Impact of donor-recipient size mismatch on post-transplant outcomes in kidney transplant recipients: A systematic review.
Asif, S., et al.Transplant Rev (Orlando). 2025 Dec;39(4):100965.
Aims
The aim of this study was to summarise the available evidence on posttransplant outcomes associated with donor-recipient size mismatch in adult kidney transplant recipients.
Interventions
MEDLINE, Embase, and Cochrane databases were searched for literature. Titles and abstracts were screened by a single author, which was followed by full-text screening by two independent authors. Data extraction was performed by two independent reviewers. The Risk of Bias in Non-randomized Studies – of Exposure tool was used to assess the methodological quality of the included studies.
Participants
56 studies were included in the review.
Outcomes
The main outcomes of interest were: Primary outcome: death-censored graft failure Secondary outcomes: kidney function, all-cause graft failure (ACGF), and mortality.
Follow-up
N/A
CET Conclusions
This systematic review reports a well-conducted and rigorous attempt to synthesise a highly heterogeneous body of literature. The review was prospectively registered in the PROSPERO system, conducted in accordance with MECIR standards, and reported using PRISMA guidelines. The search strategy was comprehensive, covering multiple databases over an extended historical period, and study selection, data extraction, and risk-of-bias assessment were performed independently in duplicate. A strength of the study is the explicit use of the ROBINS-E tool for risk-of-bias assessment; the authors transparently report that all included studies were at high or very high risk of bias. Meta-analysis was therefore not advisable, given extreme heterogeneity in definition of size mismatch (there were 15 definitions across the 56 studies), outcome measures and length of follow-up. However, there are several weaknesses that make reliable interpretation difficult. The narrative synthesis categorises study outcomes as “positive,” “mixed,” or “null,” a pragmatic but subjective approach that risks oversimplifying complex, multi-outcome analyses. Most studies were small, single-centre, and retrospective, with inconsistent adjustment for key confounders such as donor quality, recipient comorbidity, and immunological risk. The authors’ conclusion—that existing evidence neither confirms nor refutes the nephron under-dosing hypothesis—is entirely appropriate and well supported. Despite decades of research, and a plausible biological mechanism, there is no consensus on how to define, or make clinical use of, donor-recipient size mismatch in renal transplantation.
Trial registration
PROSPERO - CRD42023455394