lecture 3A Flashcards

1
Q

What does analytical test mean

A

Testing a particular product

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2
Q

What does analytical test do

A

– Measure quantitatively parameters

– Higher sensitivity is better

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3
Q

What does diagnostic tests do

A

–Finding the definite answer
– Relies on cut-off which defines what is
normal and what is not
– Setting cut-off will depend on our definition
of “normal” (see lecture week 1) an idea of a normal range

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4
Q

Are Sensitivity and specificity different

for analytical or diagnostic tests

A

yes

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5
Q

What is Sensitivity in analytical definition

A

Ability of the test to detect low degrees of a particular condition.
√ Detect lower amounts/sensitivity > often are earlier diagnostic
√ often defined as 2 or more standard deviations from the signal of a zero standard

The higher the sensitivity the better

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6
Q

What are the downside of sensitivity test

A

√ Sensitive tests are often less reliable (i.e. more susceptible to external factors, needs very high and consistent skill level)
√ Sensitive tests are often more expensive
√ Sensitive tests are often more invasive

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7
Q

What role does sensitivity have if there is a large variation?

A

It will be pointless, because the result will vary a lot

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8
Q

What is the analytical definition of specificity

A

√ Is a measure of the confidence one can have
that a test measures what it is supposed to measure
√ Is a measure for the lack of cross-reaction

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9
Q

What are the drawbacks for specific test

A

More specific test have a narrower detection range in that small variations in the disease can make the disease undetectable. For
example
√ Point mutation in influenza virus
√ Different strain of HIV
√ Isolate of SARs from a different geographical region
There is no point if there are no difference in the method

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10
Q

What does cross-reaction mean

A

means disease 1 and 2 are not differentiated
If test can differentiate between disease 1 and
disease 2 there is no cross-reaction.

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11
Q

What does cross-reactivity depend on?

A

-the degree of similarity between disease 1 and disease 2. The more similar, the higher the chance of cross-reaction
-the properties of the
assay

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12
Q

Are highly (analytically) specific tests desirable?

A

• Yes, to some degree
– More specificity gives a clear picture of the disease
– Different variants may have different pathogenic outcomes
• Highly infectious vs. low infectivity
• High vs low pathogenicity
• Killing disease vs benign disease

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13
Q

What can be a problem in highly specific tests

A

Too much of a good thing
– Failure to detect minor variants will results in missed cases, need a lot of different test
– If treatment and prognosis is not different do we need to know?

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14
Q

What are some factors for analytical test

A
– Quantitative (How much?)
– Few samples
– More expensive
– Slow
– Laboratory
– External calibration/quality control
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15
Q

What are some factors for diagnostic test

A
–  Qualitative (Yes/No)
– Many samples
– Cheap
– Rapid
– Field/farm
– Within test quality control
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16
Q

What are the characteristics of a good test

A

Detect the abnormal state
• Tell us what is wrong
– How much detail do you need about what is wrong?
– Specificity
• Analytical test + Cut-off point Diagnostic test
• Can have too much sensitivity and specificity

17
Q

How to differentiate “normal” from “abnormal”

A

– Above or below threshold
– Ability to detect different pathogens
• Are similar pathogens considered as the same?
• Need to know the difference when it impacts on treatment of animal

18
Q

Waht does it mean by Minimises number if “mistakes”

A

Detect normal animal as sick

– Detect sick animal as normal

19
Q

What is a good ability to have in diagnostic

A

differentiating the healthy and the sick

20
Q

True positive for diagnostic

A

a positive result for a sample from a diseased animal

21
Q

True negative for diagnostic

A

a negative result for a sample from a normal animal

22
Q

False positive for diagnostic

A

a positive result for a sample from a normal animal

23
Q

False negative for diagnostic

A

a negative result for a sample from a diseased animal

24
Q

What is the formula of diagnositic sensitivity

A

– True positive/total number of diseased animals
– True positive/(true positive + false negatives)
Diagnostic sensitivity = TP/(TP + FN) in respect to sick animals

-Diagnostic sensitivity = TN/(TN + FP)

25
Q

What is the diagnostic sensitivity for

A

Probability that diagnostic test is positive in the presence of disease
- to find out how accurate the tests are

26
Q

How to set a cut-off point When healthy and diseased overlap

A

– Concessions have to be made
– Where the cut-off is set depends on the use of
the test:
• Diagnosis of individual animal
• Screening for disease presence
• Monitoring whether disease entered the country

27
Q

When do you want to maximise true positive

A

When disease is treatable or medicine is safe, cost of false positive is high

28
Q

When do you want to maximise true negative

A

disease is not treatable, cost of false positive is high

29
Q

When should you have a medium specificity cut-off

A

when effect of false positive and false negatives is equally bad