<b><i>Background:</i></b> Contrast-induced acute kidney injury (CI-AKI) remains one of the crucial issues related to the development of invasive cardiology. The massive use of contrast media exposes patients to a great risk of contrast-induced nephropathy and chronic kidney disease development, and increases morbidity and mortality rates. The serum creatinine concentration does not allow for a timely and accurate CI-AKI diagnosis; hence numerous other biomarkers of renal injury have been proposed. Renalase, a novel catecholamine-metabolizing amine oxidase, is synthesized mainly in proximal tubular cells and secreted into urine and blood. It is primarily engaged in the degradation of circulating catecholamines. Notwithstanding its key role in blood pressure regulation, renalase remains a potential CI-AKI biomarker, which was shown to be markedly downregulated in the aftermath of renal injury. In this sense, renalase appears to be the first CI-AKI marker revealing an actual loss of renal function and indicating disease severity. <b><i>Summary:</i></b> The purpose of this review is to summarize the contemporary knowledge about the application of novel biomarkers of CI-AKI and to highlight the potential role of renalase as a functional marker of contrast-induced renal injury. <b><i>Key Messages:</i></b> Renalase may constitute a missing biochemical link in the mutual interplay between kidney and cardiac pathology known as the cardiorenal syndrome.