Therefore, the multivariate analysis was carried out on the basis of the two scores classically described as associated with AKI following the injection of a contrast agent (Mehran and GRACE), comparing the improvement in the performance of these scores by the consecutive addition of two variables strongly associated with univariate AKI analysis but that do not figure in the scores and are not collinear: low vascular density defined from the threshold value on the ROC curve (<19.7 mm−1) and NT-proBNP (continuous level rather than a cut-off because the predictive value is higher). The gene discussed is NPPB; the disease is acute kidney injury.