Background: Depression is a common reason for consultation with a primary care physician, but the diagnosis can be challenging. Up to 80 percent of patients with depression report physical symptoms, and many patients are reluctant to accept a psychiatric diagnosis. Even highly motivated physicians only recognize an estimated 36 to 56 percent of depressed patients in primary care. Many screening tools have been developed to assist in the diagnosis of depression. Studies indicate that these tools have an overall sensitivity (ability to detect a true case) of 84 percent and specificity (ability to rule out a negative case) of 72 percent.
Because screening tools require time to complete, several short tools have been proposed; the simplest tools include only one question. Current British guidelines recommend a two-question screening tool, but the validity of this and other short screening tools has not been established. The National Institute for Health and Clinical Excellence (NICE) published a guideline that recommends the use of two questions from the Patient Health Questionnaire-2: “During the past month, have you often been bothered by feeling down, depressed, or hopeless?” and “During the past month, have you often been bothered by having little interest or pleasure in doing things?” The content of other short screening tools was not defined by NICE. Mitchell and Coyne studied the accuracy of ultra-short screening tools in the diagnosis of depression in primary care patients.
The Study: The authors conducted a pooled analysis and meta-analysis of relevant studies. Ultra-short screening tools were defined as including up to four questions and requiring less than two minutes to complete; short screening tools were defined as including five to 14 questions and requiring two to five minutes to complete. Studies were identified by a search of several electronic databases and full-text collections. Study quality was determined by examining aspects such as the type of patients studied, data integrity, reference criteria used, drop-out rate, and type or severity of depression studied. Data were abstracted from each eligible study using standardized protocols.
Results: Of the 75 studies identified, 22 met standard criteria for quality and were conducted in primary care settings. The eight studies of one-question tools involved 17,624 patients, 1,881 of whom were diagnosed with depression after more detailed testing. One-question tools correctly identified only 601 patients with depression (sensitivity of 31.9 percent) and incorrectly identified 479 nondepressed patients as having depression (specificity of 96 percent). The 14 studies of two- or three-question tools involved 9,653 patients, 17.6 percent of whom were diagnosed with depression after more detailed testing. The two- or three-question screening tools correctly identified 1,253 patients with depression (sensitivity of 73.7 percent); the specificity was 74.7 percent. Removing one study that required a positive answer to both questions improved the sensitivity to 79.4 percent.
The meta-analysis showed that ultra-short screening tools were significantly better than chance in diagnosing depression in primary care. Nevertheless, one-question tools identified only three out of 10 depressed patients. Two- or three-question tools were significantly more effective, identifying eight out of 10 depressed patients. Both types of ultra-short screening tools had very high false-positive rates with only four out of 10 identified patients actually meeting criteria for depression.
Conclusion: The authors conclude that ultra-short screening tools may be useful to rule out depression, but the tools should be used only when more detailed resources are available for follow-up screening for those who test positive for depression. The authors point out that the diagnostic acumen of primary care physicians may be much higher than commonly reported. Studies of primary care physicians in New Zealand indicate detection rates of 56 to 85 percent.