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The key to screening
decisions is estimating potential benefit relative to harms and
costs.
| Key
Principles of Screening
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- Benefits
accrue only to individuals who have the sought-for
disease.
- Harms
and costs can affect every person screened.
- Therefore,
the benefits of screening a population increase
relative to harms as the prevalence of the disease
increases.
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Since the risk of many
diseases increases with age, it would initially appear that the
elderly should benefit more than younger people from screening.
However, other consequences of advancing age reduce the benefit
of screening in the elderly. The most important is chronic disease.
Anyone can die of other
diseases before experiencing the benefit of screening, but this
problem is much worse for the elderly because so many have chronic,
ultimately fatal, disease. This leads to a key principle of screening
in the elderly:
| Key
Principles of Screening
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Many
older people undergo screening for a disease that
they might have, and then die of a disease that they
do have before screening could possibly help them.
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Clinical trials of
screening often show that the screened group and the control group
die at the same rate for at least 5 years. For example, the table
below shows the delay in benefit for three common screening procedures.
The harms of screening, follow-up testing, and subsequent treatment
increase for the elderly for several reasons:
- The hardship of
undergoing a screening test, follow-up testing ,and treatment
is greater for the elderly due to:
- Physical
and cognitive limitations
- Problems
getting transportation
- Difficulty
adhering to the preparations required for some tests
- These harms and
burdens are more immediate, and more certain, than the benefits.
Therefore, many patients
will view the balance between benefit and harm as shifting
towards net harm.
For older individuals, the decision about who will benefit from
a screening test depends on the ability to estimate life expectancy.
Therefore, the methods used to determine life expectancy are of
crucial importance, and are addressed in sections that follow.
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