Study highlights utility of CDS for diagnosing major depression

In the last 2010 issue of Psychotherapy and Psychosomatics, a new scale for measuring depression in cardiac patients is presented.

The Cardiac Depression Scale (CDS) was initially developed specifically for cardiac patients. Its purpose is to allow measurement over the continuum between low-level depressive symptomatology and major depression. The Authors of this study aimed to evaluate the criterion-related validity of the CDS and thus determine optimal CDS cutoff scores for detecting major depression for both two-stage screening in clinical settings and single-stage screening in epidemiological research settings.

Two hundred and fifteen patients were recruited from the cardiology service of a major secondary and tertiary referral hospital. The CDS comprises 26 items, each answered on a 7-point Likert-type scale, with responses ranging from 'strongly disagree' (1) to 'strongly agree' (7). To avoid a response set, 7 of the 26 items are worded in a positive direction and the overall score is calculated by summing across all items after reversing positively worded items, with scores ranging from 26 to 182.

A higher total score reflects more severe depressive symptoms. The Mini International Neuropsychiatric Interview (MINI) was used as the external criterion measure to determine the categorical presence of major depression. The concurrent component of criterion validity was examined by assessing how well the CDS was able to detect the category of major depression using the structured interview as the external criterion.

Receiver operating characteristic curves were constructed for determining the optimal sensitivity and specificity and the area under the curve. For clinical two-stage screening, it is suggested that a cutoff score should provide maximum sensitivity with at least 75% specificity so as to limit false negatives while also preventing an inordinate number of false positives.

It is also important to propose cutoff scores which are rounded and recognizable numbers in order to aid administration and interpretation of a scale. The Authors chose to recommend CDS cutoff scores that are a multiple of 5 rather than cumbersome scores based solely on the statistics.

CDS cutoff scores for clinical settings (two-stage screening) were derived by considering the cutoff score which provided maximum sensitivity with ≥ 75% specificity and then rounding to the nearest multiple of 5. For estimating the prevalence of depression in research settings, where overall diagnostic accuracy rather than just sensitivity is important, the Authors derived a CDS cutoff of ≥ 95 for major depression, which gives 97% sensitivity and 85% specificity.

This study demonstrates the utility of the CDS for diagnosing major depression. The investigators have produced CDS cutoff scores for major depression that can be used effectively in routine clinical diagnosis as well as in future epidemiological and clinical studies. As the CDS was designed for cardiac patients, further validation in other medical populations with a high incidence of comorbid depression is warranted.