Preoperative plasma leptin levels predict delirium in elderly patients after hip fracture surgery

• Hypoleptinemia is found in elderly patients with delirium after hip fracture surgery.
• Leptin is an independent predictor for delirium in elderly patients after hip fracture surgery.
• Leptin has predictive value for delirium in elderly patients after hip fracture surgery.

Leptin is considered to be a modulator of the immune response. Hypoleptinemia increases the risk for Alzheimer's disease and vascular dementia. The present study aimed to investigate the ability of plasma leptin level to predict delirium in elderly patients after hip fracture surgery. Postoperative delirium (pod) was evaluated using the Confusion Assessment Method. Prolonged postoperative delirium (ppod) was defined as delirium lasting more than 4 weeks. Plasma leptin levels of 186 elderly patients and 186 elderly controls were measured by an enzyme-linked immunosorbent assay. Plasma leptin level was substantially lower in patients than in controls (4.6 ± 2.2 ng/ml vs. 7.5 ± 1.8 ng/ml, P < 0.001). It was identified as an independent predictor for pod [odds ratio, 0.385; 95% confidence interval (CI), 0.286–0.517; P < 0.001] and ppod (odds ratio, 0.283; 95% CI, 0.152–0.527; P < 0.001) using a multivariate analysis, and had high area under receiver operating characteristic curve for pod [area under curve (AUC), 0.850; 95% CI, 0.790–0.898] and ppod (AUC, 0.890; 95% CI, 0.836–0.931). The predictive value of leptin was markedly bigger than that of age for pod (AUC, 0.705; 95% CI, 0.634–0.770; P = 0.002) and ppod (AUC, 0.713; 95% CI, 0.642–0.777; P = 0.019). In a combined logistic-regression model, leptin improved the AUC of age to 0.890 (95% CI, 0.836–0.931) (P < 0.001) for pod and 0.910 (95% CI, 0.860–0.947) (P = 0.005) for ppod. Thus, preoperative plasma leptin level may be a useful, complementary tool to predict delirium and also prolonged delirium in elderly patients after hip fracture surgery.