Introduction to Clinical Chemistry

Question 1

Define accuracy

Answer 1

How close is the test to the true value

Question 2

Define precision

Answer 2

How close are repeated measurements to one another

Question 3

What is linearity

Answer 3

Is the response proportional to the analyte

Question 4

Define interference

Answer 4

Is the test affected by other factors such as haemolysis, icterus or lipaemia

haemolysis = red tint
Icterus = excessive bilirubin
Lipaemia = excessive lipids

Question 5

What is analytical sensitivity?

Answer 5

What is the smallest amount that you can measure

Question 6

What is analytical specificity

Answer 6

Does the method measure the correct analyte e.g. if on steroids cortisol will be high and won’t indicate cushings disease

Question 7

What is the equation for finding the mean (accuracy)?

Answer 7

(sum of xi)/n

Question 8

What is the equation for finding precision/SD?

Answer 8

Square root of (sum of (x-xbar)^2/n-1)

Question 9

How do you find the coefficient of variation

Answer 9

Standard deviation/mean x 100

Question 10

What is a reference range

Answer 10

A set of values obtained from a group of individuals of defined health status

Question 11

List the factors that influence reference ranges

Answer 11

Age
Gender
Weight
Diet
Pregnancy
Menstrual Status
Time of day
Time of year

Question 12

What can be used instead of reference ranges

Answer 12

Action limits
Therapeutic ranges

Question 13

What are action limits

Answer 13

means the minimum and maximum values of a quality assurance measurement

If the analyte is higher than the action limit then you need to intervene e.g. paracetamol overdose

Question 14

What is a therapeutic window

Answer 14

Has a min and max
Need to get patients within this range
If too high there is toxic side effects
If too low the drug is not effective

Question 15

Where are the four sources of variation in laboratory medicine

Answer 15

Biological variation
Pre-analytical variation
Analytical variation
Post-analytic variation

Question 16

Give some areas where there is pre-analytical variation
(7)

Answer 16

Type of sample -> venous or capillary

Collection tube

Fasting or not

Specimen handling -> labelling, transport and storage

Strenuous exercise

Unreadable information on sample

Old sample

Question 17

What are the two ways of biological variation

Answer 17

Interindividual
Intraindividual

Question 18

What is interindividual variation

Answer 18

A patient values compared to a population mean

Question 19

What is intraindividual variation
(3)

Answer 19

A patient compared to themselves

Usually smaller variation than interindividual

e.g. bilirubin drops during the day

Question 20

What is a panel approach

Answer 20

Combining multiple tests to address a clinical question

e.g. lipid profile or liver profile

Question 21

What is an ideal diagnostic test

Answer 21

No overlap between values from healthy and diseased populations but this very rarely happens

Question 22

What happens when there is overlap in a test

Answer 22

Generates some false positives and negatives

Question 23

What is a cutoff point

Answer 23

Arbitrary value that marks the point between negative and false e.g. in pregnancy levels double every 24 hours

Question 24

What is diagnostic sensitivity

Answer 24

Frequency of positive test result when disease present

Question 25

What is diagnostic specificity

Answer 25

Frequency of negative test result when disease absent

Question 26

What is diagnostic specificity

Answer 26

Frequency of negative test result when disease absent

Question 27

What is the equation for diagnostic sensitivity?

Answer 27

True positives/(true positives + false negatives)

Question 28

What is the equation for specificity?

Answer 28

True negatives/(true negatives + false positives)

Question 29

What is positive predictive value

Answer 29

Tells you the odds of you having the disease if you have a positive result

Question 30

What is negative predictive value

Answer 30

Tells you the odds of you not having a disease if you have a negative result

Question 31

What is the equation for positive predictive value?

Answer 31

Positive test result with disease + positive test without disease

Question 32

What is the equation for negative predictive value?

Answer 32

negative test with disease + negative test with disease

Question 33

What is sensitivity in terms of a question to ask yourself

Answer 33

I know my patient has the disease. What is the chance that the test will show that my patient has it?

Question 34

What is specificity in terms of a question to ask yourself

Answer 34

I know my patient doesn’t have the disease. What is the chance that the test will show that my patient doesn’t have it

Question 35

What is PPV in terms of a question

Answer 35

I just got a positive test result back on my patient. What is the chance that my patient actually has the disease

Question 36

What is NPV in terms of a question you can ask yourself

Answer 36

I just got a negative test result back on my patient. What is the chance that my patient actually doesn’t have the disease

Question 37

How do you define and determine reference intervals
(7)

Answer 37

Reference individuals

Make up a reference population

From whom are selected a reference sample group

On whom are determined reference values

On which is observed a reference distribution

From which are determined reference limits

That define a reference interval