qualitative assays like drugs of abuse
Multi-Point Calibration
Used on most assays performed on advanced analyzers
Strengthens linearity for assays with a wider range and in analytes were knowing the exact result is imperative
QC
The process of monitoring and assessing the analytical phase of testing using materials to assess all testing parameters (i.e. reagents, calibrations, temperature, etc.)
Common practice is to run multiple levels of QC for an assay
Verifies all testing parameters
Performed with at least each run of patients or daily
Not analyte specifc
Number of levels and frequency of QC runs depends on
How often the assay is ran on patients
Quantitative v.s Qualitative Assays
Manufacturer specifications
Levey-Jennings Charts
Graphical representation of observed values of a quality control material over time in the context of the upper and lower control limits
Accuracy
How close a measured value is to it’s true value
Precision
Dispersion of repeated measurements about the mean
Random Error
Error resulting from a variation in technique, a one off
Running wrong QC material
Systemic Error
Constant error that occur due to issues with instrumentation such as procedures, standards, reagents, etc.
Bad calibration
Shift
an abrupt change in the analytic process
Trend
A gradual change in the analytic process
Glucose
Glucose Oxidase Reaction
Measure Serum or plasma
Sodium fluoride (inhibits glycolytic enzymes) for samples with delayed analysis
Falsely decreased by increased bilirubin, uric acid, and ascorbic acid. Also samples not centrifuged immediately (within 1 Hour)
Strong oxidizing agents like bleach cause falsely high results. Also hemolyzed samples
Fasting samples should be an overnight 8-10 hr fast, no more than 16 hrs
2 Hour Glucose Testing
- Fasting glucose is taken
- Patient consumes 75 g glucose drink
- Glucose is retested 2 hr later, every hour for pregnant women
Glycosylated Hemoglobin/ HbA1c uses EDTA whole blood
BE SURE TO REVIEW ACTUAL LAB SHEETS
What does a Lipid panel consist of?
Total Cholesterol
HDL- Cholesterol
LDL- Cholesterol
Triglycerides
Cholesterol
Measure Serum or plasma from a 12 hour fast
Gas chromatography- mass spectrometry is the reference method
Reducing agents like vitamin C and bilirubin can cause interference
HDL & LDL measured based off their cholesterol content
Triglyceride
Used to help estimate LDL
Significantly increases after a meal
Glycerol can cause interference
Gas chromatography- mass spectrometry is the reference method
HDL
Modern methods use homogenous assays (does not require a physical separation of the free and bound labeled analyte)
Known to lack specificity in unusual patients like patients with kidney/liver diseases
LDL
Method combines ultracentrifugation with precipitation
Most labs rather use Friedewald calculation to estimate LDL
LDL = total cholesterol - HDL - Trig/5
BE SURE TO REVIEW HOMEWORK AND REVIEW QUESTIONS
Why do we do QC if calibration verifies the testing abilities of the instrument?
QC verifies calibration or linearity
