Background: Subsyndromal delirium (SSD) refers to the presence of one or more delirium criteria without a diagnosis of delirium, and it is common in older patients. The prevalence, risk factors, and outcomes of SSD are explored herein.

Design: A systematic review and meta-analysis.

Data sources: PubMed, Web of Science, OVID, PsycINFO, CINAHL, Cochrane Library, CNKI, CBM, Chongqing VIP, and Wanfang databases were searched for studies published from inception to 2021, without language restrictions. Independent reviewers performed quality assessments, data extraction and analysis for all included studies.

Results: A total of 2,426 titles were initially identified, and 22 studies (5,125 individuals) were included in the systematic review. The prevalence of SSD in older adults was 36.4% (95%CI:0.28 to 0.44). Significant risk factors were dementia (OR 5.061, 95%CI:2.320 to 11.043), lower ADL scores (OR 1.706, 95%CI:1.149 to 2.533), lower hemoglobin (SMD -0.21, 95%CI: -0.333 to -0.096), and advanced age (SMD 0.358, 95% CI:0.194 to 0.522), and SSD was associated with poor outcomes, including cognitive and functional decline, increased length of hospital stay, and a higher mortality rate.

Conclusions: SSD has a high prevalence and is associated with many risk factors and poor outcomes. Clinical oversight of patients with SSD should be increased. REGISTRATION: The systematic review was registered on the International Prospective Register of Systematic Review (CRD42021276070). TWEETABLE ABSTRACT: Subsyndromal delirium has a high prevalence and an association with many risk factors and poor outcomes.