Lect 1 - Lab Errors Flashcards
There are many potential reasons for an erroneous laboratory test result - errors may be
Pre-analytical, analytical or post-analytical
Pre-analytical errors arise from
Problems with sample collection and handling.
Also due to haemolysis, turbidity and icterus of sample.
How can pre-analytical errors be minimized (8)
Animal fasted 8hrs prior collection of blood Avoid xs stress Proper sample collection technique Proper collection container and use of coagulants Proper labeling of all specimens Proper storage of the sample Adequate volume of samples for assay Prompt proessing
Why must animals be fasted for 8hrs prior to blood sample collection
To avoid post prandial lipaemia
Lipaemia can affect the values of which other components
Increase protein, bilirubin and calcium
Proper blood sample collection is done via
Atraumatic venipuncture
Atraumatic venipuncture minimizes what
Hemolysis and activation of platelets and clotting factors
Hemolysis can cause alterations in what other components
Potassium (certain species), phosporus, and protein and serum enzyme activity
In what way does haemolysis alter preanalytical results
Releasing intracellular constituents into the serum thereby increasing their values
Diluting serum constituents thereby lowering their values
Directly interfering with colorimetric quantitation based on protein binding or formation of coloured complexes
What kind of anticoagulant is found in a red top tube and what is it used for
None - serum biochemistry, urine, culture
What kind of anticoagulant is found in a purple top tube and what is it used for
EDTA - CBC, cytology
What kind of anticoagulant is found in a green top tube and what is it used for
Heparin - Blood gas analysis, emergency plasma chemistry
What kind of anticoagulant is found in a light blue top tube and what is it used for
Sodium citrate - Coagulation studies
What kind of anticoagulant is found in a grey top tube and what is it used for
Sodium fluoride/potassium oxalate - glucose determination
To obtain 1ml of serum, what volume of blood must be collected
2-3ml
How does icterus affect sample results
Interfere with some assays for albumin, cholesterol, glucose and total protein
Turbidity usually a result of xs serum lipids can affect results by
Interfering with many spectrophotometric determination
What is it important to include patient medication in history
Drugs also alter values
Analytical errors include
Quality of instruments and equipment, reagents, laboratory technique and quality control program
Post analytical errors are
Errors in reporting and interpreting results
Define quality control programme
The detection and correction of excessive laboratory error. It is necessary to ensure that the results obtained from a laboratory are reliable
A good quality control program should include these 3 factors
- Systematic and periodic monitoring of the proper operation of equipment
- Controls with known ranges of acceptable results for each test run in the laboratory
- Written records
The 2 main quality control parameters are
Accuracy – the extent to which measurements agree with the true value of the quantity being measured
Precision – the reproducibility of the measurements
Reference intervals are necessary
For the recognition of abnormal results
Reference intervals are based on
Samples from a group of healthy animals – animals included should be representative of the animals that the reference range is expected to be used for.
Reference intervals represent the results we expect to find to in healthy animals, and represent 95% of the healthy population.
Factors that can influence/alter reference range are
Geographical location, season, species and breed, age, physiologic factors e.g. pregnancy and test methodologies and iatrogenic factors
Give the absolutely ideal, realistic and minimum number of individuals which can be used for statistical analysis for reference ranges
120, 60, 40
Define sensitivity
The frequency with which a test will be positive in patients that have disease
Define specificity
The frequency with which a test will be negative in patients that do not have disease
Define predictive value
The likelihood that a positive test result indicates disease or that a negative test result indicates the absence of disease
