How should a busy clinician select a depression screening instrument? Ease of administration and interpretation are key. Ideally, a depression screen should function similarly to a vital sign, providing an easy-to-assess yet reliable marker of the need to address a patient’s depression. It is not enough to know that formal depression criteria are met; it is also important to know whether a patient’s functioning is impaired. Research indicates that it is difficult in primary care to “clinically” assess functioning in the face of numerous competing demands,15 even when clinicians know from a screening test that a patient meets criteria for depression.24 For this reason, even watchful waiting for the “positive screening/low impairment” patients25 may be difficult to put into practice.
Two-stage strategy to assess impairment
Use of a 2-stage strategy, combining an assessment of severity with an assessment of depression criteria, appears to answer this dilemma. One study26 has attempted to assess whether this strategy could identify the appropriate patients for clinician attention, using an existing data set that included the PRIME-MD27 and 6 items identified from the original data via factor analyses that assess depression severity.
The results suggest that a combined assessment of depression severity and criteria could help clinicians focus on the most severely depressed patients without missing less severely impaired patients that need treatment (SOR=B).
We suggest the PHQ-9 as the instrument of choice for primary care depression screening because it measures both depression criteria and severity. The PHQ-9 provides a simple way to assess both diagnostic criteria and severity with a single, well-validated instrument. While its PPV is not appreciably greater than 50%, this reflects use in a purely “diagnostic mode,” ie, a cut-point of 10.
A well done, primary care evaluation of the PHQ-9 suggests that a score of 15 or greater reliably indicates both satisfaction of DSM-IV depression criteria and a moderate to severe level of impairment (SOR=A).28 Patients screening positive at this level should be targeted by their physician for a discussion of their symptoms and a recommendation for treatment (SOR=B). Patients with a score of 10–14 meet diagnostic criteria for depression but at a lower level of severity; these patients could be candidates for a strategy of repeat testing or watchful waiting (SOR=B).
Before leaving the topic, a comment is warranted regarding 2-stage screening using an initial 1-or 2-question screen followed by a more lengthy instrument. This type of strategy was embodied in the original PRIME-MD with its 2-question Patient Questionnaire (PQ).27 The intent is to reduce the burden of applying a full diagnostic instrument to an entire practice population. By giving the full instrument only to patients that are positive on the initial 2-question screen, the screening performance burden (as identified in Table 1) is reduced. Use of a brief instrument such as the PHQ-9, which requires only 2 to 5 minutes to fully complete, makes it possible to accurately assess both diagnostic criteria and depression severity in an entire patient population, with little administration burden.
When to screen
Once a decision is made to screen, and an instrument is selected, an interval for screening must be determined. Suggested ranges vary greatly from one-time to annual screening. The recent USPSTF recommendations provide little guidance, stating simply, “the optimal interval for screening is unknown.”11
Regular intervals. One-time screening was found to be cost-effective by Valenstein and colleagues,13 suggesting that, at a minimum, screening should occur when a new patient enters a practice (SOR=A). If a more frequent schedule of screening is desired, depression screening should be linked to other periodic preventive services provided in a practice, such as routine Pap smears or health maintenance exams, to ensure that screening occurs in a systematic fashion (SOR=C).
Risk factors. A practice may also elect to screen based on risk factors (SOR=D). Important risk factors to consider include prior history of treated depression, family history of depression, postpartum status, and any history of substance abuse.
Patients with chronic diseases known to have a high rate of comorbidity with depression—ie, diabetes, congestive heart failure, myocardial infarction—should also be considered as having risk factors for depression.
Ease of implementation
The depression screening instruments reviewed in this paper may all be completed by a patient with a sixth- to ninth-grade reading level, and can therefore be given to patients to complete in an exam room while they wait for their physician. Scoring may be then quickly completed either by the patient or by the physician.
Positive screens should prompt the physician to engage the patient in a discussion of their symptoms, the need for treatment, and a quick assessment for the presence of any suicidal ideation.