To evaluate the validity and correlates of inaccurate clinically diagnosed moderate/severe ICD-10 major depressive disorder (MDD) and psychiatric comorbidities in adult inpatients.

The multicenter Patient Characteristics, Validity of Clinical Diagnoses and Outcomes Associated with Suicidality in Inpatients with Symptoms of Depression (OASIS-D) study enrolled 18- to 75-year-old inpatients with MDD who underwent assessments for clinical, illness, and treatment characteristics, including the Mini-International-Neuropsychiatric-Interview (MINI). False-positive clinically MDD diagnoses were characterized via MINI. Diagnostic agreement between clinical and MINI-based psychiatric comorbidities was assessed with kappa-statistic.

Among 401 patients (median age = 33.0 years; female = 57.1%), 42 (10.5%) were false positive for MDD (i.e., different primary diagnosis). Reasons for misdiagnosing MDD exclusive to false-positive cases included bipolar disorder (45.2%), subsyndromal depression (16.7%), and physical illness-related/substance use disorder (SUD)-related depression (4.8%), whereas missed diagnoses that could also occur in true-positive, MINI-based MDD patients included primary SUDs (23.8%) and primary anxiety disorders (9.5%). Among comorbidities, greatest disagreement between clinical and MINI-based research diagnoses existed for antisocial personality disorder (0% vs. 5.2%, κ =0), followed by anxiety disorders (7.5% vs. 45.1%, κ =0.17), obsessive-compulsive disorder (3.0% vs. 8.7%, κ =0.27), SUDs (11.0% vs. 28.4%, κ =0.29), eating disorders (3.5% vs. 7.2%, κ =0.39), and posttraumatic stress disorder (10.7% vs. 23.7%, κ =0.40).

Bipolar depression and SUDs contributed to two thirds of misdiagnosed MDD. Missed comorbidities included mostly anxiety disorders, SUDs, and PTSD. Accurate diagnostic assessment, including longitudinal history, is essential to reduce misdiagnosis and ensure guideline-based treatment for psychiatric disorders in MDD inpatients.