Depression can be difficult to detect and diagnose and this difficulty only increases when other mental health conditions are also present.

This systematic review conducted by a team of researchers from Groningen in the Netherlands, set out to identify the best instrument for diagnosing depression in people with schizophrenia. Their concern was that some diagnostic tools developed for use in depression patients may not discriminate between depressive symptoms and the negative psychotic symptoms that are often present in schizophrenia.

The researchers conducted a broad search and found 48 papers that measured the reliability and validity of 6 depression instruments for patients with schizophrenia:

1. Beck Depression Inventory (BDI)
2. Brief Psychiatric Rating Scale-Depression subscale (BPRS-D)
3. Positive and Negative Syndrome Scale-Depression subscale (PANSS-D)
4. Hamilton Rating Scale for Depression (HAMD)
5. Montgomery Asberg Depression Rating Scale (MADRS)
6. Calgary Depression Scale for Schizophrenia (CDSS)

The Beck Depression Inventory was the only one of the 6 instruments that used a self-reporting mechanism to measure the extent of the depressive illness. The other 5 were all clinician rated scales.

Here’s what they found with their review:

• All 6 instruments reliably measured depressive symptoms in patients with schizophrenia
• The Calgary Depression Scale for Schizophrenia most accurately:
• differentiated depressive symptoms from other symptoms of schizophrenia (divergent validity)
• correlated well with other depression instruments (concurrent validity)
• and was least likely to miss cases of depression or misdiagnose depression (predictive validity)

The authors concluded:

We would recommend to use the Calgary Depression Scale for Schizophrenia for the measurement of depressive symptoms in research and in daily clinical practice of patients with schizophrenia. A valid self-report instrument is to be developed for the use in clinical practice.

Lako IM, Bruggeman R, Knegtering H, Wiersma D, Schoevers RA, Slooff CJ, Taxis K. A systematic review of instruments to measure depressive symptoms in patients with schizophrenia. J Affect Disord. 2011 Nov 17. [PubMed abstract]