Prognostic Impact of Laboratory Frailty Index in Elderly Patients with Acute Myocardial Infarction: A Retrospective Cohort Study

Background: Acute myocardial infarction (AMI) is a leading cause of death in the elderly. Frailty syndrome is associated with adverse outcomes. The Laboratory Frailty Index (FI-LAB) provides an objective assessment of frailty, but its prognostic value in older AMI patients remains inadequately investigated. Methods: This retrospective cohort study utilized the MIMIC-IV database and enrolled 3,257 AMI patients aged ≥65 years. The FI-LAB was calculated from 27 laboratory parameters within 24 hours of admission, and patients were stratified into quartiles (Q1-Q4). The primary outcome was in-hospital mortality. Secondary outcomes included 30-day, 90-day, and 360-day all-cause mortality. Multivariable Cox regression, Kaplan-Meier analysis, and ROC curves were used to evaluate the predictive performance of FI-LAB. Results: The median patient age ranged from 76.14 to 77.54 years, with the proportion of females decreasing from 47.66% in Q1 to 64.18% in Q4. In-hospital mortality increased significantly across FI-LAB quartiles (Q1: 8.09% vs. Q4: 28.06%, p<0.001). The 360-day mortality rose from 24.46% in Q1 to 52.74% in Q4. In multivariate Cox analysis, the highest FI-LAB quartile (Q4) was independently related to an elevated risk of in-hospital mortality risk (HR=1.86, 95% CI: 1.35-2.57, p<0.001). The area under the ROC curve (AUC) of FI-LAB alone for predicting in-hospital mortality was 0.646. When combined with conventional severity scores (e.g., OASIS), the predictive performance improved significantly (ΔAUC +0.022). Subgroup analysis demonstrated a more prominent connection among FI-LAB and in-hospital mortality for people lacking of renal illness. (OR=2.98, 95% CI: 2.27-3.90). Conclusion: The FI-LAB serves as an independent predictor of short- and long-term mortality in elderly AMI patients. Its integration with established severity scores enhances risk stratification, offering such an appropriate objective measure for frailty screening in acute care settings.