Research Report
Subthreshold anxiety better defined by symptom self-report than by diagnostic interview

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Abstract

Background

There is no consensus on how to define subthreshold anxiety. Based on functional impairment, we aim to evaluate the use of a diagnostic instrument and an anxiety severity questionnaire to derive an empirical cut-off for defining clinically relevant, subthreshold anxiety.

Methods

Our sample consisted of 1788 subjects without full-syndromal anxiety disorders from the Netherlands Study of Depression and Anxiety (NESDA). We used ANCOVA to compare the Composite International Diagnostic Interview (CIDI) and the Beck Anxiety Inventory (BAI) in their association with functional impairment, measured by the World Health Organization Disability Assessment Schedule (WHODAS II). The BAI was selected over the Fear Questionnaire (FQ) and the Penn State Worry Questionnaire (PSWQ) for its highest associations with anxiety disorders. ROC analysis determined the percentage of functionally impaired with subthreshold anxiety based on found cut-offs.

Results

The CIDI was very modestly associated with functional impairment, possibly because of skip rules, wording or scoring, while the BAI was highly correlated to functional impairment. A score of 11 on the BAI defined clinically relevant subthreshold anxiety. This cut-off identified 36.0% of the most functionally impaired as having subthreshold anxiety.

Limitations

No “natural” cut-off on the BAI for determining subthreshold anxiety could be determined. The cut-off point of 11, based on a large effect size relative to normal anxiety, thus remains somewhat arbitrary.

Conclusions

The questionnaire BAI is more suitable than the interview CIDI to measure clinically relevant, subthreshold anxiety. The BAI score of 11 appeared to be the most appropriate cut-off for identifying clinically relevant subthreshold anxiety.

Introduction

The introduction of classification systems for mental disorders such as the Diagnostic and Statistical Manual (DSM) has greatly improved the reliability of diagnoses. Despite its utility, there has been increasing interest over the last years in symptomatology falling below the diagnostic threshold for a given disorder. The clinical relevance of these subthreshold disorders is evident in several ways. First, subthreshold disorders are shown to be common (Rucci et al., 2003). Second, symptoms even at subthreshold level are associated with reduced quality of life and functional impairment (Rucci et al., 2003, Collings and The MaGPIe Research Group, 2005). Third, individuals with subthreshold disorders seem to be at substantially elevated risk for developing full-syndromal psychiatric disorders (Lewinsohn et al., 2000, Cuijpers et al., 2005). Therefore, especially in community and primary care settings, criteria for defining the presence of relevant subthreshold disorders may aid early detection of and timely intervention for people at risk.

The concept of clinical relevance is of particular importance when dealing with subthreshold disorders. The authors of the DSM-IV added the “clinical significance criterion”, to differentiate mental disorders from normal problems of living. It asserts that symptoms must cause distress or impairment in social, occupational, or other important areas of functioning (Spitzer and Wakefield, 1999). Several authors, especially in the field of depressive disorders, have argued that, overall, the clinical significance criterion does not have added value when it comes to discriminating full-syndromal disorder from normality, as the number and severity of symptoms needed for a full-syndromal diagnosis already imply a high level of distress or impairment (Beals et al., 2004, Zimmerman et al., 2004). However, subthreshold disorders require a less severe and often undefined number of symptoms. Therefore, distress or impairment can be used to separate clinically relevant subthreshold disorder from normality.

So far, most of the research on subthreshold psychopathology has focussed on subthreshold major depressive disorder (MDD). For research purposes, DSM-IV-TR has proposed criteria for minor depression (MD), i.e. similar to those of MDD but with two to four depressive symptoms instead of five or more. This proposed cut-off point received support by a recent study by our research group by linking it to elevated levels of impairment, although our study indicated at the same time that the use of a depression severity scale to define subthreshold depression may be preferable. This was concluded because the severity scale showed a stronger association with functional impairment and is more practical in use below disorder threshold (Karsten et al., 2010).

