A diagnosis of exclusion or by exclusion (per exclusionem) is a diagnosis of a medical condition reached by a process of elimination, which may be necessary if presence cannot be established with complete confidence from history, examination or testing.
Such elimination of other reasonable possibilities is a major component in performing a differential diagnosis.
It can also commonly occur where objective diagnostic tests do exist, but extensive diagnostic testing or sufficient exploration of differential diagnosis by a multidisciplinary team is not undertaken due to financial constraints or assessment bias (health inequity).
[2][3][4][5][6] The largest category of diagnosis by exclusion is seen among psychiatric disorders where the presence of physical or organic disease must be excluded as a prerequisite for making a functional diagnosis.
[7][8] An example of such a diagnosis is "fever of unknown origin": to explain the cause of elevated temperature the most common causes of unexplained fever (infection, neoplasm, or collagen vascular disease) must be ruled out.