Background:

Since the 1950's researchers have been trying to standardize the way schizophrenia is diagnosed. We recently completed six Cochrane Reviews assessing the accuracy of four checklists (First Rank Symptoms, OPCRIT+, K-SADS and CIDI), magnetic resonance imaging (MRI) and blood tests to diagnose schizophrenia.

Objectives:

To report the challenges we encountered while performing diagnostic test accuracy (DTA) reviews in schizophrenia.

Challenges:
1. Despite using wide search parameters, we were unable to find many studies whose primary aim was to test diagnostic accuracy. This is perhaps not surprising for older checklists, but also newer, widely used checklists lack DTA studies, as do the very newest proposed diagnostic techniques.

2. As in most mental health disorders, there is no objective reference standard for diagnosing schizophrenia. Instead, diagnosis is made by a psychiatrist based on clinical interviews and patients’ medical history, but disagreements are common among psychiatrists. We provided some insight into whether research should focus on a single test (clinical examination) or a combination of tests (e.g. clinical examination + checklists + MRI).

3. Our main challenge was how to apply DTA methods, particularly quality assessment. Most of the included studies did not state whether all participants had psychotic symptoms; often a diagnosis of schizophrenia was retrospectively compared to the participant’s clinical examination. Some studies included all admissions to psychiatric close wards, and we assumed that the majority of patients would have psychotic symptoms. Often details of the reference standard were unclear, with studies simply stating that participants were diagnosed according to DSM or ICD diagnostic criteria.

Conclusions:

There is a lack of research assessing the diagnostic accuracy of tests in schizophrenia, which is probably due to a lack of understanding to what causes schizophrenia. In the real world diagnoses have to be made and the lack of appropriate studies might result in new tests being ‘crept’ into practice in the absence of evaluation and without regard to the consequences of erroneous diagnoses.