Development of a quantitative donor risk index to predict short-term mortality in orthotopic heart transplantation

Abstract

No standard index based on donor factors exists for predicting mortality after orthotopic heart transplantation (OHT). We utilized United Network for Organ Sharing (UNOS) data to develop a quantitative donor risk score for OHT. We examined a prospectively collected open cohort of 22,252 patients who underwent primary OHT (1996 to 2007). Of the 284 donor-specific variables, those associated with 1-year (year) mortality (exploratory p-value < 0.2) were incorporated into a multivariate (MV) logistic regression model. The final model contained donor factors that improved the explanatory power (by pseudo-R2, area under the curve and likelihood ratio test). A quantitative donor risk score was created using odds ratios (ORs) from the final model. For external validity, a cross-validation strategy was employed whereby the score was generated using a randomly generated subset of cases (n = 17,788) and then independently validated on the remaining patients (n = 4,464). A 15-point scoring system incorporated 4 variables: ischemic time; donor age; race mismatching; and blood urea nitrogen (BUN)/creatinine ratio. Derivation and validation cohort scores ranged from 1 to 15 and 1 to 12, respectively (mean 4.0 ± 2.1 for each). Each increase of 1 point increased the risk of 1-year death by 9% (OR = 0.09 [1.07 to 0.12]) in the derivation cohort and 13% (OR = 0.13 [1.08 to 0.18]) in the validation cohort (each p < 0.001). The odds of 1-year mortality by increments of 3 points were: 0 to 2 points (reference); 3 to 5 points (OR = 0.25 [1.12 to 0.40], p < 0.001); 6 to 8 pts (OR = 0.77 [1.56 to 2.02], p < 0.001); and 9 to 15 points (OR = 1.92 [1.54 to 2.39], p < 0.001). Donor risk score was predictive for 30-day mortality (OR = 0.11 [1.08 to 0.14], p < 0.001) and 5-year cumulative mortality (OR = 0.11 [1.09 to 0.13], p < 0.001). We present a novel donor risk index for OHT predicting short- and long-term mortality. This donor risk score may prove valuable for donor heart allocation and prognosis after OHT.