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In the absence of data
from clinical trials, physicians and patients must make screening
decisions on a patient-by-patient basis. The most useful heuristic
in this setting is to compare the harms and costs of screening
with the benefits for each patient using the following steps.
Estimate the individual's
risk for the condition in question.
- Low or normal risk: screening may no longer be warranted,
especially in light of normal past screening tests.
- High risk: estimate the patient's likelihood of benefiting
from further screening (see below).
Estimate the patient's life expectancy.
- Determine the patient's physiological age, using chronological
age and self-reported current state of health.
- Estimate the patient's life expectancy from their physiological
age using the life expectancy estimates for different ages.
For the disease you are screening for, determine the delay
between initiating screening and observing a reduction in disease-specific
mortality.
- If you are unsure, base your estimate on experience with
other diseases, which is typically about five years.
- If the patient's life expectancy is longer than the expected
delay until benefit, the patient is a candidate for screening.
Assess the patient's attitudes toward the inconveniences and
harms of screening and subsequent testing and treatment.
The theory behind this
method for calculating life expectancy in a person with a serious
illness is interesting and is explored in greater detail in the
next section, "Co-morbid Illness and Decision Making. "
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