Validation of the pediatric index of mortality 3 in a pediatric intensive care unit in Thailand: a prospective, single-center observational study

The Pediatric Index of Mortality 3 (PIM3) is a widely used severity-of-illness score. This study aimed to validate PIM3 performance in patients aged < 18 years admitted to a Thai pediatric intensive care unit (PICU). This prospective, single-center, observational study included patients aged < 18 years admitted to the PICU between April 1, 2024, and March 31, 2025. PIM3 performance was assessed using the area under the receiver operating characteristic curve for discrimination. Calibration was primarily evaluated utilizing the Hosmer-Lemeshow goodness-of-fit test, and the standardized mortality ratio (SMR). A total of 617 patients were enrolled, with an observed mortality of 2.43% (15 deaths), lower than the PIM3-predicted mortality of 3.63%. The area under the receiver operating characteristic curve was 0.917 (95% CI 0.842-0.993). The Hosmer-Lemeshow goodness-of-fit test showed no statistically significant difference between observed and predicted mortality (χ² = 7.561; P = 0.478). The standardized mortality ratio was 0.67 (95% CI 0.37-1.11). In this single-center cohort with a low mortality event count, PIM3 demonstrated good discrimination and acceptable calibration, although the SMR suggested a non-statistically significant trend toward overpredicting mortality.