How useful is a screening instrument?

Dozens of studies have been published about the psychometric qualities of instruments used for screening cancer patients for psychological distress. The aim of these psychometric evaluations is to choose an instrument that can identify patients who are in need of professional psycho-oncological help. The viewpoint that only selected patients should be offered professional help is the motivation for developing such an instrument: ‘Routine screening using self-report measures helps ensure therapeutic interventions are offered to those in need’ [1]. ‘The aim of brief screening is to identify undiagnosed patients who require treatment and to guide them to the appropriate treatment’ [2]. Although such ideas seem self-evident, the aim of this letter is to express our doubts about the certainty with which these statements are accepted. A quick scan in Web of Sciences yielded approximately 30 psychometric studies that compared the characteristics of several screening lists for cancer patients, or the outcome of a screening list with Diagnostic and Statistic Manual-IV diagnoses determined by means of a psychiatric interview. Seven of these studies were published in Psycho-Oncology [3–9]. This is in contrast with the paucity of studies dealing with the practical use of screening instruments [10]. One exception is the study by Sollner et al. [11]. During a period of 6 months 100 patients were screened in a RadioOncology Unit in Innsbruck. Approximately one third suffered from moderate to severe anxiety or depression, but only 58% of them accepted counselling. On the other hand, of those patients who fell below the cut-off criterion 45% were interested in and actually received counselling. Counselling was offered to all patients with moderate or severe distress and to those expressing a wish for such support. The findings of this study can be formulated in a different way: Of the patients who actually received supportive counselling, 38% would have been referred to counselling on the basis of moderate to high distress scores only, whereas 71% would have been referred if based solely on the question ‘Are you interested in receiving supportive counselling’? The other two exceptions have been published as conference abstracts only. In the study by Tiller [12], 343 new patients were screened during a period of 16 months in an oncology centre in Sydney. Approximately one quarter of the patients fulfilled the cutoff criterion on the Hospital Anxiety and Depression Scale (HADS), but only a minority (30%) of the patients identified actually turned to a clinical psychologist for help. During the same period, 103 patients were referred for reasons other than a sufficiently high score on the HADS, such as adjustment problems, flat affect, relationship problems and hereditary cancer issues. A discrepancy between screening results and referrals was also reported by Jones and Doebbeling [13] in a study on screening for depression among Veterans with cancer. Of the 1967 participants in this study, 65% were screened. Of those screened 17% scored positive and of the patients who scored positive only 11% were referred to mental health clinics. These findings indicate that the effectivity of a screening instrument does not comply with theoretical ideas. It is possible that a screening instrument could be useful in exceptional conditions, especially in a research project. However, it is reasonable to assume that the use of a screening instrument in busy hospitals is more likely to reflect the examples in the three studies cited above. In a critical review, Palmer and Coyne describe the somewhat disappointing results of studies that evaluated the usefulness of screening instruments for depression in primary medical care [14]. They write, ‘Sentiment in favour of screening in medical settings is so strong that expressions of scepticism must assume a high burden of proof. Yet, seldom are data presented demonstrating that screening for depression improves functional status and mental or physical health, or that screening is cost effective’ [14]. Indeed, most studies did not prove any health benefits after introducing a screening instrument in primary care practices. Coyne also doubts the ‘inherent assumption of many screening efforts that these otherwise undetected patients differ from detected patients only in our knowledge of their depression’ [15]. However, they found evidence in the studies they cite that patients whose identification depends on screening have milder forms of depression and/or have a negative attitude about antidepressant medication. This would make it more difficult to demonstrate the treatment effects of screening efforts. They also suggest that ‘the effectiveness of screening lies not in the number of depressed patients identified, but in the number of depressed patients who, as a result of screening positive, accept and benefit from treatment that they would not otherwise have been offered’. In a screening programme for major depressive disor-