False positives, false negatives, and the validity of the diagnosis of major depression in primary care.

OBJECTIVE: To explore the issues of diagnostic specificity and psychiatric "caseness" (i.e., whether a patient meets the conditions to qualify as a "case" of a disease or syndrome) for major depression in the primary care setting.
DESIGN: A cross-sectional study comparing the demographic, clinical, and mental health characteristics of patients identified as depressed by their family physicians with those meeting diagnostic criteria for major depression on the criterion standard Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition.
SETTING: The offices of 50 family physicians from private and academic practice in southeast Michigan. PATIENTS: A total of 1580 consecutive adult patients being seen for routine primary care services, from whom a weighted sample of 372 patients completed a set of mental health screening and diagnostic instruments. MAIN OUTCOME MEASURES: Patients were assigned to 1 of 4 groups (true positive, false positive, false negative, and true negative) based on clinician identification and Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition diagnosis. Differences between the 4 groups in demographic and clinical characteristics, scores on mental health instruments and mental health history were explored.
RESULTS: Physician identification of depression was strongly associated with increased familiarity with the patient and the presence of suggestive clinical cues, such as history of or treatment for depression, patient distress, and presence of vegetative symptoms. Patients in the false-positive group displayed significantly higher levels of distress and impairment and were significantly more likely to have a history of mental health problems and treatment than were those in the true-negative group. The 2 "misidentified" groups, false positives and false negatives, were indistinguishable in their clinical characteristics (impairment, distress, or mental health history). Both groups' scores occupied the middle ground between true positives and true negatives on most clinical characteristics. Physicians appeared to discriminate between these 2 groups on the basis of their knowledge of the patient's clinical history.
CONCLUSIONS: Misidentification of depression in primary care may be in part an artifact of the use of the psychiatric model of caseness in the primary care setting. Our results are most consistent with a chronic disease-based model of depressive disorder, in which patients classified as false positive and false negative occupy a clinical middle ground between clearly depressed and clearly nondepressed patients. Family physicians appear to respond to meaningful clinical cues in assigning the diagnosis of depression to these distressed and impaired patients.