Lect 1 - Lab Errors

Question 1

There are many potential reasons for an erroneous laboratory test result - errors may be

Answer 1

Pre-analytical, analytical or post-analytical

Question 2

Pre-analytical errors arise from

Answer 2

Problems with sample collection and handling.

Also due to haemolysis, turbidity and icterus of sample.

Question 3

How can pre-analytical errors be minimized (8)

Answer 3

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

Question 4

Why must animals be fasted for 8hrs prior to blood sample collection

Answer 4

To avoid post prandial lipaemia

Question 5

Lipaemia can affect the values of which other components

Answer 5

Increase protein, bilirubin and calcium

Question 6

Proper blood sample collection is done via

Answer 6

Atraumatic venipuncture

Question 7

Atraumatic venipuncture minimizes what

Answer 7

Hemolysis and activation of platelets and clotting factors

Question 8

Hemolysis can cause alterations in what other components

Answer 8

Potassium (certain species), phosporus, and protein and serum enzyme activity

Question 9

In what way does haemolysis alter preanalytical results

Answer 9

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

Question 10

What kind of anticoagulant is found in a red top tube and what is it used for

Answer 10

None - serum biochemistry, urine, culture

Question 11

What kind of anticoagulant is found in a purple top tube and what is it used for

Answer 11

EDTA - CBC, cytology

Question 12

What kind of anticoagulant is found in a green top tube and what is it used for

Answer 12

Heparin - Blood gas analysis, emergency plasma chemistry

Question 13

What kind of anticoagulant is found in a light blue top tube and what is it used for

Answer 13

Sodium citrate - Coagulation studies

Question 14

What kind of anticoagulant is found in a grey top tube and what is it used for

Answer 14

Sodium fluoride/potassium oxalate - glucose determination

Question 15

To obtain 1ml of serum, what volume of blood must be collected

Answer 15

2-3ml

Question 16

How does icterus affect sample results

Answer 16

Interfere with some assays for albumin, cholesterol, glucose and total protein

Question 17

Turbidity usually a result of xs serum lipids can affect results by

Answer 17

Interfering with many spectrophotometric determination

Question 18

What is it important to include patient medication in history

Answer 18

Drugs also alter values

Question 19

Analytical errors include

Answer 19

Quality of instruments and equipment, reagents, laboratory technique and quality control program

Question 20

Post analytical errors are

Answer 20

Errors in reporting and interpreting results

Question 21

Define quality control programme

Answer 21

The detection and correction of excessive laboratory error. It is necessary to ensure that the results obtained from a laboratory are reliable

Question 22

A good quality control program should include these 3 factors

Answer 22

1. Systematic and periodic monitoring of the proper operation of equipment
2. Controls with known ranges of acceptable results for each test run in the laboratory
3. Written records

Question 23

The 2 main quality control parameters are

Answer 23

Accuracy – the extent to which measurements agree with the true value of the quantity being measured
Precision – the reproducibility of the measurements

Question 24

Reference intervals are necessary

Answer 24

For the recognition of abnormal results

Question 25

Reference intervals are based on

Answer 25

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.

Question 26

Factors that can influence/alter reference range are

Answer 26

Geographical location, season, species and breed, age, physiologic factors e.g. pregnancy and test methodologies and iatrogenic factors

Question 27

Give the absolutely ideal, realistic and minimum number of individuals which can be used for statistical analysis for reference ranges

Answer 27

120, 60, 40

Question 28

Define sensitivity

Answer 28

The frequency with which a test will be positive in patients that have disease

Question 29

Define specificity

Answer 29

The frequency with which a test will be negative in patients that do not have disease

Question 30

Define predictive value

Answer 30

The likelihood that a positive test result indicates disease or that a negative test result indicates the absence of disease