Screening Flashcards

1
Q

What is screening

A

Screening is the practice of investigating apparently healthy individuals with the object of detecting unrecognised disease
or its precursors in order that measures can be taken to prevent or delay the development of disease or improve

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2
Q

Screening test and diagnostic test difference

A

Diagnostic tests normally give you more definite answers of whether or not you have the disease. Results from screening normally only give you a ‘risk’ e.g. high levels of x means your more likely to get a disease

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3
Q

What does validity mean for a test?

A

ability to distinguish between who has a disease and who does not and has 2 components: sensitivity and specificity

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4
Q

What is sensitivity of a screening test

A

Ability to pick up true positives

Of those who have the disease, how many of them are picked up by the test

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5
Q

What is specificity of a screening test

A

ability to exclude true negatives

Of those who do not have the disease, how many of them were actually excluded by the screening test

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6
Q

What is positive predictive value

A

Of those who tested positive, how many of them were true positives

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7
Q

What is negative predictive value

A

Of those test negative, how many of them are true negatives

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8
Q

examples of diseases screened during antenatal screening?

A

Split into 4 groups:
Chromosomal, Downs Pataus and Edwards
Infections: syphilis, HIV, Hep B
Physical abnormalities (anomaly scan)
Metabolic: phenylketonuria (PKU) and hypothyroidism
Haemoglobinopathies: Sickle cell disease andthalassaemia

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9
Q

Examples of newborn screening

A

Physical exam (includes eyes, heart, hips, testes)
• Hearing test
• Blood spot (for rare metabolic conditions) - also called heel prick test

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10
Q

Examples of adult cancer screening in UK

A

Breast (women 50 – 70)
• Cervical (women 25 – 64)
• Bowel (men and women 60 – 74)

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11
Q

What is lead time bias?

A

Early diagnosis results in increase in time from diagnosis to death even if natural history of disease is unaltered by intervention. This may be result in an apparent improvement in length of survival when it is due to the fact that it was diagnosed early

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12
Q

What is selection bias in terms of screening

A

Those who attend screening are likely to be different to those who dont attend screening

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13
Q

What is length bias

A

Length bias exists as some conditions may be slower in developing to a health threatening stage, that is, they have a longer preclinical stage. This means they are more likely to be detected at that stage but they may also have a more favourable prognosis compared to fast developing diseases.This may lead to the false conclusion that screening is beneficial due to the fact that there is a disproportionately larger proportion of slow developing cases captured by the screening compared to fast growing cases

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14
Q

Three types of biases that can arise in screening

A

length bias
lead time bias
selection bias

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15
Q

What are predictive values dependent on?

A

dependent on sensitivity, specificity, and the prevalence of disease ( see example in iBOOK)

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16
Q

What curves are used to determine cut off values in a diagnostic test? What are the labels on the axis ?

A

ROC curves
used in medicine to determine a cut-off value for a diagnostic or screening test. The ROC curve is a graph of sensitivity (y-axis) vs. 1-specificity (x-axis). The choice of a particular cut-off value for a test is informed by the attempt to maximize sensitivity and specificity.

17
Q

Screening can be targeted to the whole population or just to a specific group of people. What do you call these ?

A

Mass screening- whole population

targeted screening- specific group

18
Q

Within each of these types of screening, how can they be further subdivided?

A

Mass and targeted screening can each be subdivided into systematic and opportunistic
Systematic= when people are called for screening in a systematic way
opportunistic = eg chlamydia screening in the young people where patients present to doctors and then doctor offer them screening

19
Q

What is the criteria for screening to be offered for a disease? Consider factors relating to the disease itself, the diagnostic test and the potential treatment options

A

Disease:

  • important health problem
  • well recognised and detectable pre-clinical stage
  • natural history of disease understood
  • long period between first signs and proper presentation of disease
Diagnostic test:
valid- sensitive and specific
simple + cheap
safe 
reliable
Diagnosis and treatment:
adequate facilities 
effective, acceptable and safe treatment available
cost effective
sustainable
20
Q

What are the ethical problems surrounding screening?

A

Screening itself and the diagnostic tests following it may have risks attached

False positive may give unnecessary anxiety
false negative may give unnecessary reassurance

21
Q

What does ‘gold standard’ mean?

A

a recognised way of determining who really has the disease