Combining the GP’s assessment and the PHQ-9 questionnaire leads to more reliable and clinically relevant diagnoses in primary care

Background Screening questionnaires are not sufficient to improve diagnostic quality of depression in primary care. The additional consideration of the general practitioner’s (GP’s) assessment could improve the accuracy of depression diagnosis. The aim of this study was to examine whether the GP rating supports a reliable depression diagnosis indicated by the PHQ-9 over a period of three months. Methods We performed a secondary data analysis from a previous study. PHQ-9 scores of primary care patients were collected at the time of recruitment (t1) and during a follow-up 3 months later (t2). At t1 GPs independently made a subjective assessment whether they considered the patient depressive (yes/no). Two corresponding groups with concordant and discordant PHQ-9 and GP ratings at t1 were defined. Reliability of the PHQ-9 results at t1 and t2 was assessed within these groups and within the entire sample by Cohen’s Kappa, Pearson’s correlation coefficient and Bland-Altman plots. Results 364 consecutive patients from 12 practices in the region of Upper Bavaria/Germany participated in this longitudinal study. 279 patients (76.6%) sent back the questionnaire at t2. Concordance of GP rating and PHQ-9 at t1 led to higher replicability of PHQ-9 results between t1 and t2. The reliability of PHQ-9 was higher in the concordant subgroup (κ = 0.507) compared to the discordant subgroup (κ = 0.211) (p = 0.064). The Bland-Altman Plot showed that the deviation of PHQ-9 scores at t1 and t2 decreased by about 15% in the concordant subgroup. Pearson’s correlation coefficient between PHQ-9 scores at t1 and t2 increased significantly if the GP rating was concordant with the PHQ-9 at t1 (r = 0.671) compared to the discordant subgroup (r = 0.462) (p = 0.044). Conclusions The combination of PHQ-9 and GP rating might improve diagnostic decision making regarding depression in general practices. PHQ-9 positive results might be more reliable and accurate, when a concordant GP rating is considered.