Differentials in the “trash” zone are considered
ruled out or excluded
if the probability of disease is below the testing thresholds:
- stop doing tests related to that specific differential diagnosis
Factors to consider when establishing a threshold:
- the condition: harms of ruling out a diagnosis that may be present
- The test: how harmful is the test and how much information will it provide?
Harms include: financial, time and other
Consider the patient values and preferences
Should not set the testing threshold below the population ___________.
population prevalence
This would suggest that you think someone take at random from the population is in the testing zone, implying at least that you think everyone who walks into your office should be investigated for the condition
ASK yourself: “Would I be comfortable sending the patient
home with an x% chance that they had this condition when
[some test] is available?”
The test zone expands (and “trash” zone shrinks) if:
- greater harm of ruling out the condition if it is present
- more favourable balance of test harm relative to information benefit
The “trash” zone expands (and test zone shrinks) if:
- less harm of ruling out the condition if it is present
- less favourable balance of test harm relative to information benefit
________ thresholds set a probability below which we stop
diagnostic work-up. We do this because complete certainty is
impossible
testing thresholds
Testing thresholds are set according to the harm of
inappropriately ruling _____ a diagnosis and the ______ of the
harms and benefits of testing
ruling out
the balance of the harms and benefits of testing
When the probability of disease is above a testing threshold,
___________ is needed. When it is
below a testing threshold, we _____ the diagnostic work-up for that
condition.
further testing or other management is needed. when below, we stop
