The overdiagnosis of depression in non-depressed patients in primary care

Background. The underdiagnosis of depression is an important research topic. Nevertheless, overdiagnosis has not been given the importance it deserves by research into the ability of family physicians to diagnose depression correctly. Objectives. To identify the factors that determine the overdiagnosis of depression by family physicians and to evaluate the clinical significance of this error. Design. Two-phase cross-sectional study. Setting. Primary care centres in Tarragona (Spain). Methods. In the first phase, we screened 906 consecutive patients using Zung's self-rating depression scale (SDS). In the second phase, all the 209 patients with a positive screening and 97 patients with a negative screening (1 out of 7 randomly) were given the Structured Clinical Interview for DSM-IV Disorders, a series of questionnaires, and the family physician judged whether depression was present. In the 186 patients for whom there were no criteria of major depression or dysthymia, the association of various variables with the physicians' overdiagnosis of depression was analysed. Results. The rate of diagnosis of depression in non-depressed patients was 26.5% (95% CI: 19.0-33.9). The factors associated independently with overdiagnosis were the SDS score (OR: 1.05; 95% CI: 1.01-1.10), the Global Assessment of Functioning score (OR: 0.95; 95% CI: 0.90-0.99), previous history of depression (OR: 2.66; 95% CI: 1.12-6.30) and presence of generalized anxiety (OR: 0.42; 95% CI: 0.18-0.97). Conclusion. Family physicians classify as depressed those patients who do not have the formal signs of depression but who do have antecedents of this disorder or a psychological distress that may be prodromal of future depressive episodes.