Diagnosis of exclusion

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.^[1]

Diagnosis by exclusion tends to occur where scientific knowledge is scarce, specifically where the means to verify a diagnosis by an objective method is absent. 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]