Unlike for depression, there is no consensus on how to define subthreshold anxiety. This is hardly surprising, as anxiety covers a wider array of diagnoses than depression. The diversity of the anxiety disorders poses an additional challenge for defining subthreshold anxiety. In recent studies, relatively arbitrary criteria for the separate anxiety disorders have been formulated and applied based on DSM-criteria, with restrictions on for instance number of symptoms, frequency of symptoms or level of avoidance (Angst et al., 1997, Heun et al., 2000, Smalbrugge et al., 2005). Other studies used, or recommended, cut-off points on anxiety severity questionnaires, such as a score of at least 9 on the Hamilton Anxiety Rating Scale (HARS; Silverstone and Von Studnitz, 2003). Although a number of studies have shown that subthreshold anxiety is highly prevalent and clinically relevant (Heun et al., 2000, Carter et al., 2001, Zlotnick et al., 2002, Batelaan et al., 2007, Angst et al., 1997, Shankman et al., 2008, Fehm et al., 2008), there are no studies which empirically address how to optimally define and measure clinically relevant subthreshold anxiety by means of functional impairment.

In this study, we aim to evaluate the use of a DSM-based diagnostic interview and select and evaluate one anxiety severity questionnaire for defining clinically relevant, but subthreshold anxiety and to derive an empirical cut-off point by focussing on functional impairment.

Section snippets

Participants and procedure

Data were derived from the long-term Netherlands Study of Depression and Anxiety (NESDA; Penninx et al., 2008). NESDA is a cohort study aimed at describing the long-term course and consequences of depression and anxiety disorders and their predictors. The study started in 2004 and is designed as an eight year longitudinal cohort study among 2981 participants aged 18 through 65 years. Based on the idea that the clinical developmental stage of a disorder is a key determinant of the course of a

Sample statistics

Demographic and clinical characteristics are provided in Table 2. The sample consisted of 947 men (33.5%) and 1881 women (66.5%) with an average age of 41.8 years. The most common somatic conditions were allergies (n = 911), osteoarthritis (n = 604), intestinal problems (n = 528) and high blood pressure (n = 384).

Using CIDI to define subthreshold anxiety

Based on the CIDI, 208 (11.6%) of the 1788 subjects without full-syndromal anxiety reported one or more subthreshold anxiety disorders within the last month: 43 (2.4%) subjects reported

Discussion

Results of this study indicate that the CIDI and the self-report BAI differ greatly in their suitability to assess clinically relevant subthreshold anxiety, i.e. anxiety associated with functional impairment below full-syndromal level. Because of skips in the interview and a, possibly associated, low association with functional impairment on a subthreshold level, the CIDI in its current form was found to be restricted in its usefulness for assessing subthreshold anxiety. The BAI on the other

Role of funding source

The infrastructure for the NESDA study (www.nesda.nl) is funded through the Geestkracht program of the Netherlands Organisation for Health Research and Development (Zon-Mw, grant number 10-000-1002). Zon-Mw had no further role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

Conflict of interests

Dr. Nolen has received speaking fees from Astra Zeneca, Eli Lilly, Pfizer, Servier and Wyeth; unrestricted research funding from Astra Zeneca, Eli Lilly, GlaxoSmithKline and Wyeth; and served on advisory boards for Astra Zeneca, Cyberonics, Eli Lilly, GlaxoSmithKline, Pfizer and Servier. None of the other authors have any disclosures.

Acknowledgements

NESDA is supported by participating universities and mental health care organizations: (VU University Medical Center, GGZ inGeest, Arkin, Leiden University Medical Center, GGZ Rivierduinen, University Medical Center Groningen, Lentis, GGZ Friesland, GGZ Drenthe, Scientific Institute for Quality of Healthcare (IQ Healthcare), Netherlands Institute for Health Services Research (NIVEL) and Netherlands Institute of Mental Health and Addiction (Trimbos Institute).

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