1. Quality Assurance in the clinical laboratory
Lecture 1

2. Types of Errors
Mistakes jeopardize patient care and must be detected and avoided at all times
They are two types of errors:
random errors
systematic errors

3. Random Errors Occur without prediction or regularity
Affect precision of measurement and causes data to be scattered more
Random errors occur as the result of:
Carelessness,
when taking short cuts in procedures,
Mislabeling specimens,
Incorrect filing of reports,
Reporting of wrong result to the wrong patient

4. Systematic Errors Errors within the test system or methodology
Affect the accuracy of results
Causes the mean of a data set to differ from the accepted value
Examples include:
Incorrect instrument calibration
Unprecise or malfunctioning dilutors and pipettes
Reagents that lost their activity

5. Systematic Errors Types of systematic errors
proportional systematic error or bias
It grows larger as the concentration of analyte grows
constant systematic error "constant bias"
A constant amount over the entire range of the analysis process.

6. Choice of Methods and Instruments
Quality Assurance
Choice of Methods and Instruments

7. Experiments and type of error which can be detected

8. Method Evaluation- Comparison of Methods
One of the easiest methods is to plot the results on a scattergram
Draw the best straight line through the points and determine the slope and intercept of the line
The slope and intercept offer a fair evaluation of the agreement between the methods

9. Comparison Of Methods
Perfect correlation (Hypothetical) Slope (b) = 1 Y intercept (a) = 0 Correlation coefficent (r) = 1

10. Quality Assurance of Reagents, Supplies, And Laboratory Water

11. Laboratory Water
Reagent - grade water must be properly purified and periodically inspected for:
Electrical resistivity
Resistivity (R) of water is the measurement of electrical resistance and is the inverse of electrical conductivity (C)
R and C are directly related to the number of inorganic ions and conduction particles in the water
The greater the ionic concentration, the greater the electrical conductivity and the less the electrical resistance
Measurements are made using a resistivity or conductivity meter
Soluble silica concentration
measured by a chemical reaction between silicate and molybdate ions to form a blue complex

12. Laboratory Water
Desired pH
The pH is measured with pH meter
Bacterial contamination
The microbiological content of the water is defined as the number of colony - forming units per milliliter of water
Three recommended methods:
Pour plate (1 ml of water)
membrane filtration
or calibrated loop for sampling (0.01 ml)
If organic free water is desired , soluble organic materials can be removed using charcoal filter

13. QUALITY ASSURANCE IN THE CLINICAL CHEMISTRY LABORATORY

14. Sources of Error in Clinical Chemistry
1. Specimen mix-up
A Specimen drawn from wrong patient
Specimen labeled with the wrong name or accession numbers
Serum transferred into mislabeled tubes
Improper cup placed into a tray position and the results reported on the wrong patient
2. Allowing evaporation of a sample while it sits on the analyzer waiting to be analyzed
This will concentrate the sample, resulting in higher values
3. Dilution and calculation errors
Incorrect dilution of sample
Failure to correct for dilution

15. Sources of Error in Clinical Chemistry
4. Sampling errors
Partially clotted specimen
Short sampling
Air bubble in the bottom of the cup
Fibrin clot in the sample probes
5. Transcription errors
6. Instrument losing calibration due to:
dirty reaction cuvettes,
or worn pump tubing;
7. Instrument is not recalibrated when new reagents are placed on the instrument
This can result in a shift in the calibration