Background: Studies investigating the performance of instruments to detect major depressive disorder (MDD) have reported inconsistent results. Subsyndromal depression (SD) has also been associated to increased morbidity, and little is known about its detection in primary care setting. This study aimed to investigate the performance of the Primary Care Evaluation of Mental Disorders (PRIME-MD) to detect MDD and any depression (threshold at SD) in an outpatient unit of a teaching general hospital.
Methods: Nineteen primary care physicians using the PRIME-MD evaluated 577 patients, 240 of them (75% female; mean age, 40.0 +/- 14.4), including all with MDD and a randomly subset of those without MDD, were evaluated by 11 psychiatrists using the Structured Clinical Interview Axis I Disorders, Patient Version (SCIDI/P) for DSM-IV as the standard instrument.
Results: The kappa between the PRIME-MD and the SCID was 0.42 for the diagnosis of any depression and 0.32 for MDD. The distribution of the number of depressive symptoms per patient suggested the existence of a continuum between SD and MDD, and a high frequency of subjects with 4-6 symptoms (close to the cutoff for the diagnosis of MDD).
Limitations: The sample has a modest size and is a subset of an original one.
Conclusion: A continuum between SD and MDD may in part explain the relatively low agreement for the diagnosis of MDD in our sample and possibly in other studies. Studies investigating the performance of screening instruments to detect MDD, should consider the relevance of identifying SD, and the influence of the distribution of the number of depressive symptoms in their results.