Platelet counts associated with acute kidney injury and mortality in critically ill older patients with sepsis: a retrospective single-institution, multi-ICU study

Background: This study aimed to investigate the association of platelet count with sepsis‑associated acute kidney injury (SA‑AKI) and all-cause mortality in older adults. Methods: We enrolled patients aged ≥75 years from 4 medical centers of the Chinese PLA General Hospital between 2015 and 2022. Platelet counts were categorized as ≥200 (reference), 150–199, 100–149, 50–99, and <50 × 10 9 /L. SA-AKI was defined as AKI occurring within 7 days after sepsis diagnosis, categorized as early (≤48 hours) or late SA-AKI (>48 hours to 7 days) based on the duration after sepsis diagnosis. Results: A total of 1936 sepsis cases were enrolled; the proportion with platelet counts below 200 × 10 9 /L was 74.3% (555 with 150–199, 539 with 100–149, 251 with 50–99, and 94 with <50 × 10 9 /L). In total, 74.7% of patients experienced SA-AKI; 53.7% developed early SA-AKI, while 46.3% experienced late SA-AKI. Platelet counts in the 100–149, 50–99, and <50 × 10 9 /L ranges were risk factors for both early and late SA-AKI and were associated with increased 28- and 90-day mortality. For patients in the 150–199 × 10 9 /L range—still within the conventional normal range—mortality risk reached significance only at 365 days (hazard ratio = 1.252). Additionally, SA-AKI itself was an independent risk factor for 1-year mortality. Conclusion: In critically ill older patients with sepsis, lower platelet counts, even within the conventional normal range, are independently associated with increased risks of SA-AKI and short- and long-term mortality. Serial platelet monitoring may serve as a practical early warning tool for identifying high-risk patients.