DIFFERENTIAL DIAGNOSIS

From Users’ Guides to the Medical Literature Evidence-Based Medicine Working Group

Are the Results Valid?

Did the study patients represent the full spectrum of those who present with this clinical

problem?

Were the criteria for each final diagnosis explicit and credible?

Was the diagnostic work-up comprehensive and consistently applied?

For initially undiagnosed patients, was follow-up sufficiently long and complete?

What are the Results?

What were the diagnoses and their probabilities?

How precise are these estimates of disease probability?

Will the Results help Me in My Patient Care?

Are the study patients similar to my own?

Is it unlikely that the disease possibilities or probabilities have changed since this

evidence gathered?

Reference: JAMA 1999 281:1214-1219

Differential Diagnosis for a Specific Patient

Diagnostic Hypothesis	Description	Implications for Testing
1. Leading hypothesis, or “working diagnosis”	Single best explanation of patient’s illness	Choose tests to confirm: High specificity High LR+ (>>1)
2. Active alternatives, or “rule outs”	Not as good as No. 1, but likely, serious or treatable enough to be actively sought in this patient	Choose tests to exclude: High sensitivity Low LR-(<<1)
3. Other alternatives	Not likely, serious or treatable enough to be pursued now, but not yet excluded	Hold off on tests now (may test for these later)
4. Excluded hypotheses	Causes of the problem that have been disapproved	No further tests necessary