Original Article
Summed score of the Patient Health Questionnaire-9 was a reliable and valid method for depression screening in chronically ill elderly patients

https://doi.org/10.1016/j.jclinepi.2007.07.018Get rights and content

Abstract

Objective

To assess the psychometric properties of the Patient Health Questionnaire-9 (PHQ-9) as a screening instrument for depression in elderly patients with diabetes mellitus (DM) and chronic obstructive pulmonary disease (COPD) without known depression.

Study Design and Setting

DM and COPD patients aged >59 years were selected from general practices. A test–retest was conducted in 105 patients. Criterion validity, using the Mini International Neuropsychiatric Interview psychiatric interview to diagnose major depressive disorder (MDD) and any depressive disorder (ADD) as diagnostic standard, was evaluated for both summed and algorithm-based PHQ-9 score in 713 patients. Correlations with quality of life and severity of illness were calculated to assess construct validity.

Results

Cohen's kappa for the algorithm-based score was 0.71 for MDD and 0.69 for ADD. Correlation for test–retest assessment of the summed score was 0.91. The algorithm-based score had low sensitivity and high specificity, but both sensitivity and specificity were high for the optimal cut-off point of 6 on the summed score for ADD (Se 95.6%, Sp 81.0%). Correlations between summed score and quality of life and severity of illness were acceptable.

Conclusion

The summed PHQ-9 score seems a valid and reliable screening instrument for depression in elderly primary care patients with DM and COPD.

Introduction

Major depressive disorder (MDD) is a common disorder in aging populations, with reported prevalence rates of 1–2% [1], [2], [3]. Minor depression, defined as depressive symptoms that do not meet the criteria for major depression, is present in 10–15% of elderly persons [1], [2], [3]. In elderly persons with chronic illnesses, the prevalence of depression is even higher [4], [5], [6], [7]. Both major and minor depression are associated with a decreased quality of life, increased morbidity risk, increased functional disability, increased health care utilization, and increased medical costs [8], [9], [10], [11], [12], [13], [14]. Depression also impairs one's ability to adhere to disease management regimens (diet, exercise, quitting smoking, taking medication regularly), potentially worsening the course of the chronic illness [15], [16]. When depression coexists with chronic illnesses, this may even cause a downward spiral, because depression and disability mutually reinforce each other [14], [17], [18]. Therefore, recognition and treatment of depression in chronically ill elderly patients is important.

Treatment of depression comprises of antidepressants and psychological treatments. In minor depression, psychological treatments are preferred according to clinical guidelines [19], [20], and also a recent meta-analysis stressed that prevention of depressive disorder seems possible [21].

However, depression in elderly patients often remains unrecognized and untreated in primary care [22]. Having a somatic illness may further increase the risk of a prevalent depression remaining undetected, because depression and depressive symptoms hardly receive any attention in current clinical guidelines for chronic somatic illnesses [23], [24], [25]. General practitioners often have limited time and patients may not always explicitly present their depressive symptoms, or may even mask these symptoms.

The use of short screening questionnaires, like the Patient Health Questionnaire-9 (PHQ-9), may be helpful in improving the recognition of depression. The PHQ-9 is a short self-administered questionnaire consisting of nine items asking for the presence of depressive symptoms. The items run parallel to the nine symptoms of depression as described in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) and in the guidelines of the College of Dutch GPs (NHG) [20], [26]. It has been validated for both diagnosing depression and determining the severity of depression in primary care settings [27], [28], [29]. Recently, studies showed the PHQ-9 to be valid and reliable as a screening instrument in populations with stroke [30], traumatic brain injuries [31], and spinal cord injuries [32]. Only one study evaluated the PHQ-9 in a depressed elderly population with on average 3.2 comorbid medical conditions [33]. However, this study did not evaluate the PHQ-9 for screening purposes, but for assessing treatment outcome in a sample of elderly patients already diagnosed with a depression. To our knowledge, the PHQ-9 has not been validated as screening instrument in an older population with somatic chronic illnesses, such as diabetes mellitus (DM) and chronic obstructive pulmonary disease (COPD). Because symptoms of DM and COPD may overlap with symptoms of depression and because a stigma still exists on mental health problems in older patients, recognition and screening may be more difficult in these groups.

The purpose of the present study is to evaluate the criterion validity, construct validity, and reliability of the PHQ-9 as a screening instrument in a population of elderly patients with DM type II and COPD without known depression.

Section snippets

General design

As part of the Delta study [34], an randomized controlled trial (RCT) to evaluate the effectiveness of a nurse-led minimal psychological intervention for chronically ill older patients with comorbid depression, we conducted this study to test whether the PHQ-9 is a valid and reliable screening instrument for depression in chronically ill elderly people. To do so, we tested the reliability, construct validity, and criterion validity.

A test–retest assessment of the PHQ-9 was conducted to evaluate

Patient characteristics

Mean age of the sample (n = 713) was 71.4 years (SD 6.9), 51.2% of the patients had DM, 51.8% were male, and 40.1% had primary education only. PHQ-9 depressed patients more often had only received primary education than nondepressed patients (41.7% vs. 27.0%, P = 0.001). In the total sample, 19.3% had ADD and 10.7% had MDD according to the PHQ-9. Of the DM patients, 17.3% had ADD according to the PHQ-9, whereas in COPD patients 22.2% had ADD (P < 0.001). MDD according to the PHQ-9 was present in 9.1%

Discussion

The purpose of this study was to evaluate the validity and reliability of the PHQ-9 in a population of elderly patients with DM and COPD without known depression. Except for a lower reliability for MDD in DM patients, test–retest reliability was found to be high. When using the scoring algorithm, the specificity was high, meaning that the PHQ-9 produces only a relatively small number of false positives. However, sensitivity was low, meaning that a large number of patients with an actual

Acknowledgment

The Delta study was funded by the Netherlands Organisation for Health Research and development (ZonMW), grant number 945-03-047.

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