<![CDATA[Introduction: Late-life major depressive disorder (MDD) is a leading contributor to disability and excess mortality, yet most affected older adults are seen exclusively in primary care. Reported prevalence estimates vary more than sixfold across studies. This review aimed to quantify the pooled prevalence of MDD and clinically significant depressive symptoms among older primary-care attendees. Methods: The study strictly adhered to the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) 2020 guidelines of observational primary studies reporting depression prevalence in adults ≥55 years in primary care using criterion-standard diagnostic instruments (SCID, MINI, CIDI, PRIME-MD, ICD-10/DSM checklist) or validated screening scales (GDS, PHQ-9). Risk of bias assessed with JBI checklist, certainty with GRADE. Results: Eighteen studies (N=15,200) from 11 countries were included; 16 studies (N=14,000) contributed to pooling. Pooled prevalence across all case definitions: 24.63% (95% CI 17.80-33.03; I²=98.6%). Diagnostic-interview MDD prevalence: 14.23% (95% CI 9.33-21.10; k=5; I²=95.7%). Screening-scale positivity: 30.59% (95% CI 21.16-41.99; k=11; I²=98.4%) — an absolute difference of 16.4 percentage points. Prevalence was higher in LMIC (30.97%) vs HIC (17.83%; p=0.048). Regional: Middle East-North Africa 44.99%, sub-Saharan Africa 33.94%, East-Southeast Asia 16.82%, Europe 11.43% (p<0.001). GDS: 32.24%, PHQ-9: 23.69%. Consistent risk factors: female sex, widowhood, chronic disease, low income, low education, advanced age, functional limitation, loneliness. Physician recognition was very low (0-63%; κ=0.156); only 22.9% of MDD patients received antidepressants. Discussion: Approximately 1 in 4 older primary-care attendees screen positive for depression, and 1 in 7 meet MDD criteria — several-fold higher than community estimates. Heterogeneity is not statistical noise but is structured by case definition, instrument, income setting, and region. Screening without diagnostic confirmation yields >50% false positives in older adults. The recognition and treatment gaps are the most actionable findings. Conclusion: Major depression is highly prevalent, under-recognised, and undertreated among older primary-care attendees globally, with the greatest burden in LMIC. Two-stage screening (brief scale followed by diagnostic interview) integrated into geriatric primary care, coupled with collaborative-care pathways, is strongly warranted.]]>
